Sullivan's Blog

How to Remove Too Much Colored Release Agent

2009-03-30T09:25:00.000-07:00

Question:
I installed a stamped concrete slab for some homeowners, and they decided they wanted more of the colored release agent removed from the slab after I had already sealed it. They thought it looked too dark. How do I remove the sealer and wash off the release to reduce the intensity of the secondary color?

Answer:
When concrete is stamped using colored antiquing release, the stamps actually push some of the colored powder into surface of the concrete. This process causes the secondary color to be permanently encapsulated in the surface paste of the concrete. So, without writing a Master’s thesis and getting into a lot of chemistry, I will keep it simple and tell you that it will be very hard to remove the colored release powder if the slab was stamped properly. The sealer, however, can be removed with a chemical stripper (see Advice on Using Chemical Strippers and The Concrete Network article Best Method for Stripping Sealers).

During that process, you may be able to remove some of the release color. Try attacking the concrete with a stiff-bristle brush, and scrub until you remove some color. This can take a long time, and produce a lot of sweat. If you need to remove more color, try using a very dilute acid (40 parts water to 1 part muriatic acid). Spray down the dilute acid, covering small sections of the slab at a time, then scrub it in with a brush and rinse with soapy water. The acid will actually take up some of the concrete paste, along with some of the color. Test this in an inconspicuous area first to be sure you are getting the results you and the homeowners desire.

How to Avoid the Orange Peel Look

2009-03-30T09:17:00.000-07:00

Question:
I applied a two-component high-solids epoxy sealer to a concrete floor, putting down the first coat in December and the second coat two months later. Prior to applying the second coat, I sanded the floor and wiped it with xylene. I used a squeegee to apply the sealer, then rolled it with an epoxy roller with a 1/8-inch nap thickness. Then I rolled over it with a spike roller. The sealer did not lay out smoothly, and is very uneven and rough. What went wrong, and how do I fix it?

Answer:
This is a classic case of “fish eyeing” or “orange peel,” two different terms that describe the same issue. It’s caused when the second coat of sealer fails to “wet out” or become one with the first sealer coat. This can be due to chemical or dirt contamination or because the surface is just too hard and smooth to accept the new coat of sealer. By wiping the floor with xylene, you may have left behind a chemical residue. Or maybe you didn’t sand the surface enough prior to applying the second coat of sealer. How did you sand, and with what grit of sandpaper or screening? When sanding, you have to micro-scratch the surface enough to reduce the surface tension that can prohibit the second coat from adhering to the first coat. The two sealer coats look like they are repelling each other, which can occur with high-solids coatings if the first coat is not prepared properly.

This bumpy orange-peel appearance is caused when a second coat of sealer fails to bond with the first coat due to surface contamination.

Unfortunately, the fix can be a bit involved. If the sealer has completely cured and is hard, you can sand the surface to remove the uneven layer, and then reseal. Or if light sanding removes the rough layer, you can try applying multiple coats of wax to help smooth the surface. You can also use a chemical stripper to remove most or all of the sealer, but this is definitely more involved and may not take off all the sealer.

Do Admixtures Inhibit Stain Color?

2009-01-09T08:32:00.000-08:00

Question:
We seem to be experiencing more and more concrete slabs that are not taking acid stains, even when we grind them first with a #150-grit diamond disc. The acid stain is not even producing full color development inside a ¼-inch sawcut. The problem is only happening on slabs less than two years old. We were told by stain and sealer manufacturers that the problem is due to the addition of plasticizers to the concrete or that the portland cement in the concrete was replaced with as much as 20% fly ash. Do you have any test data to substantiate this, and could the use of sodium silicates and lithium hardeners also have negative effects on the development of stain color?

Answer:
I have no hard evidence to support that stains don’t take due to the addition of plasticizers to the concrete, but evidence does exist to support that a high fly ash content will limit stains from developing their full color. If you consider that admixtures such as plasticizers and water reducers have been used for decades in concrete, I doubt a strong case can be made that these are causing the problems. Plasticizers are used in such small amounts in comparison to the overall volume of concrete that it would take a mix design with massive amounts of these chemicals to cause an issue. Chemical admixtures used in excess may cause a reduction in color development, but the chemistry and historical track record do not support outright color rejection.

In terms of fly ash, this can cause a problem, but only if it is used in high doses—in excess of 20%. Fly ash will increase durability and concrete density and consume free lime, thus “stealing” the raw materials that stains need to produce color. (Acid stains need to be able to penetrate into the concrete to get at the free lime for a reaction to occur.) I always recommend pure cement mix designs or the use of less than 10% fly ash if staining is to be performed.

The other factor to consider is that in the last two years, the green movement has come into its own, promoting the use of all kinds of eco-friendly methods and materials. Using fly ash is considered to be an eco-friendly manufacturing method and increases the LEED (Leadership in Energy and Environmental Design) value of concrete. It also reduces material costs at the ready-mix facility. Those forces have made it politically correct to use more fly ash, without much consideration for the effects down steam.

Keep in mind that it is your responsibility, as the stain applicator, to make sure the slab is ready to accept the stain, whether you poured the concrete or not. Take the time to look at the batch tickets to see what’s in the concrete mix, and always do a sample prior to stain installation to ensure that the color is correct.

We also need to look at why and how stains work to understand why problems might be occurring. I will throw out a few ideas and opinions based on what I have observed in regard to acid stains over the last few years.

-Advancements in placement and finishing techniques create a tighter, denser concrete, which makes it harder for acid stains to take. Increased surface preparation is needed.
-"Closing" the surface vs. "opening" the surface by grinding. I am seeing more and more applicators using diamonds to try and open up the concrete, but in actuality they are tightening the surface even more.
-Total lack of surface preparation—just apply the stain and hope for the best. There are not many situations in which concrete does not need some type of surface preparation prior to staining.

