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Sealer: The Most Critical Success Factor for Concrete Countertops

Author and artisan Jeffrey Girard of The Countertop Institute puts sealers under scrutiny with a battery of stain and acid tests.
Author and artisan Jeffrey Girard of The Countertop Institute puts sealers under scrutiny with a battery of stain and acid tests.

Do you know the single-most important ingredient in a concrete countertop that can make or break a business? If you thought concrete, think again — it’s the sealer.

You can make the most beautiful concrete countertop in the world, but in the end it’s the sealer that determines almost all of concrete’s performance characteristics: stain resistance, heat resistance, scratch resistance, food safety, ease of cleaning and maintenance. Short of making sure your concrete doesn’t crack, everything else depends on the sealer.

This concrete sink was sealed with a high-performance water-based urethane sealer. Photo courtesy of The Concrete Countertop Institute
This concrete sink was sealed with a high-performance water-based urethane sealer. Photo courtesy of The Concrete Countertop Institute

Meeting performance challenges
Professionals worldwide are creating amazing products including kitchen and bathroom countertops, sinks, tubs, furniture, fire pits, wall panels and planters. The possibilities are endless. While most of these creative concrete products generally require some kind of protective sealer, kitchen and bath countertops and sinks have by far the most challenging and demanding performance requirements.

Especially in a kitchen, homeowners expect their countertops to be stain-resistant, heat-resistant, scratch-resistant, food safe, easy to clean and easy to maintain. After all, the most popular countertop surfaces, granite and engineered quartz, meet all these criteria. Why shouldn’t concrete?

In the past, concrete countertops got a bad reputation as stain prone and high maintenance because of the wax and acrylic sealers once used. Unfortunately, this reputation persists even today, despite that most concrete countertop professionals are now using high-performance coatings to provide excellent protection to their creations. There is still a lot of confusion among consumers, designers and even concrete countertop pros about sealers, and there are still basic acrylic sealers and penetrating treatments marketed for concrete countertops.

I’m a strong and vocal advocate for using a high-performance coating to protect concrete from stains and acids, and I’ve invested an extraordinary amount of time and resources testing and reporting the stain performance of a wide variety of sealers. I’ve always used coatings, even back in the late 1990s when they required a full-suit respirator, HVLP sprayer and several days to apply properly.

Urethane coatings are easily applied with a roller. Photo courtesy of The Concrete Countertop Institute
Urethane coatings are easily applied with a roller. Photo courtesy of The Concrete Countertop Institute

Since then, technology has advanced dramatically. The popular coatings today are water-based urethanes applied with a foam roller. Many very successful concrete countertop professionals exclusively use urethanes on countertops. They’ve done so for years because their businesses and their reputations depend upon the performance, consistency and dependability urethane coatings provide.

 

Urethane coatings are tough
Coatings work by forming a physical barrier that prevents stains from everything that comes in contact with the concrete. Just as car paint makes a car beautiful, it also keeps it from rusting. In contrast to barrier-forming coatings, penetrating treatments such as reactive densifiers and repellants leave the concrete surface bare and vulnerable to acid etching. Etching is physical damage that can only be polished out, something few customers are capable of.

These concrete sinks by Brent Indenbosch of Diamond Finish Concrete Countertops in Chilliwack, British Columbia, are sealed with urethane. Photo courtesy of Diamond Finish Concrete Countertops
These concrete sinks by Brent Indenbosch of Diamond Finish Concrete Countertops in Chilliwack, British Columbia, are sealed with urethane. Photo courtesy of Diamond Finish Concrete Countertops
Urethanes are coatings that have properties which make them an excellent choice for sealing concrete. Urethanes (especially ones tailored for concrete countertops) are highly chemical-resistant and are inert once cured. They’re very heat- and sunlight-resistant, with the very best showing no yellowing effects of strong UV exposure in exterior applications. And finally, they’re tough. Most wood and vinyl floors have urethane coatings that protect the floor. If those are tough enough for a floor, why can’t urethanes be tough enough for a countertop?
 

In addition, a urethane coating doesn’t depend upon the concrete to develop its properties. The types of urethanes the pros use are catalyzed, meaning there’s a part A and a part B. These two components are what create the protection.

Tim Sprules of Forma Studios in London, England, uses urethane to seal outdoor furnishings. Photo Courtesy of Forma-Studios
Tim Sprules of Forma Studios in London, England, uses urethane to seal outdoor furnishings. Photo Courtesy of Forma-Studios

The underlying concrete has no real impact on the performance of the urethane coating, provided the concrete is not weak, overly porous or full of pinholes, characteristics that professional-grade concrete used in countertops rarely has. In stark contrast, some boutique and esoteric reactive finishes only work with proprietary concrete mixes. Their effectiveness and dependability can unexpectedly vary if they’e used on a different mix.

Still, nothing is perfect
However, coatings are by no means perfect. I’ve written about what the “ideal sealer” is before: It would be easy to apply with little skill or practice, work on any kind of concrete, resist stains and prevent etching damage from acids. It would be scratch-proof, heat-proof and sunlight-proof. It would work fast and be inexpensive.

Unfortunately, no such sealer exists. Today’s water-based urethanes come close. However, they do have two drawbacks.

The first drawback is scratching. Some finishes scratch easily, while others are harder to mar. Generally, the scratch resistance of a finish is tied to its abrasion resistance, a characteristic quantified by the Taber abrasion test. Urethanes have some of the best abrasion resistance of any coating.

Granted, even the best urethane can still scratch. Unless a coating is made of diamonds, it will scratch. There is no way around this. I believe this is far preferable to staining and etching for the following reasons.

No countertop surface should be cut on — ever — except wooden butcher block. Soft surfaces like laminate will scratch, and hard surfaces like granite or quartz will ruin knives. I’ve found that customers would rather not have to worry about staining and etching (and water­marks — that should never be an issue) than have something they can cut on.

Cutting is a deliberate act, whereas spills of lemon juice, red wine and oil are accidental, or unintentionally overlooked and not wiped up. That deliberate act of cutting can be prevented by setting expectations with the clients, and putting in the contract and the care and maintenance guide that they can’t cut on the countertops or it voids the warranty. If you’re really worried about it, give them a wooden cutting board with your logo as a nice gift.

Ensuring the bond
The second drawback is the possibility of adhesion failure. Unlike simple penetrating treatments that get wiped on and soak into whatever they’re applied to, coatings require some surface preparation, often acid etching or light honing. This is to promote adhesion which ensures a strong and permanent bond to the concrete. A coating’s most common failure is peeling, and nearly all adhesion failures are caused by inadequate or incorrect surface preparation.

A very common cause of adhesion failure is the assumption that dry grinding is the same as wet grinding for surface preparation. It’s generally well known that if you’re going to apply a coating sealer, you need to stop at 200 grit. Going further will not only make the concrete too smooth to have any “tooth” for the sealer to bond to, but also it’s unnecessary work because the sealer determines the sheen of the concrete.

However, grinding to 200 grit with dry pads is not the same as grinding to 200 grit with wet pads. The dry polishing process creates concrete cuttings which don’t get flushed away like they do with wet polishing. Because the powdery cuttings tend to remain under the polishing head longer, they break down and act as finer polishing media.

A “200 grit” finish with dry pads is actually like a much finer finish, something like 800 grit. Additionally, the powdery cuttings get forced into the open concrete surface pores, contaminating the surface, and that can cause adhesion failure.

Worth the effort
Those who advocate treatments rather than coatings cite scratching and adhesion failure as reasons to stay away from coatings. As I’ve just explained, these issues are manageable, far more so than installing a kitchen countertop that ends up staining and etching from red wine, olive oil and lemon juice.

High-performance urethane coatings are worth the effort to provide peace of mind. Coating technology has advanced to the point that today’s urethanes are water based, relatively easy to roll on, very scratch resistant and great looking.

So if many large and successful concrete countertop companies choose a urethane coating that keeps their customers happy and coming back, why shouldn’t you?

Jeffrey Girard, P.E., is founder and president of The Concrete Countertop Institute and a pioneer of engineered concrete countertops. He can be reached at info@concretecountertopinstitute.com.

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