What does polymer do in GFRC concrete countertops?

The quick answer is it makes the GFRC (glass fiber reinforced concrete) better. The long answer is more involved and explains what it does and why it is important in concrete countertops.

The polymer used in GFRC plays an important role in the strength, appearance and durability of the concrete. Its primary purpose is to reduce the porosity of the concrete and hold the internal moisture within the concrete. This allows the pieces to be air cured and still achieve a 7-day strength equivalent to the same concrete wet-cured for 7 days. Wet curing under plastic is necessary only for the first day (often overnight). Curing under plastic keeps the concrete moist while the polymer coalesces and forms what amounts to an internal curing membrane. The moisture retention also benefits long-term curing to improve the concrete’s mature strength.

The special polymer also has other benefits. It helps with casting and workability.

The polymer improves workability, aids in pigment suspension, and when sprayed, helps the mist coat cling to the forms. Defoaming agents in the polymer help reduce entrapped air bubbles, reducing pinholes and improving the appearance of the cast surface.

Lastly, polymer improves the concrete after the piece has hardened. After casting, the polymer helps reduce drying shrinkage cracks, improves the ductility, and provides freeze-thaw resistance.

Not all polymers are the same, even though they all are milky-white liquids. GFRC polymer is specially formulated for the demands placed on GFRC products. The largest commercial application of GFRC is exterior building panels and facades, which are exposed to the elements in both desert and far northern climates. Yes, GFRC can be used outside!

The specialized polymer used in GFRC was developed and has been used for over 40 years. It is an acrylic thermoplastic copolymer emulsion that contains defoamers and other additives to improve and preserve the concrete it’s used in. The polymer is UV stable, so it doesn’t degrade in sunlight. And unlike many decorative concrete polymers, it will not re-emulsify when it gets wet. (Most polymers used in decorative concrete function as bonding primers, so re-emulsification is a benefit.)

I recommend Forton VF-774 polymer from Smooth-On (formerly Ball Consulting). For more information about Forton polymer, read this article. You may purchase Forton from the CCI store here.

Forton VF774 GFRC polymer from Ball Consulting

My concrete countertop sealer epiphany

Recently I had an epiphany that I would like to share with the world. It isn’t earth-shattering, it isn’t revolutionary and it’s not even that radical. However I believe that it is important, so I’m taking the time to write this.

For many, many years I have used coatings to protect my concrete countertops. I am a strong and vocal advocate for using a high performance coating to protect concrete from stains and acid, and I’ve invested an extraordinary amount of time and resources testing and reporting the stain performance of a wide variety of sealers. My recent epiphany isn’t really about sealers directly, and it doesn’t contradict my position on them. What it does do is paint a broader and more coherent picture of their place and how we all can be successful with our concrete.

We, the concrete countertop industry, are in a strange and precarious position. Other countertop materials have well-defined and widely accepted identities. Everyone who looks at, buys, wants, uses and works with those materials has an idea of what those materials are, and everyone’s pretty comfortable with the way they are. Those countertop materials are accepted, even coveted some may say, at face value. Concrete isn’t given that freedom of acceptance; it’s not given the same benefit of the doubt. So we, purveyors and crafters of concrete have to dig into our bag of tricks and make compromises in an attempt at satisfying challenging, difficult and sometimes impossible demands.

I’m not going to start a dialog on the virtues of such-and-such sealer, or what fantastic new technology is going to solve all our problems. We all are wise enough to know that right now there’s nothing that satisfies everyone; someday perhaps, but not right now. What I am going to say has to do with responsibility. When I’m done, perhaps it will become the map that helps you find the path you’ve been looking for.

When a client chooses Carrara marble, she does so deliberately. Carrara marble has a very rich heritage that is at the source of its wide appeal. It was prized by the Greeks and Romans and widely used as a sculpting material during the Renaissance; Michelangelo carved the statue of David from a block of Carrara marble. The historic and contemporary value of Carrara marble is unquestionably high. Its luminous beauty and refined texture elevate it to super-premium status where it exemplifies high design and expensive taste.

Carrara marble countertop

Although it is highly valued for its rich heritage and aesthetic qualities, Carrara marble is actually a relatively poor material to make a kitchen countertop out of, in a practical sense. Marble is a soft and porous stone, and Carrara’s light color makes almost any stain stand out. Marble is vulnerable to common acids like vinegar and lemon juice.

Despite those limitations, Carrara marble is still viewed as a desirable and valued material. The natural stone industry and consumers are aware of and accept Carrara marble’s physical limitations, yet little is done to improve or protect the material. It is unheard of to apply a coating to Carrara marble. At best a penetrating repellant or a coat of wax is all that is tolerated.

At the opposite end of the spectrum from Carrara marble is a relatively new and popular countertop material. Engineered quartz is a synthetic composite of quartz aggregate in a durable resin binder. This combination yields an extremely durable countertop surface that often carries 10 to 15 year warranties, and its physical properties convey a nearly stain- and acid-proof surface. Its manufacture provides all the protection, so no sealing and no maintenance are required. These factors, along with the broad range of aesthetic choices offered by the engineered quartz manufacturers make it a popular choice and a strong competitor to granite.

engineered quartz countertop

Not to be outcompeted by a synthetic material, most granite on the market today is resin impregnated. This makes the granite nonporous and greatly increases its stain resistance.

Both of these materials, engineered quartz and resinated granite, provide very durable, virtually maintenance free surfaces that can stand up to most anything a homeowner can spill on it.

So where does concrete fit in? From a custom, high-end material standpoint it’s in league with Carrara marble. No other material can look and do and be what concrete can.

Unfortunately, most of the clients concrete is presented to think it’s just another countertop material, and that almost all home-center grade countertop materials perform similarly, providing nearly maintenance-free stain-proof performance. It’s not surprising that most clients ask for, or even demand that kind of performance.

And that leads me back to where I started. You can, and have always been able to, provide your clients with a surface that will stand up to heat, mustard, vinegar and oil (amongst many other sauces and lotions and liquids). Not only do they want “stain-proof”, they want absolutely zero maintenance. No waxing, no resealing, nothing, because even if they had to do it they wouldn’t. After all, if they can’t even keep the countertops clean, do you think they’d apply a sealer every so often, or even once? Not likely. Such performance is possible, but it comes with a price, and that price is that you must use a coating.

These homeowners want to be absolved of any responsibility for keeping the countertops looking like new. In their mind, that’s what the sealer is for. They want to be slobs and not have to worry. And they can, but to get close to what most clients want requires a very high performance coating. A coating that stands up to everything a homeowner can spill on it, and one that does so every time it’s used and on any kind of concrete it’s used on. This places all of the responsibility on you, the concrete countertop manufacturer.

You bear the burden of choosing a finish that stands up to everything you anticipate the client will do. Choose poorly, and you’ll pay the price with callbacks, lost revenue and even lost business. Choose correctly and you can sleep well, knowing your concrete will look like new for a long time.

So where am I going with all of this? I’m not driving you towards one end solution. What I want you to do is think about your concrete and your clients and your message. Are you selling Carrara marble or are you selling engineered quartz? Neither is wrong, but both require an explicit and very clear understanding of responsibility.

If you choose to sell concrete like Carrara marble, tell your clients that 100% of the responsibility for upkeep and maintenance is on them. If you choose to sell concrete like engineered quartz, then take 100% of the responsibility for engineering its performance so that no care and maintenance are required of the client.

Think about this: Whom do you want to bear the responsibility for keeping your concrete looking like new? You or your client? 

While either choice is acceptable, the end product, the concrete, looks, feels and performs differently. You’re not making the same “stuff” and packaging it two different ways. They are different animals, and are looked at and valued in fundamentally different ways. Both are high value. Both are correct, but both must be matched to the right client. If not, then no one will be happy.

