There is a wide range of finishes that offer varying degrees of protection to concrete. Each particular finish or sealer has application, performance, maintenance and other characteristics and requirements that differentiate it from other sealers.
Sealers can be separated into two basic groups: penetrating sealers and topical sealers.
One basic consideration when choosing between penetrating and topical sealers is that sealing concrete that is polished or honed with a diamond grit finer than 200 can be a challenge. The surface is too smooth for many film-building (topical) sealers to stick to. When concrete is polished to a gloss, only penetrating sealers, hardeners and wax can be used.
Penetrating Sealers
Penetrating sealers are liquids that are applied to bare concrete, soak in, and then once wiped off and dried, are usually nearly invisible.
They are really chemical treatments. They often don’t affect the appearance of dry, bare concrete. Some leave it looking dry, while a few provide a darker, wet (but not very shiny) look.
Penetrating sealers work either by reacting with the concrete to decrease its porosity and increase the surface density (the hardeners/densifiers) or by increasing the surface tension to cause beading (the repellants).
Densifiers/Hardeners
Densifiers (also called hardeners) are water-based chemicals that react with the cement paste in the concrete. The reaction generates additional cementing agents that physically increase the strength of the surface concrete and fill the micropores to densify and decrease porosity. The cementing agents that are generated during hardening often serve to provide some color enhancement.
Densifiers are often applied before repellants. Densifiers can sometimes be applied more than once.
There are different types of densifiers:
- Sodium silicates (“water glass”)
- Potassium silicates
- Potassium siliconates
- Lithium silicates
- Colloidal silicates
While the chemistry and reactivity of the silicates differ, their end effect on the concrete’s surface is similar: the concrete eventually becomes harder and less porous. What is important to realize is that reactive finishes take time to achieve their properties.
Repellants
Repellants are a concrete treatment that changes the surface tension characteristics of the concrete so that liquids bead up easily (and therefore roll off or are easily wiped off). They create a hydrophobic water-shedding effect when applied to the concrete. They act like Rain-X® All-Season Windshield Washer Fluid, which causes water to bead up on a car windshield.
The three common forms of repellants are:
- Silanes
- Siloxanes
- Fluoropolymers
Silanes and siloxanes are chemically related. Both are silicone-based compounds that penetrate deeply into the concrete but do not change its appearance. No surface film develops so there is no color, shade or sheen change.
Fluoropolymers are another form of repellant that can be either invisible or color enhancing. Color enhancement brings out the depth of color and shading similar to water, and it sometimes provides a soft sheen too. Some color enhancing fluoropolymer sealers provide a physical barrier (like a coating) in addition to the repellant qualities.
Repellants have very good resistance to abrasion (they are physically in the concrete, not on it), heat and UV.
Oil
Saturating concrete counter tops with oil will not seal or protect them. Oil is oil, linseed, tung, walnut, mineral, olive or otherwise. Soaking the counters in some sort of oil would not offer any form of stain protection. They will continue to stain no matter how much oil you soak them in.
Oil does repel water, but many foods that contain oils won’t be repelled by the oil and will then stain the countertop. And acids will still etch the concrete.
In addition, most oils would be considered natural to some extent, but natural oils can increase the microbial growth on the counters and thus be considered unsanitary.
Using Penetrating Sealers
Penetrating sealers were developed to provide some protection to warehouse floors and to help keep architectural concrete clean from airborne dust and debris. They do not block contact with the concrete, but simply inhibit liquids from penetrating into the concrete, thereby making it easier to clean up spills.
Penetrating sealers don’t provide much, if any, protection against long-term exposure to aggressive staining agents (like wine, mustard and oil), nor will they provide much protection against acidic items. In fact, strong acid usually begins to etch the concrete almost immediately. While some hardened concrete can be called stain resistant, this description really only is accurate in the sense that liquids are far less likely to penetrate into the concrete, thereby making cleanup easier. In other words, concrete that can’t be cleaned is called “stained”, and concrete that is easy to clean up is called “stain resistant”.
Penetrating sealers work best for concrete that gets infrequent or brief exposure to water, mild staining agents and non-acidic substances, and where cleanup is likely to happen quickly. Table tops (like end tables or coffee tables), fireplace mantles and hearths are good examples of where penetrating sealers work best. Because they become an integral part of the concrete, they cannot flake or peel off, and they usually don’t need to be reapplied at all, or for many years. Heat will not affect them, nor will exposure to sunlight.
One drawback to penetrating sealers (especially repellants) is that once they are applied, no other sealer except wax can be applied over them with any confidence. There is a good chance that the topical sealer will not stick because of the repellant. Wax is commonly used over penetrating sealers.
Penetrating sealers are often the only choice available when concrete is polished, since very smooth surfaces don’t allow for a good bond with coatings. Generally a densifier is used during polishing and then a repellant is applied after the polishing is completed. The densifier keeps the repellant from soaking into the concrete. If the repellant is also color enhancing, the densifier will keep the surface looking rich and enhanced.
Topical Sealers
Topical sealers (coatings) make up the bulk of the concrete countertop sealers on the market. There is a wide range of types with widely differing chemistries and varying degrees of appearance, performance and longevity.
Wax
The most basic “sealer” is wax. Wax is both a penetrating and film-building sealer, depending on how much is used and how it is applied. Generally, a high-quality floor wax that contains carnauba and bees-wax, or just pure bees-wax, is used. Synthetic microcrystalline is also used. Automotive paste wax should not be used because of the additives it contains.
Wax produces an attractive, low- to high-sheen finish that brings out the best in the concrete’s color and visual texture. Wax will usually darken bare concrete (similar to the way water wets-out or darkens the concrete).
Wax is a very forgiving sealer. It is easy to apply and hard to get wrong. Wax cannot be scratched (unless it is put on heavily), although the concrete itself can get scratched or gouged. Wax is easy to reapply and usually must be applied frequently to remain effective. Consider wax to be a sacrificial protectant that must be replenished to remain effective and attractive.
However attractive and easy wax is, it makes a very poor-performing sealer. Just about anything will leave some kind of mark or will stain waxed concrete if left on long enough, and exposure times must be fairly brief to avoid any kind of staining whatsoever. Hot temperatures (such as hot sauce pans) can cause the wax to soften or even melt and soak into the concrete. Acids like vinegar or lemon juice tend to strip off the wax and can etch the underlying concrete.
Wax applied over other sealers often adds very little extra protection. It essentially serves little purpose other than to provide a psychological boost to the homeowner, unless the underlying sealer is so poor that the wax actually provides more protection than the sealer itself.
Acrylics
Acrylics, either solvent based or water based, are the next most basic and common concrete sealers. Acrylic is a single-component polymer. Solvent based acrylic sealers don’t “cure”, but merely dry out and harden. They are water-clear and UV-resistant. Acrylic sealers are fairly easy to use, commonly available and relatively inexpensive. They were developed for sealing floors and driveways, and offer modest protection. Solvent-based acrylics will darken the concrete, but not as much as water will.
Most water-based acrylics should be avoided if a dark, wet look is desired. They tend not to wet out the concrete, so it will look pale, almost like it does when it is dry.
Acrylics are thin-bodied liquids that are brushed, sprayed or rolled onto the concrete. While they claim to soak into concrete (only in very porous concrete like a driveway), in practice they only sit on the surface of dense, impermeable concrete that is used in most concrete countertops.
Acrylics offer fairly good stain protection but are easily scratched. Scratches often leave the concrete completely bare and unprotected. Acrylic sealers often require frequent reapplication because they tend to scratch and wear off, especially if the surface they were applied to was not properly prepared.
Solvent based acrylic sealers are fairly simple to touch up because the sealer will melt into itself. Water based acrylics will not melt into themselves because the solvent is water, which will not dissolve the acrylic resin. Because solvents will dissolve the acrylic resin, acrylics are not resistant to most solvents like acetone, toluene or xylene.
Acrylics generally provide modest heat resistance but are UV resistant.
Epoxies
There are hundreds of different kinds of epoxies, but the epoxies used for sealing concrete are all generally similar. Epoxy is a two-component system that chemically reacts when mixed. The reaction is irreversible, and the end result is a very durable, very hard surface. They are usually used for sealing floors, and are generally tinted.
Epoxies are expensive, and because they require careful measuring and rapid application, can be a challenge to apply correctly.
There are three basic types of epoxies: solvent based, water based and 100% solids. Epoxy that is 100% solids means there is no solvent or thinner in the epoxy; all of the material that is mixed together reacts and forms the coating.
Epoxies are very tough and can provide very good stain resistance. Epoxies are generally vulnerable to UV exposure, and yellowing and chemical breakdown can occur if a UV inhibitor or pigment is not used. Even then the best marine epoxies (for use on wooden sailboats) start to break down after only a few years exposure. Epoxies are also heat sensitive.
Epoxies are hard and are usually very glossy and build to a noticeably thick film. Because they are hard (for a sealer) they can scratch easily (hardness is relative and not necessarily always beneficial). The appearance of epoxies can be a problem. A thick, plastic-looking coating that scuffs and scratches easily is not usually acceptable to the clientele who want concrete countertops.
Another difficulty with epoxies is that application can be tricky. Many epoxies are very sensitive to moisture and can bubble if applied to even slightly wet concrete. Bonding issues can occur as well, resulting in peeling.
Urethanes
Urethanes are a class of sealers that offer many desirable characteristics. Some urethanes are single part, and others are two part. There are water-based urethanes and solvent-based urethanes too.
Urethanes, in general, are very stain and heat resistant, provide good or excellent UV resistance, are tough and scratch resistant, and are usually very glossy, but there are also matte versions available.
Urethanes are usually very sensitive to the surface they are applied to. Many urethanes must be applied over a primer, which is often epoxy. Because of this, they tend to look plasticky because of the thick glossy film of sealer and primer that builds up. There are versions of urethanes that do not require a primer and can be applied to bare concrete.
Urethanes can be tricky to apply correctly; they must be measured out precisely and mixed thoroughly. The surface they are applied to must be properly prepared. If these conditions are not met the finish will peel or at least perform poorly. Lastly, urethanes are tricky to repair, since they tend not to stick to themselves, and they are fairly expensive.
Polyurea/Polyaspartic
Polyaspartic polyurea sealers are very durable, high build coatings that are fairly new to the decorative concrete industry. Polyaspartic sealers are catalyzed finishes, meaning they are two-part systems similar to epoxy. However, polyaspartic sealers are very different from epoxies, and these differences have attracted much attention because of the performance and versatility they offer.
Polyaspartic sealers come in a variety of forms, from 100% solids that have near-zero VOC (volatile organic compounds) levels, to 60% solids versions that have relatively low VOC levels. As a family, polyaspartic polyureas offer fairly rapid to extremely rapid recoat times, moderate to ultra-short pot life, very dense, high gloss and high build finish that is resistant to a broad range of chemicals, heat, UV exposure and abrasion. Polyaspartic finishes offer greater abrasion and impact resistance than epoxies and even urethane finishes.
Some forms of polyureas are designed to be mixed in and applied by a special spray gun; these forms cure in a matter of seconds. Newer versions can have pot lives of around 20 to 30 minutes, with recoat times as fast as 1 to 2 hours and walk-on times just as fast. Application is usually by spraying, but rolling or brushing is possible with the longer pot-life forms.
Because most polyaspartic coatings were designed for floors that see harsh use, most manufacturers recommend film thicknesses ranging from 6 to 25 mils (150 µm to 650 µm), or more. For countertops, slightly thinner films can be put down. Because of their ability to wet out the surface, polyaspartics are considered color enhancing, and as a benefit, offer very high bond strengths to properly prepared concrete.
Polyaspartics can tolerate a wide temperature range, and can be applied in conditions ranging from –30 degrees F to as high as 140 degrees F (-34°C to 60°C). High humidity levels usually are not a problem with most polyaspartics, but the higher levels will accelerate the curing rate, but is not usually a problem. However the concrete cannot be damp or wet, because moisture will inhibit a good bond and can flash cure the sealer at the concrete interface, further compromising the bond.
Because polyaspartic finishes offer an attractive assortment of benefits ranging from deep color enhancement, good stain, acid and excellent abrasion resistance, it is tempting to call them the ideal sealer for concrete countertops. However, they are a coating, and as with all coatings they are vulnerable to cuts and scratches. And since the concrete is completely coated, it is never exposed to the environment. This is how the concrete gets its protection, but some countertop manufacturers object to the tactile and visual quality of a glossy sealer. The finish’s thickness and gloss level create an artificially plasticky look that can detract from the overall look and feel that bare concrete offers. And with few reliable exceptions, polyaspartic sealers only come in medium to high gloss.
Reactive Hybrid
Reactive hybrids are a new class of sealers derived from lithium silicate densifiers. These hybrids are a lithium silicate and a proprietary polymer blend. Not only is the chemistry a hybrid, the sealer is a hybrid combination of a penetrating finish and a coating.
Reactive hybrid sealers were originally formulated for concrete floors, and many very similar lithium hybrid products for floors are on the market. There is one company that has modified the basic hybrid product for use on concrete countertops. These products, especially the modified version are new and continually changing to meet the special demands of the concrete countertop industry.
Reactive hybrid sealers are reactive in nature. This means that the sealer chemically reacts with the concrete, so both the sealer and the concrete are altered. The sealer uses calcium compounds in the concrete to initiate curing. This also means that time is an important factor in the physical properties of the sealer. Development of sealer properties is highly dependent on the age, degree of cure and quality of the concrete, as well as the method of application. Part of the ongoing challenge with this particular finish is that there are a wide range of factors that have varying degrees of influence upon the sealer’s performance and curing rate.
Because of its time dependent nature, early age performance can vary widely, but is generally considered fair to poor. As the finish reacts over time, the performance generally increases. This can take days, weeks or even months depending upon a variety of factors such as the degree of concrete curing, the particular version of lithium silicate hybrid being used, temperature, humidity and other factors.
The performance of this sealer is also highly dependent on the particular mix design used, so it is extremely important to test it thoroughly on your own concrete and at various ages of your own concrete. Even then, performance has been highly variable and unpredictable.
This finish is often used in conjunction with a lithium silicate densifier, and is usually applied in the “flood-on, let soak, wipe-off” method. The cured finish is extremely thin, and depending upon the smoothness of the concrete the finish can have a semi-gloss to glossy sheen.
Summary of Penetrating and Topical Sealer Properties
| Type | Stain Resistant |
Heat Resistant |
Scratch Resistant |
Sheen Comments | UV Stable | Easy to Apply | Easy to Maintain or Repair | Other Comments |
| Penetrating
Densifiers: Sodium, potassium, lithium silicates potassium siliconates colloidal silicates Repellants: silanes siloxanes fluoropolymers |
N
(Generally no, but some stain-resistant systems involving lithium silicates are in development) |
Y | Y | Sheen and color enhancement vary | Y | