Sullivan's Blog

To Overlay or Not to Overlay

2007-03-14T11:43:00.000-07:00

Question:
I am getting ready to resurface concrete in front of two double garage entries. I have been told to have the concrete resurfaced with an acrylic overlay. But I have an estimate from a contractor to resurface using a cement-based overlay. I don't know which type of overlay to use or if an overlay is even the best remedy in this situation. Please help.

Answer:
The first question needs to be: What is the end result you are trying to achieve? An overlay will work in this situation, but so could other less costly methods. I am going to assume that you have settled on using an overlay because the existing driveway is damaged or has flaws that need to be covered. But if you only desire to dress up the surface, many different types of stains and solid-color toppings are available that will do just that. The important thing to remember is that these toppings just change the color of the existing concrete and will not correct the profile or hide damage.

If the concrete needs a new surface, a thin-section overlay, often called a “microtopping,” is a good choice. As with any overlay, surface preparation is the most important factor. A clean, properly profiled surface is critical for good adhesion. Other important factors include selecting the right material for the job and hiring an experienced applicator. Not all overlays are designed for exterior use. Ask to see a spec sheet for the product being applied, and feel free to contact the manufacturer to make sure the material will work in this scenario. No matter which direction you go, have your applicator provide references of previous jobs and a written warranty. Also ask to have all maintenance procedures and life-time performance expectations put down in writing before moving forward. A good applicator using a quality overlay material can provide a new surface that will last for decades.

Efflorescence on Black Concrete

2007-03-07T11:40:00.000-08:00

Deposits of efflorescence make black concrete look grayish-white.

Question:
Last week, we poured a band of integrally colored black concrete. It looked great for three days, but then it rained a little the night of the third day, and by the next morning all the black color had disappeared, hidden by a grayish-white surface discoloration. What happened, and how do I fix this?

Answer:
This is one of the most common but least understood phenomenons with concrete. Efflorescence is a chalky white salt residue that can occur with any product containing cement. As moisture migrates up to the surface of the concrete, it carries along with it calcium salts from within the concrete. When the salts reach the surface, they react with CO2 in the air and form insoluble calcium carbonate. This white, dusty, scaly salt can be minimal or dramatic, depending on the amount of free calcium salt present in the concrete. Exposure to rain, standing water, and sprinklers only make the situation worse, as water triggers the reaction and creates more efflorescence.

Efflorescence is not as noticeable when it occurs on gray concrete, but even a little efflorescence on colored concrete can be a contractor’s worst nightmare. Efflorescence makes red look pink, brown look tan, and black look gray or even white. The good news is that it will eventually go away on its own as the free calcium is depleted. The bad news is that this can take as long as 15 years. And in this situation, you can’t wait.

To fix the problem at this point, clean the surface with a mild acid or efflorescence remover (some manufacturers make special efflorescence cleaners) followed by sealing. To avoid the problem altogether on future projects, consider using a colored curing compound or cure and seal to match the color of the concrete. To learn more about efflorescence, read my other blog entries on the topic: Causes of Efflorescence on a Stamped Overlay and Efflorescence Hides Integral Color.

Avoiding a Dusty Mess When Removing Release Powder

2007-02-28T09:41:00.000-08:00

When cleaning release powder from concrete surfaces after stamping, removing and disposing of the residual powder is always a dusty and dirty mess. During one of my seminars on troubleshooting decorative concrete at the World of Concrete in Las Vegas, an audience member shared the following trick for removing release powder without the mess. I was so intrigued by the method he shared that I recently tried it, and can report that it works great! I never caught the gentleman’s name, so I can’t give him the proper credit for such a creative and helpful hint. Whoever you are, thanks!

Take any fine-grade silica sand, and mix with water to create a heavy, stiff paste. Apply this paste randomly to the stamped surface. Then with a stiff broom or walk-behind scrubber, scrub the surface with the sand paste. The wet sand grabs the release powder, eliminating any dust, and also acts as a grit to help scrub the surface while removing the release powder. Depending on the color and amount of release on the surface, the process may need to be repeated several times to achieve the desired look. When I tried this method, one pass was all that was necessary to obtain a clean stamped surface. The sand containing the release powder can easily be washed off with a hose or power washer or left to dry and vacuumed up with a wet/dry vac.

Blotchy Spots of Gloss in a Sealed Floor

2007-02-21T09:36:00.000-08:00

Question:
I recently applied two coats of an acrylic sealer to a stained floor. After the sealer dried, the floor appeared blotchy, with some areas glossy and others not. What causes this, and should I apply more sealer to remedy the situation?

Answer:
If you were to look at a concrete floor under a microscope, you would see what looks like an endless range of plateaus and valleys. The number and depth of these plateaus and valleys is directly proportional to the finish of the concrete. A smooth finish has fewer of them while a rough finish looks like the Grand Canyon. When sealer is applied, it fills the valleys, but you may need to apply more than one coat depending on the finish of the floor. Typically when we see a floor that has blotchy areas of gloss, this means that some areas do not have sufficient sealer to fill the valleys. Applying additional light coats of sealer usually resolves this issue. If this is an interior floor, a wax finish coating can also be applied to fill all the valleys and create a uniform, level layer with consistent gloss.

Changing the Color of a Stamped Walkway

2007-02-14T09:21:00.000-08:00

What once was gray is now red with the aid of a solid-color acrylic stain.

Question:
How can I change the color of a stamped slab after it has been poured? The customer was not happy with gray and now wants a reddish-brown color.

Answer:
You can change the color of stamped work once it has been placed by applying different types of stains, tints, or dyes. The type of coloring method you use will depend on the look desired and amount of color changed needed. Here’s a handy guide:

-For minor color adjustment – Use an impregnating stain or diluted acid stain.

-For medium color adjustment – Use a full-strength acid stain, dye, or tinted sealer.

-For complete color change – Use an acrylic or solid-color stain.

When using any of these methods to change or adjust concrete color, be sure to profile the surface according to the product manufacturer’s recommendations to ensure proper penetration and adhesion. In addition, the surface should be completely dry and the temperature above 50 F and below 90 F.

Finally, no matter what method you use, always prepare a small sample for pre-approval by the client.

Release Powder Causes Streaking

2007-02-07T09:19:00.000-08:00

Applying release powder with a heavy hand or on a slab that is too
wet can result in streaking.

Question:
Why did I get black streaks on the surface of this stamped concrete slab after removing the residual release powder, and how do I get rid of them?

Answer:
As the photo shows, the streaks of black release powder appear to be oriented in the direction in which the powder was thrown. This often occurs when too much material is applied at one time or on a slab that is too wet. Hard, clumpy release powder can also contribute to streaking. Always roll or “fluff” the powder in its container before application to break up any clumps. Also take care to cast the powder evenly across the slab rather than downward.

Another consideration is proper dispersion of the pigment in the release powder. If the material is not mixed properly at the manufacturing plant, streaking like this can occur. Always retain the batch number or a sample of the material so the manufacturer can run a test to verify if this was the cause of the problem.

Removing these types of blemishes can be difficult. You can try lifting the streaks of powder by scrubbing with a dilute acid solution. Another option is to disguise them by applying a stain or tint.

Sealing Concrete in Cold Weather

2007-01-31T16:09:00.000-08:00

A white, milky haze can form when sealer is applied below its minimum
film-forming temperature – usually around 50 degrees F. The best
remedy is stripping and resealing.

Question:
Are there general guidelines I need to be aware of when sealing exterior concrete in colder temperatures?

Answer:
As a general rule, 50 degrees F is the minimum ambient air and surface temperature needed when applying most concrete sealers and coatings. All sealers and coatings have a minimum film-forming temperature, or MFT. When the temperature falls below the MFT, cross-linking does not occur and the sealer film does not come together properly. Typical signs that the sealer MFT was not met include white hazing, white dusting, and delaminating.

It’s easy to judge air temperature by looking at an accurate outdoor thermometer or getting a current local weather report. Obtaining surface temperature is a bit more challenging. I have found that using an infrared temperature gun is the best way to get accurate concrete surface temperature readings.

Another factor to consider when sealing concrete in temperatures at or close to 50 degrees F is the type of solvent the sealer is based on. Since temperature is a catalyst, the colder the temperature, the slower the sealer cures. When the weather gets colder, switching to a sealer that uses a faster solvent might help avoid problems. Water is the slowest of the solvents, so I would avoid use of a water-based sealer when outdoor temperatures drop. Acetone is probably the fastest solvent, so consider using a sealer with a high acetone content when sealing in cold temperatures. As an added note, spraying vs. rolling is always recommended when applying sealer in colder temperature because it leaves even, thin coats for the best possible cure.

I often hear from applicators who say they have been applying sealers successfully at air temperatures of 35 to 45 degrees F for years. Every project has different environmental factors to consider, thus the 50 degree rule is a suggested safe guideline. Those who choose to seal concrete at temperatures below 50 degrees increase their risk for failure substantially. Is it better to be safe than sorry? From the number of emails and calls I receive to help solve cold-weather sealer problems, I think safe. If a sealer fails because it was applied below the MFT, often the only remedy is labor-intensive and costly stripping and resealing.

Best Method for Coloring Step Faces

2007-01-24T16:02:00.000-08:00

Applying a paste made with color hardener is an effective, easy way
to color step faces. Using the same hardener that was applied to the
flatwork portions of the project helps to ensure color uniformity.

Question:
When stamping and coloring a set of steps, how do I get the risers, or step faces, to match the treads and adjoining patio surfaces?

Answer:
This can be accomplished with dry-shake color hardener or integral color, but using color hardener often achieves the best results. When using integral color, timing is everything. No matter how smooth the surfaces of your forms, some toweling will need to be done to the faces once the forms are removed. This means removing the forms while the concrete is still wet enough to take a trowel and be imprinted, but not too wet so the stairs slump and lose shape. This can be a tricky proposition, depending on the number and size of the steps.

When using the color hardener method, you can pull forms the same day (with a much longer set time if desired) or after many days. When you’re ready to color the step faces, you mix the hardener with a concrete polymer glue – acrylic or polyvinyl acetate (PVA) work best – to create a paste that you apply with a trowel as if icing a cake. By roughening the step faces a little after removing the forms (a light broom finish works well) you provide a better surface for the color hardener paste to grab onto.

Note that with both methods, knowing the best time to imprint the concrete is important to achieving good results, so experience is critical. The water-cement ratio of the concrete is also important. Do not add water to the step faces when using integral color, as this will dramatically lighten the color. When using the color hardener method, strive to make the color hardener paste the same consistency and slump as the concrete was when the hardener was applied to the flat surfaces. This will ensure a more uniform color match to the flatwork areas. Be careful of using color hardener paste for step faces when integral color has been used on the rest of the project. There are many variables to control, so achieving a good color match becomes very difficult.

How to Achieve Color Consistency When Tinting Overlays

2007-01-17T14:28:00.000-08:00

Question:
I have not had much success tinting overlays on site with tint packs. What is the best way to tint overlays to ensure color consistency?

Answer:
The same basic principles apply when integrally coloring an overlay as when integrally coloring concrete. (See The Concrete Network article Understanding Colored Concrete Common Problems, Why They Occur, and How to Avoid and Fix Them.) The big difference is that the margin of error is much smaller when coloring a few gallons of overlay vs. coloring a large batch of concrete. The biggest factors to consider are batch size and batch-to-batch consistency. The larger the batch, the lower the chance for color inconsistency.

For the best results, tint or color the liquid component of the overlay mixture (water or polymer) in one large container. If you do not have a large enough container, “box” the liquid by pouring it back and forth between smaller containers until you feel you have mixed it multiple times and have achieved a consistent color. You can then measure out the colored liquid with a graduated measuring container to ensure you get the same amount of colored liquid in each batch. Here’s a tip: Cut a small hole in the side of your measuring container at the top of the liquid level to be sure you get the same amount in each batch.

Another important consideration is to use a reputable tint manufacturer that uses a batch number system, with retained material samples kept from each batch, so you can go have the color checked if you have a color issue. Remember to write down those batch numbers just in case!

Applying Water-Based Sealers

2007-01-10T14:22:00.000-08:00

Water-based sealers tend to foam and bubble after being applied with
a roller. Instead, use a micro-fiber applicator.

Question:
What is the best method for applying water-based sealers?

Answer:
Water-based sealers require a different method of application from traditional solvent-based sealers. Unlike solvent-based products, which are basically resins (acrylic, wax, polyurethane, etc.) dissolved in solvent, water-based sealers use a mixture of water and other chemicals to keep the dissolved resin in suspension. Because of this emulsion chemistry, these sealers tend to foam easily when applied by a sprayer or roller, resulting in lots of soap-like bubbles. Thus the best method of applying a water-based sealer is with a micro-fiber applicator or mop. Pour a puddle of the sealer directly onto the floor, and then use a clean, flat micro-fiber applicator to push and pull the sealer across the surface until you get a very thin film.

Be aware that the typical coverage rate for water-based sealers is 400 to 600 square feet per gallon, about 100 to 200 square feet more per gallon than with solvent-based sealers. That’s because water is slower to evaporate than a solvent, giving you more time to spread the sealer into thinner coats. As with any sealer, applying multiple thin coats is always recommended.

Fixing Cracks Before Overlay Application

2007-01-03T16:24:00.000-08:00

An epoxy crack filler, feathered 2 inches on either side
of a crack.

Question:
What is the best method for fixing cracks in concrete prior to applying a decorative overlay?

Answer:
The term “fixing cracks” is a bit misleading since there is no way to “fix” cracks in concrete, only fill them. The proper term to use when treating cracks prior to placement of a decorative overlay is “bridging.” This is accomplished by filling or covering the crack with a rigid material so it becomes flush or slightly higher in elevation than the surrounding surface. (Avoid soft, flexible crack fillers.)

To prepare the crack for repair, use a crack-chaser diamond blade to remove any loose concrete and to straighten out the crack as much as possible. The repair material filling or covering the crack needs to bond tenaciously to the concrete surface and be applied so that it gradually feathers down to surface level. The crack filler also needs to bond well with the overlay, so it needs to have a rough profile. The three most common methods for bridging cracks prior to applying a decorative overlay are:

-Rigid Epoxy Systems – These are usually two-part epoxies available in self-mixing cartridges or for mixing onsite. You apply them using an injection gun or putty knife to fill the crack to overflowing, and then you feather out the epoxy on either side of the crack anywhere from 2 to 5 inches (see photo). Placing mesh tape into the wet epoxy provides additional reinforcement. Once the epoxy begins to set, course sand is cast onto it to provide a rough bonding surface for the overlay.

-Cement-Based Systems – Polymer-modified cement-based repair mortars are mixed onsite and applied with a trowel or putty knife (again, using the feathering technique). Multiple thin applications are usually required to avoid shrinkage cracking. To provide a good bonding surface for the overlay, roughen the surface by scratching it with a broom or trowel as it begins to set.

-Crack Suppression Mats – These have been used successfully for years in the tile industry. Roll out the mat to cover the crack by 5 inches on either side (or cover the entire surface if cracking is extensive), and adhere the mat to the surface using a bonding primer or glue. This type of crack suppression method is also a great way to cover seams when applying decorative overlays over wood and other non-concrete surfaces.

No matter the type of crack treatment used, assuring that the crack is properly bridged is critical in eliminating shadowing and show-through of the original crack in your newly applied overlay.

Best Floats for Applying Color Hardener

2006-12-27T16:03:00.000-08:00

A resin hand float (top left) is often the tool of choice for working in color
hardener, vs. a magnesium float (bottom right).

Question:
Why is it recommended to use wood or resin floats when applying dry-shake color hardener?

Answer:
Wood and resin floats leave a rougher surface than magnesium or aluminum floats. The rougher concrete surface allows for more uniform moisture migration. Color hardener needs this surface moisture to react, or “wet out.” The hardener also needs to be worked into the concrete. The rougher surface of a wood or resin float provides better dispersion of the hardener and works it into the surface more evenly and consistently than a metal float. That said, using wood or resin floats to apply color hardener is considered best practice, not a hard-and-fast rule. There are many applicators who use metal floats successfully.

Dyes vs. Stains: What Are the Differences?

2006-12-20T16:01:00.000-08:00

Question:
I hear a lot about using dyes on concrete. What are they, and how do they differ from chemical stains?

Answer:
Dyes are the latest buzz in the decorative concrete community. Their ease of use, extensive palette, and vibrancy of color (which can be more intense than chemical stains) are creating a wave of popularity that is gaining momentum.

Unlike stains, which react chemically with the calcium hydroxide in concrete, dyes are nonreactive and impart color by penetrating concrete or other porous cementitious surfaces. Dyes are much smaller in particle size than chemical stains or acrylic stains, thus allowing for easier penetration and color saturation while leaving less residue on the surface. A good analogy for comparing the color intensity and penetration of dyes to stains is that you can fit a lot more marbles than bowling balls into the same size container. The small dye particles fill the pores of the concrete and are very hard to remove, making dyes nearly as permanent as stains. Because there is virtually no residue, minimal cleanup is required, greatly speeding the application process.

Dyes are available in water- or solvent-based formulations and produce looks ranging from monotone to translucent, depending on how they are applied. Water-based dyes typically produce more marbling and variegation (similar to the look of a chemical stain), while solvent-based dyes tend to be more monotone and uniform in color. Some manufacturers’ water- and solvent-based dyes can be combined to produce special color effects. The downside to dyes is that they penetrate very fast, leaving little room for error during application. Also, they are not UV stable, so most manufacturers recommend indoor use only.

I encourage you to try dyes and discover the unique effects you can achieve with this new coloring technology.

What is Chris Sullivan All About?

2005-10-18T10:40:00.000-07:00

Welcome to my Blog! My goal is to contribute to the betterment of the decorative concrete industry by getting down into writing informatiion about decorative concrete so it may be used by many people and hopefully improve the industry.

Here is an article on The Concrete Network which tells you more about myself.

Chris Sullivan: Helping Contractors Better the Decorative Concrete Industry

It was by chance that Chris Sullivan, National Sales Manager for QC Construction Products ( a leading manufacturer of decorative concrete systems), accumulated years of decorative concrete industry experience.

Armed with a degree in Chemistry from the University of Pittsburg, Sullivan started his first “real job” with Bayer Corporation, the single largest manufacturer of iron oxide pigments, in an obscure division working with those very pigments. There, Sullivan gained experience marketing, as well as working in the lab making samples, testing and doing color matches.

“It was a great way to start in the decorative concrete industry, a great backbone,” Sullivan recalls. After three years, he went into sales for Bayer in Denver, whre he sold pigments to block, paver, and specialty pre-cast manufacturers as a technical sales representative for the company.

Next, Sullivan moved into Bayer’s polyurethanes coating division in Los Angeles as a technical sales specialist. It was eight or nine years before the pieces all fit together—the sales and technical experience that formed the foundation of Sullivan’s job at QC.

“At the time, I had no idea this is where I was going, but I was getting invaluable technical expertise in the industry, which all came together when I got the job working with decorative concrete at QC Construction Products,” Sullivan says.

“When I started at QC, I lacked installation experience,” he admits. “So I volunteered to work with installers to learn that part of the job, and I did lots of reading and got dirty doing hands-on work.”

Sullivan started with QC as a district sales manager five years ago, before being promoted to regional sales manager, then National Technical Director. As Director, Sullivan is responsible for Colorado sales, as well as a handful of sales representatives that cover a larger area (the Midwest and the Rocky Mountains), answering technical questions, and working with corporate.
“I answer larger technical sales questions nationwide…the variety keeps it interesting and fun,” laughs Sullivan. Part of that variety also includes speaking about troubleshooting decorative concrete at the World of Concrete.

“Decorative is this offshoot of the concrete industry, there’s an artistic element, as well as engineering and science,” Sullivan explains. “I see a lack of experience—[some] contractors not reading directions, trying to cut corners...The processes for decorative concrete are unforgiving, especially when you cut corners or don’t follow guidelines.”

Sullivan adds that another pitfall is underestimating the schedule of the steps involved. “There tend to be a lot more secondary factors at play, such as temperature, humidity, dew point, and ventilation,” he adds. “These are all learned by experience…And reading directions.”

At the top of Sullivan’s list of things a contractor can do to keep on top of his game: continuing education. In his Concrete Network article “Avoiding Problems with Decorative Concrete Starts Early: Seven Steps to Success Before You Start,” Sullivan writes, “Continue your education as often as you can. Schools, seminars, and product demonstrations are available everywhere. Take advantage of them. Be aware though, not all are equal. Do your research before spending any money…Keep asking questions. Keep learning. Strive to be an expert on what makes you money.”

“[Everyone] needs continuing education to improve the quality of their work,” Sullivan explains. “Be an expert, get good at the basics. Understand the products. Do [your] research. The Concrete Network is a great [research] resource.”

Sullivan also recommends getting involved when attending training, rather than just sitting back and observing. “Get hands on,” he stresses. “On average, less then five percent [of contractors] get involved and do anything…This is not a qualitative industry. Don’t be afraid to ask questions and get dirty. People who ask and get involved succeed.”

Another key to success that Sullivan recommends is focusing on your specialty. “Don’t get carried away with the artistic side [of decorative concrete] before you have the basics mastered,” he advises. “Focus on what makes you money. For every high-end job, there are 50 basic jobs.”

Sullivan forecasts continued growth for the industry, with no sign of slowing up.
“Overlays have come on strong and will continue…There’s lots of grey, already existing concrete out there,” he says, adding that interiors with overlays will also see continued growth.

“All in all, the market is strong,” adds Sullivan. “[But] it concerns me that a growing number of people are getting into the industry, both contractors and manufacturers. Bad jobs affect the whole industry. One job mistake can turn 25 to 30 people off of decorative concrete.”

“Manufacturers want to get into it because they think there’s low cost to get in, but it’s very labor-intensive and service-oriented to be a good manufacturer,” he continues. “All in all, the industry has come a long way and there’s a lot of good growth to go. [But] it will take a lot of discipline from all parties.”

“I hate to see good jobs go bad, but there will always be variables and issues,” Sullivan concludes. “[That’s why] I like the chemistry and quantitative side of my job, solving problems, giving solutions.”

Which is why Sullivan is in the perfect position at QC, as well as in the decorative concrete industry.

Staining Basics

2006-08-24T08:44:00.000-07:00

After applying an acid stain, it’s necessary to scrub the concrete with an
alkaline soap to neutralize the concrete and remove any unreacted stain
and stain residue.

Question:
I install a lot of driveways and patios, and some of my new customers are asking for stained concrete. I’ve never tried applying acid stains. What are the basic steps, and how can I avoid problems?

Answer:
I get questions like this one almost every week, and not just from first-time stain applicators. When applying acid stain, understanding the basics are vital to achieving good results. Let’s review the four basic steps to staining and the proper procedures for each. Following these steps can eliminate most problems when staining concrete.

1. Surface preparation. Understanding what the concrete is going to do once the stain is applied is very important. Proper surface preparation can save you a lot of headaches down the road. A simple water test (spraying water over the surface and observing what happens) is always recommended and tells quite a bit about the porosity of the concrete and the ability for the stain to wet out and react. Look for dry spots or beading of the water. If the water does not soak in evenly, additional prep may be necessary. Dry sanding, chemical degreasers, and mineral acid cleaning are three common methods of cleaning or opening up the surface for better penetration. Conducting a moisture-vapor emission test is also a good idea at this time. This will measure how much moisture vapor is being emitted from the slab. Too much moisture could inhibit stain penetration. You can read more about this topic on The Concrete Network (www.concretenetwork.com/bob_cain/index.html).

2. Stain application. Applying the stain is actually the easiest of the four steps. Most stains provide a coverage rate of 250 to 300 square feet per gallon. Avoid overapplication, which can create surface tension or buildup, especially on less-porous concrete surfaces and when using darker stain colors. I recommend applying the stain using a broom or walk-behind scrubber to promote better penetration and reaction. Make sure the stain “self heals” after scrubbing, which means the brush or broom marks close up and the stain becomes one fluid layer. Allow a minimum of 5 hours of dwell time, and repeat the procedure a second time if a darker color is desired.

3. Neutralizing and washing. This is the most misunderstood and overlooked step of the four. To better understand the importance of neutralizing, think of it this way: By applying an acid stain, you take concrete from a basic pH state to an acid state. You need to return the concrete to a basic state, while removing any unreacted stain and stain residue. Simply put, this step involves a good old-fashioned cleaning and scrubbing with an alkaline soap that can break down stain residue and neutralize the surface. Using water by itself is not enough. Once again, use a broom or walk-behind scrubber. Typically, multiple scrubbings are needed, especially with terracotta and dark brown stains. Take a pH test to make sure the surface has been properly neutralized. Then rinse the surface with clean water and allow ample dry time before sealing.

4. Sealing and maintenance. The final step is to apply a sealer to the stained floor to keep it looking and performing its best. However, sealing by itself is not enough. It’s important to use a sealer system, which includes a base-coat sealer and a sacrificial topcoat sealer, or wax. (See the Sullivan’s Corner post [date?] on removing black heel marks.)

Even when you follow all the steps outlined above, variations can occur. That’s why you should apply a sample of the stain for all your staining projects. This is the only way to get a good idea of what the stain will look like. For more detailed staining guidelines, consult with the stain manufacturer. Also, visit ConcreteNetwork.com for articles and reference guides on staining and troubleshooting stain problems.

Plasticizer Migration Inhibits Stain Penetration

2006-11-09T11:09:00.000-08:00

Question:
I recently stained a 5-year-old concrete floor. The owner of the building had rubber mats down on the floor near the front entrance for 4 years. After staining, I noticed the stain was significantly lighter in color in exactly the same spot where the rubber mats had been. What caused this, and how can it be fixed?

Answer:
The cause is most likely plasticizer migration. Plasticizers are chemicals added to plastics, vinyl, and rubber to make them softer and more flexible. The softer or more flexible the material, the more plasticizer it contains. Since rubber mats are fairly flexible, they contain a lot of plasticizer. Over time, the plasticizers migrate out of the rubber or plastic and are absorbed into surrounding materials (in this case, your concrete floor). Heat and pressure can speed the process. Since concrete is porous like a sponge, plasticizers migrate into the pores easily, filling them with small amounts of plastic that inhibit the penetration of water or stains. That’s why on this project the stain was lighter only in those areas where the mats had been laying for years.

Unfortunately, removing plasticizers from concrete is very difficult. A good degreaser or stripper can be used if the problem is detected prior to staining. If stain has already been applied, a dye or color wash can be put down to help darken the color in the affected areas. If the area has already been sealed, try applying a tinted sealer. Be sure to soften the edges of the tinted sealer to avoid turning a lighter color problem into a darker color problem.

Advantages of Color Hardener vs. Integral Color

2006-11-22T07:27:00.000-08:00

Although color hardener must be applied by hand, the results are worth
the effort.

Question:
What is the proper application method for dry-shake color hardener, and what are the advantages of using hardeners instead of integral color?

Answer:
I get this question from time to time. While fairly basic, it addresses a bigger issue: Why do some stamped concrete contractors prefer integral color and stay away from using color hardener?

I am a big proponent of color hardener! Using color hardener produces a stronger, brighter, more durable concrete surface than using integral color alone. Still, contractors tend to avoid color hardener for two reasons. First, integral color is easier to use. No application is required, and there’s no mess. Just order it from your ready-mix supplier, and you’re done. Second, many contractors don’t understand how color hardener works, and thus are afraid to use it. That’s too bad, because using integral pigments limits your color options and puts you at the mercy of the ready-mix company in regard to color consistency.

Although properly applying color harder is a bit of an art form, you can take a lot of the guesswork out of the process by following these basic guidelines:

(1) Use the coverage rate recommended by the manufacturer. Coverage rates generally vary by color. Lighter hardeners typically require a heavier application to achieve full color saturation (about 3/4 to 1 pound per square foot) while darker color hardeners hide better so you often need to use less (about 1/2 to 3/4 pound per square foot).

(2) Apply color hardener while the concrete is plastic (wet) but most of the bleed water has dissipated. It’s better to apply the hardener a bit early than to wait until the concrete is too hard.

(3) Allow enough “wet out” time for the proper amount of moisture to wick up from the concrete and be absorbed by the color hardener properly. This step, though one of the most critical, is often overlooked by new color hardener applicators. Give the hardener at least 7 to 10 minutes to wet out before trying to float it into the surface. Running a float across the surface too early will cause tearing.

(4) Use a wood or resin float to incorporate the color hardener into the concrete rather than a magnesium or aluminum float.

I encourage all stamped concrete applicators to become competent at applying color hardener. Using hardeners not only expands your color palette, but also reduces color-related callbacks and produces a better surface finish.

Causes of Sealer Delamination

2006-12-13T15:44:00.000-08:00

A visual clue that a sealer is wetting out properly is a darker color where
it penetrates the concrete surface (left side). On the right, the sealer is
simply laying on top of the surface, with no penetration occurring.

Question:
What would cause a sealer to delaminate?

Answer:
There is no quick and easy answer, since most sealer failures are caused by multiple factors. However, one thing common to most sealer delamination failures is insufficient “wetting out” of the concrete surface. All sealers, even the membrane-forming types most commonly used on decorative concrete, exhibit some characteristics of penetration. What I call the “legs” of the sealer need to bite or penetrate into the substrate. These legs are what make contact with the concrete surface, and they need to penetrate, or “wet out,” the surface for proper adhesion of the sealer. If the surface exhibits some characteristic that prohibits this from happening, the sealer won’t lock into the surface and a weak film results.

Factors that can inhibit a sealer from wetting out properly include:

-A concrete surface that is too hard or nonporous, preventing the sealer from penetrating.

-A surface that is too cold or hot. (The ideal temperature range for sealer application is 50 to 90 degrees F.)

-Overapplication of the sealer, which creates high surface tension and surface buildup.

-Too much moisture present in the pores of the concrete, which reduces adhesion.

Note: The higher the solids content and gloss of the sealer, the harder it is for the sealer to wet out. Common practices for overcoming this problem are to use a compatible lower-solids sealer for the first coat or dilute the first coat of sealer. If you dilute a sealer, make sure you are meeting local VOC regulations because you are changing the solids content.

Banishing Blisters in a Stampable Overlay

2006-12-06T13:17:00.000-08:00

Question:
When I apply stampable overlays I often get blisters ranging in size from a dime to a half dollar. What causes these flaws, and how do I get rid of them after the surface has cured?

Answer:
When a dry cement-based mix of any kind is combined with water, it begins to react as it hydrates, giving off gases (CO2, H20, and others). Most concrete surfaces are porous enough during the finishing stages to allow for these gasses to work their way to the surface and escape directly into the atmosphere. Since stampable overlays are polymer-modified, off-gassing can be more of problem when compared to typical concrete. The polymer (plastic) creates a tighter surface when finished with a trowel. Finishing the surface too early or adding extra water or a finishing aid to help close up the surface can trap gas and create blisters. A second factor that can contribute to blister formation is failing to apply a primer to the substrate before overly application. Not only does the primer act as a glue to adhere the overlay to the surface, it also closes the pores in the substrate and prohibits gas transmission to the overlay.

To prevent blistering, wait a bit longer to finish the surface or cut back on the amount of surface moisture used to aid in finishing. Remember that stampable overlays are porous by nature. Trying to get a tight finish similar to what you can achieve with concrete is not feasible and can create problems, blisters being one of them. If you see blisters forming while finishing, use a sharp-pointed object to pierce the blister and then use a trowel to rework the material back into the surface. If you find blisters after the overlay has cured, try injecting the hollow areas with epoxy or remove the blister and fill the spot with the same overlay material, blending the edges to create a less noticeable patch.

The Color Purple – Why Does It Appear on Brown Concrete?

2006-11-29T13:13:00.000-08:00

These two pieces of concrete are from a three-day-old slab integrally
colored a medium brown. The piece on the right has a purplish cast
on the surface, while the piece on the left shows the true brown color
on the inside.

Question:
A day after pouring a concrete slab with a medium-brown integral color, the color looks more purple than brown. Why is this, and how do I get the brown color back?

Answer:
As discussed in previous entries of Sullivan’s Corner, the true color of concrete lies within (see photo). The purple color phenomenon you’ve observed is actually a surface effect resulting from one or a combination of factors. Concrete integrally colored a shade of brown (from light tan to dark chocolate) can take on a purplish cast due to efflorescence, a high water-cement ratio, or a rough surface finish (broom or sweat).

Luckily, this issue is easily remedied. A very mild acid wash (40 parts water to one part muriatic acid) or cleaning with a chemical product specifically for removing efflorescence often removes the purple cast and brings back the true brown color. Once the slab is dry and the brown color restored, apply a good sealer for long-term maintenance. To minimize the purple color phenomenon on your next project, I recommend using a concrete mix with a low water-cement ratio (consider adding water reducers or plasticizers) and apply a good-quality cure and seal or curing compound.

Hot Tire Marking on Sealers

2006-08-31T08:50:00.000-07:00

These black tire marks could have been prevented by using a different
type of sealer.

Question:
Why do car tires leave black marks on my sealed driveway? How do I avoid this and remove the existing tire marks?

Answer:
This is a phenomenon called “plastizer migration.” Plastizers are polymer compounds added to rubber, glue and plastic to make them flexible. The rubber used to make car tires contains plastizers to improve traction. But when the car is driven, the tires heat up, causing the plastizers to soften and leach out of the tire. When a hot tire is parked or driven on certain types of sealers, the plastizers migrate into and discolor the sealer. The better the tire quality, the higher the quantity of plastizer—and the greater the chance for hot tire marking. Lower-quality tires are harder and contain less plastizer, so they usually result in less hot tire marking on sealers.

If switching to harder tires is not in the cards, then consider using a different type of sealer. When a sealer cures, the resins cross link, forming a sticky tangle, like a bowl of undercooked spaghetti. All sealers exhibit some degree of cross linking. The greater the cross linking, the denser the coating and the more resistant the sealer will be to hot tire marking. Most hot tire marks occur on acrylic sealers, which exhibit minimal cross linking. Using a higher-solids acrylic or a high-solids, highly cross-linked polyurethane or epoxy sealer will reduce hot tire marking greatly. These sealers form very dense films that limit or prevent plastizer migration. Striking a good balance of sealer durability and density will make all the difference when sealing driveways and garage floors.

To get rid of discoloration from hot tire marking, cleaning the surface with a concrete degreaser may be all that’s needed, depending on the level of discoloration. If the discoloration has migrated deep into the sealer, you may need to loosen the affected areas with a solvent or totally remove the sealer with a chemical stripper.

Exterior Staining when Rain is Forecast

2005-11-10T10:06:00.000-08:00

Question:
I acid stained a driveway today and plan to return tomorrow to clean and neutralize the surface. We are expecting rain tonight. Do I need to cover the driveway with plastic or do anything to protect the surface because of the rain?

Answer:
The short answer is, yes! No matter what color acid stain is used, there is always excess stain (called “stain residue”) remaining on the surface. Acid stain residue contains some unreacted stain, which will discolor most anything it comes in contact with. If it rains, the runoff will carry some or all – depending on the amount of rain – of the residue with it. Darker colors tend to leave more residue then lighter colors.

Depending on where the runoff goes, this could be a small issue or a major problem. I have seen stain residue carried by rainwater runoff permanently discolor brick, sidewalks, stone, and vinyl siding. Covering the surface with plastic would help, but it is hard to keep rainwater from getting underneath and causing the same issue. Plastic can also affect the appearance of the stain where it touches the stained surface. If rain is in the forecast, either postpone staining or make sure the residue is cleaned off before the rain starts.

Improper Curing of Colored Concrete

2006-10-19T14:52:00.000-07:00

White haze is left behind after removal of a nonbreathable curing cover.

Question:
This integrally colored floor was cured with a nonbreathable curing paper. What are the white marks on the surface, and how do we remove them?

Answer:
A nonbreathable curing material will create a vacuum that sucks moisture from the concrete up to the surface. The moisture then has nowhere to go because it is trapped beneath the nonbreathable covering. Anything carried to the surface along with all that moisture (such as natural salts in the concrete) will be left on the surface as the moisture evaporates once the covering is removed.

The white haze on the concrete surface seen in the picture is dried salt residue, or efflorescence, that was left behind when the cover was removed. Nonbreathable curing membranes tend to create more efflorescence because of the dramatic vacuum they create when placed on wet concrete. A breathable covering is always preferred, especially on colored concrete.

In this case, using lots of water to remove the surface salts while they were still wet would have minimized the white haze. Now, however, multiple passes of a rotary scrubber with a scrubbing pad are needed to remove the deposits.

Base Color vs. Secondary Color

2006-06-29T16:21:00.000-07:00

For most decorative stamping work, lighter base colors are accented by
darker secondary colors. In this case, the results mimic naturally
weathered stone.

Question:
What is the difference between base color and secondary color in stamped or imprinted concrete?

Answer:
The base color refers to the primary color of the concrete. Most stamped concrete is colored with pigments that are either added to the mix (integral color) or surface applied (shake-on color hardener). While both are good methods of coloring concrete, color hardener provides greater color selection and enhances the strength and durability of the concrete surface.

Secondary colors are used over the base color as contrasting accents or highlights. The contrast is what makes stamped concrete come alive, and provides the perception of stone, tile, wood, or rock. There are many different products and methods for imparting secondary color, depending on the final look desired and the applicator’s preference. These include, but are not limited to, pigmented release powder, tinted liquid release, stains, tints, dyes, and tinted sealers. The most common, and arguably most practical method for adding secondary color to stamped concrete, is to use a pigmented release powder during the stamping process.

There is no limit to the number of base or secondary colors that can be used. In fact, blending multiple colors, in both the base and secondary applications, can add to the overall realism of the results. An important factor to keep in mind: The secondary color should make up no more than 40% of the final color you see. Anything more then that can impair the adhesion of the sealer to the concrete surface.

Can Too Much Stain Be Applied?

2006-10-05T08:49:00.000-07:00

Question:
Last night I stripped and cleaned a floor to receive stain using a stripper that requires no neutralizing or rinsing. After staining the super-clean floor this morning, I came back to neutralize and clean in the afternoon, and in the process of neutralizing, washed away almost all color. I applied almost twice the required amount of stain. Is it possible to apply too much stain? Also, I'm told there was an accelerator in the concrete. Could this have caused a reaction? I'm not sure now whether to apply more acid stain, try an acrylic product, or overlay the floor and start over.

Answer:
The first, and most important, comment: Prepare a sample in the future! Applying a small test sample of stain to the floor would have allowed you to see all the above-mentioned problems before you spent the time, money, and headaches on doing the entire floor. OK, off my soapbox now.

From your description, two things jump out at me. First, did the stripping procedure really remove everything you were trying to get off? No matter what the directions say on the stripper, I would recommend a soap-and-water wash after stripping and before staining. Most stripper manufacturers do not take into account that the floor will be chemically stained after stripping.

Second, since you say that you applied nearly twice the amount of stain required, overapplication of the stain is very likely to have contributed to the problem you describe. Stain needs to penetrate to react. If too much stain is applied, the stain solids build up on the surface, creating surface tension. This tension does not allow the stain to penetrate, leaving the stain unreacted on and under the surface. The unreacted stain dries and washes away during the neutralizing and cleaning process. Less is more when it comes to staining concrete. I have recently worked with some highly skilled staining contractors who strive for a super-thin application rate of 400 to 500 square feet per gallon when staining. They produce some of the most beautiful floors I have ever seen.

As for your next step, I would not give up on acid stain. Pick a small, inconspicuous spot on the floor and clean it with soap and water. Reapply the stain, paying close attention to put it down in a very thin, even layer. Work the stain into the surface, let it react for 5 hours, and then clean and neutralize to see the results.