Lastly, a word of caution. I believe most of the headaches, callbacks and problems people have had stem from the fact that the finishes conflicted with the defined roles of responsibility.

If I use a finish that provides a good deal of protection, but it gradually wears off, then that finish requires periodic reapplication. If I select a finish that stands up to some common staining agents but not others, then that finish doesn’t provide the kind of protection the client wants. The line of responsibility is vague and shifts. Using some kind of finish that offers limited protection is worse than using none at all because at some level the client knows I’ve sealed the concrete, so the expectation is that staining won’t happen, or it won’t happen so badly, or that it shouldn’t happen. But it will, so in their mind I’ve let them down, even though I set their expectations up front.

This scenario has played out for many concrete countertop makers over the years.

If I simply wax bare concrete, then the client knows, up front, that just about anything will stain the concrete and that they had better take great care and clean up any spills. If they do that then “bad things” won’t happen. And if they do, it’s obvious where the fault lies.

On the other hand, if I coat the concrete with a high performance, reliable coating, then nothing short of gouging the concrete will damage the finish. The homeowners don’t need to do anything. In fact they don’t even need to keep the countertop clean. All the responsibility is on me.

It’s that gray area in between, with finishes/treatments/coatings/whatever that provide limited protection, or only work some of the time for some of the people, or are too difficult to get to work, or simply don’t work when tested despite what’s written on the bottle or posted on a forum. With these types of finishes the line of responsibility is vague. It shifts. It’s movable, and you can be sure that when bad things happen the client will push the line in the direction most favorable to them. And that means you pay the price.

So, are you selling Carrara marble, engineered quartz, or are you caught in between, in the gray area of frustration, callbacks and lost profits? It’s up to you. Just be clear about where you stand.

Efflorescence part 3: Example of repairing a concrete floor

Consider the following scenario: A new urban condo has acid-stained concrete floors finished with an acrylic sealer. The unit downstairs is unoccupied and unheated. The owner notices efflorescence starting soon after move-in and progressively worsening over several months.

We use the example of a floor because concrete floors are generally more susceptible to efflorescence than concrete countertops, and because this actually happened in my condo building in downtown Raleigh, NC.

Efflorescence is occurring because the moisture in the slab from construction and from acid staining has been locked under the acrylic. Water vapor leaving the slab is drawing soluble salts to the warmer side of the concrete.

Fixing this floor starts with stripping off the sealer and then physically removing the efflorescence. Common means are scrubbing or washing with a dilute acid solution. However, you can’t just mop dilute acid (with a lot of water) all over the place. Doing so would pump more water into the concrete. The best solution is to use an automatic scrubber that washes, scrubs and vacuums in one step. This minimizes the amount of water that penetrates into the concrete.

Then the concrete must be allowed to dry thoroughly before lithium silicate densifiers are applied. Commercial dehumidifiers can speed drying.

The final step to finishing the floor depends upon the floor’s water vapor transmission rate, the aesthetics and the desired level of durability. The simplest solution is either to leave as is or to apply a renewable “wax” to the floor. Unlike acrylics, wax is unlikely to trap efflorescence. If it does, wax can easily be stripped and replaced. This process may not halt 100% of the efflorescence, but it will allow everyday cleaning to remove the slight residue that occurs. In areas such as under a bed that don’t get cleaned regularly, efflorescence may still occur.

For floors that require more protection (like restaurants), first conduct tests to determine the rate of vapor transfer. If the moisture levels are low enough, choose a vapor-pressure-resistant sealer based upon the manufacturer’s recommendations. Impermeable sealers that are able to resist the existing vapor pressure will not develop efflorescence because the water vapor cannot pass through the sealer.

Efflorescence part 2: Secondary efflorescence in concrete countertops and floors

All masonry and concrete materials are susceptible to secondary efflorescence, including concrete countertops. Secondary efflorescence is most often caused by moisture or water vapor migrating through a concrete slab, bringing soluble salts to the surface of the concrete. The amount and character of the deposits vary according to the nature of the soluble materials and the atmospheric conditions.

Concrete contains a variety of soluble mineral salts, both from the cement and from admixtures like calcium chloride, and even from chemicals applied to the concrete after it has hardened. It’s those salts that are the “seeds” of efflorescence. Some types of salts simply get dissolved and precipitated onto the surface, while others react with atmospheric carbon dioxide to form mineral crystals.


Efflorescence on a polished concrete big-box store floor.

While all concrete has some soluble salts in it, not all concrete will effloresce. Efflorescence will occur only if all of the following conditions exist within the concrete:

  • The concrete must have soluble mineral salts within it.
  • There must be moisture to dissolve the soluble salts.
  • Evaporation or hydrostatic pressure must cause the mineral salt solution to move towards the concrete surface.

If any one of these conditions is eliminated, efflorescence will not occur.

Knowing that concrete contains soluble salts and that water and the movement of water through the concrete are the cause for efflorescence, then solving the efflorescence problem really boils down to controlling the movement of moisture into and out of the concrete. How this is handled varies depending upon a variety of factors, such as whether the concrete is new or old, cast on the ground or is an interior application.

Since moisture movement into, through and ultimately out of the concrete is how efflorescence forming salts move to and accumulate on the surface, the first step to controlling efflorescence started with the concrete itself, as discussed earlier in the primary efflorescence section.

Managing moisture is the next step to controlling, minimizing or even eliminating efflorescence. Dry concrete is far less likely to effloresce, so identifying moisture sources and then controlling the movement of that moisture into and out of the concrete becomes the key to shutting efflorescence down.

Consider a basic concrete floor slab cast directly on leveled, compacted ground. The concrete itself contains moisture, and if it’s made properly the concrete won’t generate primary efflorescence due to the bleedwater evaporating and leaving salts behind. But secondary efflorescence can, and probably will, occur. That’s because the ground beneath the slab is a moisture reservoir. If water was added to the sand or gravel to assist compaction, that added moisture will eventually migrate through the slab, carrying mineral salts with it and forming efflorescence. The reason vapor barriers are installed beneath concrete slabs is to isolate the concrete from the ground, which represents a large reservoir of moisture.

If the concrete floor is then sealed with an impermeable coating like a urethane or epoxy, vapor pressure or even hydrostatic pressure can cause blistering or sealer failure. Breathable coatings like acrylics allow water vapor to pass through the sealer, preventing blistering. But migrating water vapor can slowly cause salts to accumulate beneath the acrylic sealer, causing unsightly blushing or even sealer failure due to accumulated mineral deposits.

Commercial floors in elevated structures are not cast against the ground, so there’s no moisture reservoir beneath the floor to drive efflorescence. Yet these floors can effloresce too. That’s because water can enter the slab from the top during the course of finishing, acid staining and routine cleaning. Porous concrete absorbs water during mopping, and copious amounts of rinse water pump large volumes of water into the concrete. This moisture then leaches the salts out of the concrete, creating efflorescence.

Controlling secondary efflorescence is a more common problem for contractors who have “inherited” pre-existing concrete. The mix itself can’t be changed, so factors that affect water movement into and out of the concrete are where steps can be taken. Identifying and minimizing the sources of moisture are the first step. Reducing the porosity of the concrete to prevent the soluble salts from being leached out is the second step.

This second step to controlling efflorescence is to apply chemical hardeners, also known as densifiers, to existing concrete. These make the matrix less porous by generating calcium silicate hydrates that plug the pores and clog the capillaries. Done properly, they offer a threefold benefit. Reduced porosity is the first. The second is that silicate hardeners consume free lime in the concrete. Thirdly, the silicate gel binds other soluble salts, making them difficult to leach out.

While chemical hardeners seem like the ideal solution, not all hardeners are effective. In fact, using the wrong type can actually cause efflorescence. Explaining this involves a little chemistry, so bear with me.

Three common forms of chemical hardeners are sodium silicate, potassium silicate and lithium silicate. Lithium silicate hardeners are the most effective and least likely to effloresce due to a combination of factors. Lithium ions are smaller, and compared to sodium or potassium silicates, there are fewer lithium ions for each silicate molecule. It’s the silicate portion that actually does the work, so in effect lithium silicates are more concentrated. Once the silicate molecule reacts with the available calcium or free lime in the concrete, the sodium and potassium ions are freed and become soluble. In contrast, lithium ions are not freed. Free ions can react with other substances in the concrete to form salts. These salts can then leach out and form efflorescence.

Finally, high concentrations of carbon dioxide (CO2) can cause or accelerate efflorescence. Concrete located in areas with gas, wood or oil-fired heaters will develop efflorescence faster than concrete stored in low CO2 concentrations.

Preventing Efflorescence in concrete countertops and floors: part 1

Efflorescence. It’s the whitish powdery material that forms on the surfaces of masonry or concrete construction, and also it’s the white blush that can form on sealed concrete floors or concrete countertops. While it poses no threat structurally, efflorescence is an aesthetic nuisance that affects both interior and exterior concrete. This article discusses why efflorescence occurs, how it can be prevented and how to deal with it if it does happen.

efflorescence on a concrete wall

Efflorescence “growing” on the inside of a concrete block wall.

There are two kinds of efflorescence: primary and secondary. Primary efflorescence occurs when concrete bleedwater dries on the surface. Secondary efflorescence occurs when soluble mineral salts are leached out of cured concrete. This post will cover Primary Efflorescence.

Primary Efflorescence

Eliminating primary efflorescence begins before the concrete is cast, simply by using basic good concreting practices: Start with a concrete mix that uses well-graded aggregates, a low water-to-cement (w/c) ratio, and fly ash or other pozzolan as a partial cement replacement; use a water reducer to increase workability without adding extra water to the mix.

Extra water in the concrete makes it more porous, weaker, and more susceptible to shrinkage cracking. The extra water is an unwanted internal reservoir that can leach the salts out of the concrete. Concrete made with a w/c of around 0.45 will produce a strong, dense mix that’s unlikely to have excessive bleedwater.

Fly ash adds workability and replaces some of the cement. Since it’s a pozzolan, it consumes the calcium hydroxide produced during cement hydration. Calcium hydroxide, also known as free lime, is a key efflorescence-producing compound. Pozzolans consume the calcium hydroxide and produce calcium silicate hydrates, which make the concrete stronger, denser and less porous. This reduces the likelihood of efflorescence by shrinking capillaries and plugging the pores within the concrete.

Making good concrete is just the first step. It does no good to have a well-designed, low w/c ratio concrete if it’s not cured properly. Wet curing under burlap, plastic sheeting or curing blankets allows the concrete to gain strength and density during the critical early days after casting. In young concrete, the capillary and pore structure is open and well-connected. As the concrete cures, the pores and capillaries get filled in and closed off, yielding a dense, more impermeable matrix. Well-cured concrete inhibits water movement, and this is one important step to controlling primary and secondary efflorescence. If the concrete doesn’t allow moisture movement, the salts deep within the concrete can’t be leached out.

Conversely, concrete that dries out quickly soon after finishing is sponge-like, filled with cracks and interconnected pores that allow moisture to move into and out of the concrete. Rapid evaporation of moisture draws efflorescence-causing salts to the surface through the porous, micro-crack filled, weak concrete matrix. Not only will efflorescence happen, it will continue to happen because the concrete never had a chance to cure into a dense, solid mass.

Next post: Secondary efflorscence

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