To answer the second part of your question regarding the use of chemical hardeners and densifiers, they will cause color reduction if applied prior to the stain. No matter whether the hardener is a sodium-, lithium- or potassium-based product, these materials create a harder and denser surface through chemical means. Anything that will retard stains from getting into the concrete will have an effect on stain color. That said, the type of concrete and surface profile will play a big part as well. The tighter the surface, the more effect a chemical hardener will have in terms of retarding stain color. The only way to determine the effect these chemicals will have on color development is to prepare a prejob sample.

As a side note, the use of concrete dyes eliminates most of the issues discussed above. Dyes are significantly smaller in particle size than acid stains, penetrate into much harder and denser concrete than stains, and don’t need any free lime to develop their color. The trend in the industry is moving toward dyes and away from stains based on ease of use, time and labor savings, and elimination of potential color problems.

Epoxy in Sawcuts Leaves White Haze

2009-01-09T08:17:00.000-08:00

Question:
I stained an old concrete floor the other day and sealed it with a two-part 100%-solids epoxy. I love the way the epoxy looks, but there are minor imperfections, such as trapped lint and small bubbles, that keep the surface from looking like a perfect sheet of glass. Also, there are really deep sawcut lines in the floor (1 to 2 inches), and the epoxy that went into the sawcuts stayed a milky white color.

What is the best method to apply the epoxy to avoid these issues?

Answer:
Welcome to the world of high-performance coatings, and the viscosity that is associated with them. Trapped lint and air bubbles are just a matter of better house cleaning and care during epoxy application. Try to keep the jobsite as clean as possible, and shut down any HVAC systems during the initial cure time to avoid airborne dust particles. When applying the epoxy, wear medical shoe covers, such as those used in hospitals, rather than cotton socks, which give off lots of lint. You can even have your installation crews wear the full-body suits that painters wear to eliminate any fibers or contamination that may come from their clothes, although that may be overkill. Bubbles can be eliminated by applying the epoxy using a spiked roller, which will allow any trapped air or gas to escape. Midwest Rake is a good source for this type of roller. (See this page from their catalog.)

As for the white haze that developed in the sawcuts, the cause is either trapped moisture or the coating was applied too thickly. The fact that the sealer is a 100%-solids product and does not need evaporation to cure leads me to believe that moisture is the culprit. Cracks and joints are common places for water to hide. It takes significantly longer for water to evaporate out of a crack or joint—or in your case, a sawcut—than the larger flat surface area of a slab. With such deep sawcuts, you need to give the floor plenty of extra dry time or use a leaf blower or high-pressure air hose to speed drying. Unfortunately, the chance of the white haze going away on its own with a 100%-solids product 1 to 2 inches thick is slim. You may need to grind out or chemically strip the coating from the sawcuts. When you go to reseal the cuts, make sure they are dry and fill them with multiple thin applications of epoxy vs. one thick application. Thin coats of materials will give any trapped air or gas a better chance to migrate to the surface and escape.

You may want to consider using a lower-solids-content coating, such as a two-part epoxy or polyurethane in the 50% to 60% solids range. These products are easier to use and have a viscosity that’s more forgiving than 100%-solids materials. Plus, they will provide almost the same performance when applied in multiple coats.

Cause of Shadowing Through an Overlay

2008-11-14T11:29:00.000-08:00

Question:
We did a "rough trowel" overlay on a driveway in Pennsylvania, and three weeks after the job was complete dark marks appeared. At first, they would come and go, but now they are permanent. When the homeowner washes his car, the water that gets on the driveway surface also starts to darken the overlay. We think that moisture from underneath the overlay and penetrating from the top in areas where the overlay and sealer have chipped off is causing the darkening. We are now looking for a fix to this problem.

Answer:
This is what is known as “shadowing.” Either contamination or moisture is causing a shadow or darkening to show through the overlay. The area where it is darker could be the shadowing of a crack, oil stain or repair material. Based on the photo, the cause appears to be moisture, especially in the areas around the control joint.

To fix the problem, you need to find where the moisture is getting under the overlay and stop its entry to prevent the shadowing from getting worse over time. The joints are easy – just caulk them with a flexible polyurethane caulk. Also, make sure to caulk all edges and places where water can migrate between the overlay and concrete substrate. The main areas are a bit trickier. You will need to be grind down the overlay, treat the concrete with a penetrating waterproofing sealer, and then reapply the overlay.

How to Test Sealers for Adhesion

2008-11-07T11:20:00.000-08:00

Question:
How do I know if the sealer on my stamped concrete patio is still working, or if it’s beginning to lose adhesion and needs to be stripped and replaced?

Answer:
There are two common ASTM field tests for determining sealer adhesion in the field, known as “tape tests.” The specific application and performance criteria for these tests are described in ASTM D3359, “Standard Test Method for Testing Adhesion by Tape Test,” available at ASTM International.

The first of the two tests is the X-cut test and is primarily intended for use with coatings on metal substrates. The test better suited for the thin-build sealers and coatings often used on decorative concrete is the cross-hatch test. It provides the best results on coatings less than 5 mils (125 microns) thick. The test consists of a cross hatch, or “#” pattern, cut into the sealer or coating with a sharp razor blade or scalpel. A cutting guide or special cross-hatch cutter should be used if testing per ASTM specifications. For a simple field test to determine adhesion, hand cutting will suffice. After making the cross-hatch incision, apply pressure-sensitive tape or clear plastic packing tape over it and then rub over the tape until it is well adhered to the sealer or coating. Next, remove the tape and assess the results per ATSM D3359 guidelines. If the sealer is well adhered, the cross-hatch pattern should be clean with very little or no sealer removed by the tape. If the sealer is exhibiting adhesion failure, the cross-hatch cuts will have rough edges and sealer may be present on the tape. If the coating can be easily removed at the cut marks, this is another indication that the sealer is compromised and may no longer be well adhered to the substrate.

Cross-hatch test for sealer adhesion being performed on stamped concrete.

Beware of Applying Acrylic Sealer Too Thickly

2008-09-11T16:18:00.000-07:00

Question:
Here’s a photo of a self-leveling overlay that I stained and sealed with a 30%-solids acrylic sealer. The slab is in a screened porch under a deck. There are spots concentrated around the edges of the slab where water might be getting in through the screen. I thought the spots were left from the water, but I tried scrubbing them and they won't come off. They do disappear when they are wet.

Have you ever seen anything like this? Normally when my sealer has moisture issues, it appears cloudy. Some of these spots almost appear as if the sealer has cracks in it. It’s weird!

Answer:
The acrylic sealer is actually fracturing. Typically this occurs when the sealer is applied too heavily, as it appears to be in this case. Acrylic sealers are designed to go down very thin. Even with two coats, the thickness should be only about 1 to 2 mils. To give you some reference, a credit card is about 120 mils thick.

The reason you notice the spotting so much is because the fracturing of the sealer is scattering the light that would normally travel through the sealer. When light can travel through a sealer without interference, you’ll see a nice, clean reflection. Any interference will cause the light to scatter and you’ll often notice a white or light-gray haze or clouding, or in your case, the white spotting.

I am not a fan of acrylic sealers with a solids content above 24%. At higher solids, you need to be very careful to apply the sealer thinly. Acrylics are tough stuff, but they are prone to cracking once they exceed 1 to 2 mils in thickness. The substrate they are applied to also plays a part. Self-leveling overlays are pretty dense and usually have a polymer-rich paste on the surface. Unless this paste is sanded off prior to staining or sealing, you run the risk of limited sealer penetration and compromised adhesion. Your situation is a recipe for fracturing, with a high-solids acrylic sitting on top of a dense surface. Opening the surface by lightly sanding is usually enough to allow penetration.

If you like the high-gloss look of an acrylic but want to avoid this problem in the future, consider using a two-part polyurethane, which is designed to go down at 3 to 5 mils. Or spread out the acrylic more thinly to achieve a 1- to 2-mil thickness and then apply multiple coats of a wax-modified finish coat or sacrificial topcoat designed for concrete floors.

Acrylic sealers applied too heavily may fracture.

Repairing Shrinkage Cracks in Stamped Concrete

2008-09-04T16:11:00.000-07:00

Question:
How do I deal with small cracks and fractures that occur along the edges and corners of the stone imprints in some of my stamped concrete work? They are random and do not occur on all my projects. They seem to happen with deeper, more aggressive stone patterns. How do I fix these cracks, and how do I keep them from happening in the future?

Answer:
These are shrinkage cracks caused by pushing imprinting tools into the concrete after the surface has become too hard. This surface hardening, known as “crusting,” can be caused by exposure to sun and wind, overfinishing, the concrete mix design, and even the concrete color (darker colors more readily absorb heat from the sun).

A good analogy is what happens when you cook pudding. When the pudding comes off the stove, it’s a viscous liquid, similar to concrete when it comes out of the truck. The pudding then goes into the fridge to cool. If it cools too quickly, the rapid temperature drop causes a skin to form on the surface. The pudding then thickens and hardens from the top down. The same thing occurs when concrete dries too fast from the top down. Remedies for reducing surface crusting include using admixtures to slow the concrete set time, using surface evaporation retarders, avoiding darker colors, and scheduling the concrete pour for the coolest time of the day. Using stamping tools with deep grout lines, such as random stone and large slate patterns, can aggravate the cracking problem.

One way to repair these small cracks is to use a colored cement paste, or color patch. Some color hardener manufacturers offer these patches in their standard color palette for use in filling and repairing these types of cracks and small popouts. Some contractors will sift the sand out of the color hardener they are using on the project and use this to make a color patching material. I recommend wetting color patch materials with a 50:50 blend of concrete bonding polymer and water. Use a wooden tongue depressor or gloved finger to smear the color patch into the cracks. Soften the edges with a damp rag or sponge to blend the patch and color into the slab. Let these repairs cure for 24 hours.

Advice on Using Chemical Strippers

2008-07-31T10:59:00.000-07:00

Question:
What is the best way to chemically strip sealers from concrete.

Answer:
The issue of stripping sealers is never at the forefront of what I write about, but in some cases it is required in order to repair or complete a specific decorative project.

The first thing that needs to be clarified is what a chemical stripper is and how these strippers work. Too often I get asked which solvent I recommend for stripping a sealer. First and foremost, solvents are not strippers! A solvent may loosen a sealer or coating, but left alone after spraying, the solvent will have little to no long-term effect on the sealers commonly used in the decorative industry. Using a solvent to eliminate trapped moisture or rewet the surface is a whole different process, and is covered in other blog entries (read Blisters, Bubbles on Sealer Surface and Preventing Moisture Problems). A chemical stripper is a chemical compound that actually destroys the coating, usually turning it into sludge. Another common misconception is that an acid will remove a sealer. Most common acids (such as hydrochloric and phosphoric) will have no effect on cured acrylics, polyurethanes or epoxies.

Strippers come in many forms, but they all have one thing in common. They need time to work and have to stay wet to stay active. Depending on the type and thickness of the sealer being removed, multiple stripper applications and hours of dwell time may be needed. Once strippers dry out they stop working. This is why most strippers are in gel form, because they hold better to most surfaces and they hold in moisture, allowing them to stay active longer. Today, you have a choice of environmentally friendly strippers, such as natural soy and citrus-based products, or the good old-fashioned methylene-chloride-based strippers that will take the skin off your fingers given the chance. While the environmentally friendly strippers are safer to use, they require more time to work. No matter what type of stripper you use, read and follow the manufacturer’s instructions. Be sure to protect anything you don’t want to strip, and be prepared for a pretty miserable job.

Here are a couple of tricks I have learned over the years that can make stripping easier:

Use a walk-behind scrubber or rotary floor swing machine with a soft- to medium-bristle brush to help remove all the stripper and sealer sludge. Protect the machine with plastic, and use brushes that are resistant to the chemical strippers.

Another method that I heard about from a contractor, tried myself, and found to be quite clever is to create a chemical stripper “cooker” using wet cotton sheets. First, soak the sheets in water and ring them out until they are damp. Apply a uniform layer of chemical stripper over the concrete surface and then cover the surface with the damp sheets. Make sure to get as much contact as you can between the sheet and the surface, pushing the sheet down into the grout lines and deep textures. Cover the damp sheets with a sheet of plastic, and seal the ends as best as possible to keep the moisture in. Let this sit for hours, and if all goes well, the active stripper will liquefy the sealer, and via osmosis, the sealer sludge will soak into the sheet, greatly reducing the cleanup required.

Excess Antiquing Color Causes Problems

2008-07-24T10:15:00.000-07:00

Question:
I have a pool deck in which the sealer seems to be flaking off and coming up in some areas. This is not an issue that we have dealt with before, so I am a little concerned. Can you let us know what is occurring and how we can remedy this issue?

Answer:
This is actually one of the most common issues we face with stamped concrete. It is in fact not a sealer issue, but rather the antiquing color that is causing the sealer to fail. The sealer failure can occur within weeks of application, but more often shows up 6 to 12 months down the road.

Imprinted concrete looks pretty bland and unrealistic without highlights or antiquing, which give the pattern definition and color variation. These highlights make the concrete look like stone, tile or whatever natural material the installer is trying to mimic. The highlights can be accomplished in a multitude of ways, with release powder being the most common. Other popular methods include stains, tints, dyes and colored sealers. Virtually any means of getting some contrasting color to stick in the depressions and textured areas of the surface will work. The problem occurs when too much secondary color is present. The depth and type of texture on the imprinting tool will determine the amount of secondary color to use. More aggressive textures with deep grout lines, lots of deep veins, and rough slate or stone surfaces will accommodate more secondary or antiquing color. The opposite holds true for light textures with smoother surfaces and non-aggressive patterns. A good rule to work by is that secondary color should make up 5% to 30% of the final color. In your case, however, the secondary color makes up almost 100% of the surface color.

The real curve ball is that stamped work with such high ratios of secondary color can look amazing and beautiful. Once sealed, the work looks great, the applicator gets paid and everyone is happy. The problem is that you have ticking time bomb, and it is just a matter of time before it explodes. Have you ever considered what secondary color is made of and how it works? No matter whether you use release powder, stains, washes or tints, you are filling the surface pores of the concrete with solid material. Those solids are filling the voids that the sealer needs to fill in order to “bite” or adhere to the concrete. The more secondary color present, the bigger the problem. The sealer will encapsulate the solid color in an attempt to do its job, but if there are no pores to fill, adhesion is compromised, which leads to failure when external forces exceed the ability for the sealer to hold. This is usually why we see these types of failures in the spring, after a winter assault of freeze-thaw cycles, deicing salts and snow shovels. As a result, the sealer lifts up in small circular areas and takes the secondary color with it, since the color is all it had to hold onto. You are then left with a stamped slab that has round, discolored spots. The “discoloration” is actually the base color that should have been visible in the first place, but was covered with too much secondary color.

The repair is fairly simple in theory, but more difficult in practice. The sealer has to be chemically stripped, but the process will usually remove most of the secondary color as well. Once the stripping is complete, you can remove any residual secondary color, give the surface a good cleaning, and then allow it to dry before resealing. The hard part is selling the client on the new “correct” color combination of their patio. What was mostly dark brown with hints of tan is now mostly tan with hints of dark brown.

A good rule to work by is that secondary color should make up 5% to 30%
of the final color. In this case, the secondary color makes up almost 100%
of the surface color, causing sealer failure.

Is it OK to Restain Acid-Etched Concrete?

2008-06-06T11:31:00.000-07:00

Question:
I applied a concrete stain to a large 8-year-old concrete patio in Reno, Nevada—an area subject to somewhat extreme temperature variations. I initially washed the patio with a mix of muriatic acid and water to clean it. I hosed it off, waited a day or so, and applied the stain with a sprayer, following the manufacturer’s directions. Two years later, the patio now has areas of peeling. I would like to restain the whole patio again to make the color more uniform. I have heard that if you have washed a patio with muriatic acid, you cannot acid stain it. I am trying to find an expert who can tell me how to properly prep the surface, apply the stain and protect it. The stain I initially used was an acrylic.

Answer:
The product you used—a tinted acrylic stain—is not an acid-based concrete stain. It is a translucent concrete paint and is topical, which means it forms a colored coating on the surface of the concrete that will wear over time if not maintained. The surface preparation for these types of stains usually requires acid etching to open the surface to allow the acrylic to adhere to the concrete. But once concrete has been acid etched, the ability of a true acid stain to take is diminished. You will need to do a test to see how the acid stain takes to get a true indication of color and effect.

As far as your particular situation, you should strip off the remaining acrylic stain and clean the surface with soap and water and a clean water rinse. After the area dries, apply the stain, following the directions provided by the stain manufacturer. If you’re concerned an acid stain won’t take, you may want to reapply the same acrylic stain after cleaning the surface. No matter the stain you use, protecting it with a sealer and proper sealer maintenance will be key to keeping the stain looking good. In your area, plan on resealing every 12 to 16 months.

Humidity Can Cause Moisture Problems

2008-05-23T13:43:00.000-07:00

Question:
Chris, I am doing a stained concrete project using an acetone-based stain. I plan on sealing the stained concrete with a water-based urethane. This is a large 8,000-square-foot floor in the cafeteria of a local manufacturer, and it receives heavy traffic. I just completed a moisture test (using a calcium-chloride test). I did three tests, with results that ranged from 6.13 to 6.58 pounds. But I understand the recommendation is no more than 4 pounds. This floor is on grade, and the concrete is over two months old with a vapor barrier under the slab. The interior humidity has been high (around 70%) due, I think, to rainy weather and wet drywall mud.

Here is my question: Because of the high moisture readings, should I do this job? Is 4 pounds a strict guide, or are there some tolerances? For example, is 6.58 pounds acceptable but something higher, like 12 pounds, too high? This is the first time I have done a test like this.

Answer:
According to the ASTM standard for conducting a calcium-chloride test (ASTM F 1869), a reading above 4 pounds—the amount of moisture flow in pounds per 1,000 square feet over a 24-hour period—is considered a no-go for sealing. This is especially true for nonbreathable coatings, like the polyurethane you plan to use. That being said, you have a slab that should eventually drop below 4 pounds because of the vapor barrier.

You hit the nail on the head in regard to humidity. This is a very real environmental factor often missed when contractors prepare to seal, especially interior floors. Concrete is a sponge, and if conditions are right it will absorb and hold moisture, both in liquid and gas forms. The process of osmosis now comes into play—the movement of a liquid or gas from an area of high concentration to low concentration until balance is achieved. If the air above your floor has a high concentration of water vapor, or humidity, then the concrete will absorb moisture until it contains water equal to what is in the air. The practice of closing doors and windows to “dry-in” a room or building can actually trap moisture and create a steam room of sorts, making the problem worse or creating a problem where one didn’t exist. Drywall mud, paint and rainy or hot, humid weather can cause high moisture contents indoors, which will cause concrete to absorb moisture. This moisture will stay in the concrete until the moisture content of the air above the slab abates. Whether the humidity is manmade or natural, it can cause short-term high moisture readings, especially in the spring and fall, when days are warm and nights are cool.

Wait for a dry spell, open as many windows and doors as possible, use a fan to move air across the floor, and take another test after 24 to 36 hours of drying. If the HVAC system in the building is operational, run the air conditioner to help remove moisture. When the moisture readings drop low enough for you to seal the concrete (at or below 4 pounds), apply the sealer in the afternoon or evening, when humidity is lowest.

Using a Microtopping and Stencils to Rejuvenate Ugly Concrete

2008-04-18T08:21:00.000-07:00

Question:
I have a poured concrete walkway that is sound but worn and ugly. I have gotten quotes for overlaying it with brick or flagstone, but both will raise the level of the walkway too high (people will trip) and they cost too much. What can you suggest for a thin overlay material that looks like brick or flagstone, will not crack, will wear well, won’t be slippery, and I can install myself without exotic tools. (I’m a handyman, but not a professional builder.) I am located in the Northeast, so the concrete is exposed to freezing temperatures and snow shoveling.

Answer:
Even if you’re a do-it-yourselfer, I recommend that decorative concrete applications be left to the professionals. But since the existing concrete is in sound condition, you might consider overlaying the surface with a microtopping and using a stencil to create the brick or flagstone pattern. The overlay will be about 1/8 inch thick and can stand up to freeze/thaw conditions if applied and maintained properly. The application is pretty straightforward, and you have dozens of overlay colors and stencil patterns to choose from. Proper surface preparation and making sure no water can get under the overlay are the most critical factors in ensuring long-term performance. For proper installation instructions, refer to the guidelines provided with the product you select. For more information about overlays and stenciling, visit: www.concretenetwork.com/concrete/concrete_resurfacing
www.concretenetwork.com/stencil-concrete

A microtopping used with a stencil is a great way
to give old concrete a new decorative surface.

Never Apply Integral Color to the Concrete Surface

2008-04-11T08:02:00.000-07:00

Question:
I just purchased a home with a concrete patio that was poured 5 years ago. I was told by the previous homeowner that the person who poured the concrete added the color by hand, sprinkling it on top after the pour. The color was not mixed in with the concrete. He used 1-pound color packs that are supposed to add color to a 60-pound bag of concrete mix. The color is uniform, but every time we step on the patio, the color comes off on our shoes and appears to be flaking away. The concrete surface also appears to be somewhat soft. When moving a table the other day, I noticed that when I dragged it across the patio, it etched into the concrete. I have tried sealing the surface, but the sealant doesn't stick in all areas. What are my options? Is there anything I can do to prevent the flaking and rubbing off of the color, or do I have to remove the entire patio?

Answer:
The color packs that the contractor used are designed to integrally color concrete rather than be cast onto the surface. Integral color should never be used as a surface-applied colorant. It has no binder, so it must be mixed in with the concrete to “lock in” and bond. If it’s applied to the surface, there is no way to get a strong bond between the color and the concrete. That’s why the color on your patio is flaking off and the surface is weak. The proper product for surface application is a color hardener, which contains color, sand and cement and is broadcast on the surface and worked in while the concrete is still wet. Color hardener will actually produce a stronger surface because of the additional cement and sand contained in the product.

In this case, there is no way to strengthen the soft top layer. And applying sealer to the surface is like sealing over dust or dirt. The sealer is clinging to a weak layer, which is why it’s not adhering. You don’t need to remove the entire patio, however. The best approach is to use a power washer or grinder to remove the soft top layer until you get down to solid concrete. After removing the top layer, you can keep the concrete gray or use a microtpping overlay or stain to add back some color if desired. You can learn more about staining or overlays on The Concrete Network. Go to:
www.concretenetwork.com/concrete/concrete_resurfacing
www.concretenetwork.com/stained-concrete

Soft, flaky surface caused by improper broadcasting of
integral color on top of the concrete, rather than mixing it in.

Leveling a Floor with a Colored Overlay

2008-03-21T08:00:00.000-07:00

Question:
My wife and I are building a home on St. Croix, in the U.S. Virgin Islands. The floor was poured some time ago, and is rough and uneven. We plan on mixing a concrete slurry to level the floor. Is there a pigment we could mix in with it to color the floor? Also, the exterior walls of the home will be plastered in a couple of weeks. Is there anything you can recommend mixing in with the plaster that would color and seal? The home is on a knoll about half a mile away from the sea.

Answer:
There are multiple flooring products that can be used to even out a rough or unlevel floor. A self-leveling overlay is the most common, such as SD-T, Dayton Levelayer and Mapei Ultratop. These overlays go down at thicknesses ranging from 1/4 to 3/4 inch, and they self level with very little troweling or spreading required. However, there is an art and level of experience required to get a nice uniform finish, which will be especially important if this is going to be your final surface. Most self-leveling products will accept inorganic (iron oxide) pigments at low dosings. Consult the manufacturer of the specific product you are using for coloring guidelines.

I would stay away from mixing up your own concrete slurry. Unless you plan on modifying it with polymer, it will become brittle and crack. If you do not want to go the self-leveling route, use a microtopping product – a thinner overlay applied at a 1/16- to 1/8-inch thickness. Examples include QC Concrete Resurfacer HD and Miracote MPC. Depending on the type of finish desired, you can use a trowel, squeegee or roller to apply a microtopping. Most products can be colored integrally to almost any color desired.

As for coloring the plaster, you can use the same iron oxide pigments mentioned above to color any cement-based material, including plaster and stucco. But these pigments will do nothing in regard to sealing, so a separate sealer will need to be used as a finish coat. My advice is to use a precolored synthetic plaster or stucco product, such as Synergy StuccoBase Premix. These products are best suited for exterior walls.

Efflorescence Discolors Memorial Wall

2008-03-14T11:28:00.000-07:00

Question:
We built a veterans’ memorial last year and used a color additive in the concrete. Since our dedication ceremony, the color appears to have leached out, leaving a whitish limestone-like appearance. I have attached pictures to give you an idea of what we are up against.

Answer:
This is a classic case of efflorescence – calcium-based scale leaching to the surface of the concrete. This is a natural process and occurs in all concrete. (See my blog entry “Efflorescence on Black Concrete” to learn more about how and why efflorescence occurs, as well as how to eliminate it.)

In regard to this particular case, the best way to proceed is to clean away the efflorescence and seal the concrete. Cleaning can be accomplished with a very dilute acid (40 parts water to 1 part muriatic acid) or even better, a non-acidic efflorescence remover. (Check out Prosoco for more information on these types of cleaners.)

No matter the cleaning chemicals used, apply the solution directly to the affected area and scrub lightly to loosen the white salt residue. Rinse the area with clean water. Let the surface dry thoroughly, then seal. I recommend using an impregnating waterproofing sealer to stop the movement of salts to the surface. It can be any type of silane, siloxane or silicanate, available at most concrete material or stone distribution centers. If you want to darken the concrete color or give it a glossy appearance, apply a low-solids acrylic sealer as a final coat. The most important step with this project is to seal the concrete once the surface is clean and dry. If no sealer is used, the efflorescence will reoccur and in six months the wall will look white again.
In closing, thanks to you and all your members for their service to country and community!

A classic example of efflorescence, and the whitish discoloration it can cause.

Cause of Dull Spots in Sealed Floor

2008-02-29T14:43:00.000-08:00

Question:
Four years ago I covered my basement floor with a patterned overlay (I am in the decorative concrete business). I applied a two-part polyurethane sealer to it. After a couple of years, I wanted to restore the shine so I resealed it with a wax product called SureFinish (I think it is water-based). Over the course of a few months, the floor looked more and more dull in spots, especially where walked on with wet shoes. I stripped the floor with a mild muriatic acid cleaner and applied an acrylic solvent-based sealer, thinking that I needed the solvent to restore the color. The floor looked great at first, but after about a month it began to dull again in spots. When I wash the floor it looks great, but the dull spots show up when it dries, and over time I’m getting more and more spots. Do you know why this is happening? Is it perhaps because the original sealer was a polyurethane that the others sealers are not bonding to, and with washing and water exposure, they are coming off? How do I now reseal over the original sealer?

Answer:
I think you are on the right track in terms of the other sealers not bonding to the original polyurethane sealer. Now you have multiple layers of different sealers, all of which seem to be wearing. Applying a water-based wax and then a solvent on top was also not a good idea.
What is probably happening is diffusion. Where a sealer coat starts to come off, light no longer travels through it but instead diffuses, resulting in dull or white and hazy spots. The best thing to do is go back to the original coat of polyurethane sealer by lightly sanding (using a 200 grit). Then apply very light coats (800 to 1,000 square feet per gallon) of the wax. Test this remedy in a small area first to make sure it is working.

The Best Method for Stripping Sealers

2008-02-15T14:37:00.000-08:00

I recently spoke at the World of Concrete in Las Vegas on the topic of troubleshooting decorative concrete. During the Q&A session, a popular subject was stripping sealers, specifically what is the best way to go about it and what are the best products on the market to accomplish the task. So this installment will deal with just those questions.

Before deciding the best way to remove a sealer, you need to know what type of sealer you are stripping. Obviously, not all sealers are alike. Thicker sealers (polyurethanes and epoxies) perform better, but they will take longer to remove than thinner sealers (acrylics).

There are two general methods for stripping sealers: chemical and mechanical. Chemical strippers utilize chemicals to break down the polymer structure of a sealer. They permanently destroy the sealer, typically turning it into sludge. Mechanical removal of sealers involves using equipment to grind or blast off the sealer. Shotblasting, bead blasting, scarifying and grinding are common mechanical methods for sealer removal. The important thing when using mechanical means to remove sealers is to avoid damaging the substrate below. This is where you should use softer shot or beads, like finely ground corn husks or seed hulls.

By far the most popular and effective method of removing any type of sealer is to use a chemical stripper. This is especially true with decorative concrete, since maintaining the profile and color of the concrete is critical. Chemical strippers have undergone a major transformation in recent years. The desire for more environmentally friendly chemicals has led to the creation of a new family of strippers that are easy on the environment. These include citrus and soy-based strippers that use natural esters and oils to break down the sealer. These natural strippers have little impact on the environment, but they take longer to work. More aggressive chemical strippers based on methylene chloride work much faster. These strippers have been used for years to remove coatings and paints, but they are volatile and potentially hazardous—to both the environment and the applicator. So it really comes down to time vs. environmental impact and safety.

The process of stripping by chemical means requires time and keeping the stripper active, or wet. Chemical strippers only work when they are active. Most strippers are in a gel form, which helps keep them active longer. The slower-acting natural strippers require more time to work and thus keeping them moist is critical. A great trick to keeping a stripper active is to cover the stripper with a damp cotton bed sheet. The thin, damp covering will keep the stripper moist and help to absorb the dissolved sealer for easier removal. This process may need to be repeated, depending on the sealer type, stripper type and surface. Stamped concrete, with its texture and grooves, is by far the most difficult surface to strip.

Once the sealer has dissolved, a good cleaning will be necessary after stripping, even if a bed sheet was used to pull up the sealer. Remove the sludge with high-pressure warm water followed by cleaning with soap and water to remove any remaining residue. A clean water rinse, followed by plenty of drying time, is critical before reapplying a new coat of sealer.

Carpet Glue Residue Causes Sealer to Bead Up

2007-12-14T14:21:00.000-08:00

Question:
I pulled carpet from a room and then cleaned the underlying concrete floor at least eight times with a trisodium phosphate (TSP) solution. I also used a product from Home Depot called Jasco (a no-rinse TSP substitute) to clean the hard-to-remove glue. I washed the floor several times with water and let it dry. Next, I applied two coats of Kemiko stain with a garden sprayer followed by three coats of Chem-Coat sealer, applying it as directed with a lamb’s wool mop and allowing it to dry between coats. Finally, I applied a Chem-Coat protective finish. The floor came out beautiful, but after it dried I saw a small area of the surface where it looked like the sealer or finish coat did not take. It appears as beaded-up water and does not shine in that area. I would like to correct the problem because it’s noticeable, but I don’t know what to do. Can you offer suggestions?

Answer:
Carpet glue is some of the most stubborn stuff out there. I am impressed that you took so much time to clean it off. Most stain applicators I know would just place a microtopping over the concrete and stain the microtopping vs. taking time to strip off large areas of glue residue.

As far as the sealer beading up, it sounds like some remaining glue residue is causing "fish eyeing.” This phenomenon occurs when chemical contamination interferes with the sealer’s ability to wet out (i.e., penetrate into the surface). My suggestion is to apply several coats of finish wax to even out the gloss. If that doesn’t do the trick, you may have to go back and strip and reclean that area. This is a messy, time-consuming job and there’s no guarantee it will solve the issue. Usually the application of floor wax does the trick.

Sealers for Underwater Exposure

2007-12-07T14:20:00.000-08:00

Question:
We are installing a concrete garden fountain, and I plan to stain it myself. What are the best stain and sealer products for this type of project, and what maintenance is required?

Answer:
I am not a fan of stain and sealer on surfaces that are often wet or come in continuous contact with water. Unless you use a sealer designed specifically for constant water contact, you will have performance issues like haze and whitening and eventual failure. Sealers that can handle constant water contact are usually high-end epoxies, polyurethanes and polyureas. Before using one of these products, make sure it’s designed to be used in conjunction with a stain or tint.

We have seen concrete in continuously wet or underwater conditions colored successfully with just an acid stain or UV-stable tint or dye, with no sealer. If you go this route, make sure to use a product that is not water-soluble. Otherwise, the water will leach out the color over time, leaving you with plain gray concrete.

No matter what route you take, annual maintenance will probably be needed. This will include resealing (if you use a sealer) or at least removing white mineral deposits left on the concrete from hard water. A standard over-the-counter household bath scum and mineral remover works well in this situation.

Bad Concrete Causes Decorative Disaster

2007-11-09T15:23:00.000-08:00

Question:
I hope you can give me some idea about what’s going on with my concrete pool deck. The deck was poured in August 2005 by a local contractor, who then stamped the concrete in an Ashlar slate pattern using a dry color release. After he washed off the residual dry color from the surface, the deck did not look evenly colored. Some areas had barely any color while others had too much. I told the contractor that the color was unacceptable and needed to be fixed before the sealing. Despite that, when I wasn’t home the contractor went ahead and applied a sealer pigmented with a dark brown stain. That made the deck look even worse, but it isn’t my biggest problem. After the first winter, which was mild for the central Midwest, the decorative surface of the deck started to peel and chip away. In some large areas, the surface came off completely, down to the aggregate. I did not apply deicing salts, and no water was left lying on the surface.

Answer:
Unfortunately, you have a slab of decorative concrete that’s in bad shape and beyond easy repair. As the photo clearly illustrates, the top 1/2 to 1 inch of the concrete surface is beginning to come off because the stone, which gives concrete its strength, is pushed down, leaving a weak sandy layer on top. Once the top surface has been breached, it’s just a matter of time before the entire top will break apart. Because the layer below with the stone showing appears to be strong and intact, you have two repair options: totally rip out and replace the slab or remove the top 1 inch and cover the underlying concrete with a stamped overlay.

In my opinion, the problem is not caused by the contractor’s coloring methods. Instead, it’s probably due to poor installation techniques, poor curing, a bad concrete mix or a combination of all three. Stamping the surface of bad concrete only speeds up the deterioration process. What makes things worse is that the contractor is refusing to take any responsibility and will not get involved to help figure out what happened.

This stamped concrete patio is flaking away due to a surface
layer of weak concrete.

Removing Bubbles and Roller Marks in a Sealer

2007-11-02T07:00:00.000-07:00

Question:
I recently applied a two-component, high-solids aliphatic polyurethane sealer to a stained floor in a spa. First, I applied the primer coat with a roller and then applied the polyurethane, which has a longer pot life, with an airless sprayer. While applying the primer on the first half of the floor, I could see roller marks and bubbles and the primer started to string up on me. I mixed a new batch and proceeded to finish rolling the rest of the floor but at a much faster pace, and I seemed to have no problem. But now roller marks are visible throughout the entire floor, not to mention the bubbles.

To remove the bubbles, I was told by the sealer manufacturer to go over the floor with a floor buffer or 150-grit sandpaper and then seal again. But will buffing be aggressive enough to take out the marks? Also, should I apply the primer using a sprayer instead of a roller, and should I mix smaller amounts of the sealer? I think I may have rolled on the primer too fast producing the roller marks. What do you recommend to fix the issue?

Answer:
Sanding will take surface bubbles out, but buffing with a floor machine will not be aggressive enough. If the bubbles go deeper than the surface, you may need to strip and start over. My suggestion is to try sanding out the marks and then reapply your topcoat. If this does not work, strip down to a point were no roller marks or bubbles appear and start over. Do a test area before doing the entire floor.

I am not a fan of rolling in general, especially heavier bodied materials like epoxies or polyurethanes. All rollers produce lines, with more material coming off the ends of the roller as it moves across the surface. Depending on the material used, application temperature and pot life, the roller lines may or may not even out. The speed of rolling, the amount of material on the roller and the weight pushing down on the roller also play a role in leaving roller marks. Picture a car tire that has mud on it. If you drive slowly, the mud comes off the tire evenly. If you speed up, the mud flies all over and leaves more prominent marks on the outside edges of the tire. Heavy-bodied materials are always best applied in small batches and with a push-pull applicator such as a lamb’s wool or micro-fiber pad or a T-bar.

Overlays Over Wood Surfaces

2007-09-28T07:26:00.000-07:00

Question:
We have experience resurfacing concrete with microtoppings and polymer overlays, and we are now just starting to do this process over wood—either interior floors or upper-level patios that do not have enough clearance for concrete. What is the best practice for this process?

We currently staple down a vapor barrier, screw down metal lath, and then incorporate some fiber mesh into an underlay material about a 1/4 inch thick. After this sets up, we apply the microtopping or stamp mix to the required depth to take the stamp imprint and then spray apply antiquing color, acid stain or dye. This is followed by application of a high-traffic water-based sealer.

We have had two overlay failures; one cracked and the other leaked. What could be the problem? Also, can you recommend dependable products to use for the vapor barrier and the metal lath?

Answer:
From what you wrote, I have no issues with the surface preparation and systems you are using. I typically tell people to prep a wood or non-concrete surface as you would for tile: place a mortar bed with lath (as you are doing) or use cement board (such as HardieBacker) with seams taped and mudded.

As to your problems and questions:

-Did you cut any control joints into the surface? Cracks are caused by stress or movement. Just because it is a microtopping over a mortar bed does not mean it will not shrink or move due to stress and temperature. I would not be surprised to see that the crack had followed a seam in the plywood or decking in the subfloor. Utilizing control joints along long seams or large areas is important. Another thing to consider is the stability of the wood deck or floor. Additional bracing or stabilization may be needed, especially on exterior raised decks.

-A step often missed when installing exterior overlays is caulking. Water is amazing in its ability to migrate through a solid surface, usually finding its way through cracks, seams and edges. I recommend caulking or grouting all saw cuts and control joints. I would also caulk all the edges where the overlay comes in contact with a wall or another edge—pretty much anywhere water can get under or around the overlay.

-As far as a water barrier, I recommend using roofing felt or tar paper. And don't forget to tape your seams. Avoid using flexible rubber-based materials. The more rigid the better. A cement-based waterproofing mortar is also a good option. For metal lath, a stucco-grade material is fine. I have seen anything from chicken wire to concrete wire mesh used successfully.

Eliminating the ‘Squeeze’

2007-09-21T07:18:00.000-07:00

Question:
When we are stamping, we sometimes end up with a lot of crusting that we try to roll out or hammer away the next day. Do you have any tricks or suggestions for dealing with this type of problem?

Answer:
I assume you are talking about the material that pushes up between stamp imprints. If so, this is usually referred to as "squeeze." You will always have some squeeze, but it should not be overwhelming. If you are getting too much, here are a few things to look at:

Is the surface too wet? A wet surface can create more squeeze. Wait until the surface is a bit stiffer.

Are you using imprinting tools with lots of edges and angles? Tools with multiple edges (random stone patterns are the worst) tend to create more squeeze because it’s harder to hold multiple edges tight during stamping vs. one or two edges.

How old are your tools, and do the edges fit together tightly? Not all tools are built the same way, and if the edges don't come together tight, you will get more material pushing up between them.

To get rid of squeeze, the easiest method is to roll it out with a touch-up wheel or chisel while the concrete is still green. If you wait and come back after the concrete is hard, you can remove the squeeze with a good set of straight-edge metal chisels. The problem with waiting until the next day is that the areas exposed after breaking off the hardened material are now usually a different color and will need to be touched up with a tint, stain or colored sealer.

SEALER SERIES Part 9: Sealer Application Tips

2007-08-31T07:37:00.000-07:00

Each type of sealer has a recommended applicator and coverage rate, as discussed in Part 8: Choosing the Best Applicator. But simply using the right application tool won’t guarantee good results. You also need to practice the proper application techniques to avoid bubbles, blisters, lap lines and other eyesores.

The most common application problem is applying too much sealer at once (remember the phrase “thin to win”). Sealers are designed to perform best at a specific thickness, depending on the type of resin. This is determined by the coverage rate for that particular sealer. A good analogy is to compare sealers to a deck or cards. The first and second cards dealt are close to the surface, hard to pick up and very stable. The more cards you put on the pile, the more unstable the pile gets. The same holds true for sealers. The first and second thin coats are very stable, have good adhesion and provide good durability. The more you apply, either in one or multiple applications, the more unstable the system gets. With solvent-based systems, the signs of overapplication are typically bubbles, blisters and white haze. With water-based systems, you’ll often see blisters, foam and a milky white cloudiness.

Another common application mistake is lap lines, or uneven application. When applying sealer, always go back over the previous pass about 2 inches as you move across the surface. This overlap needs to occur when the sealer is still wet, so the two passes blend and become one. If the first pass dries, the second creates a lap line and can be seen after the entire floor is dry. Fixing the problem usually requires applying another full coat of sealer.

When applying sealer by sprayer (whether using an LPHV, airless or pump-up type) make sure to maintain constant pressure and use the proper tip. A cone-shaped spray pattern is better than a fan pattern, and the more atomized the sealer the better.

When applying sealer by roller, make sure to buy a roller suitable for the sealer type (water- or solvent-based) and a nap thickness appropriate for the surface. When rolling on water-based sealers, be careful not to over-roll, which can causing foaming and blisters. You also may need to dip the roller more often. Some newer acetone-based fast-drying sealers can’t be roll applied because they flash off too fast.

When using a lamb’s wool applicator, micro-fiber applicator, synthetic mop or T-Bar, the application process is the same. Pour the sealer on the surface, and push and pull the product while maintaining a wet edge until you achieve the desired thickness. These application methods are very good for water-based sealers because they don’t foam and you can see the white sealer go clear as you push and pull it around the floor. However, they will only work on smooth floors.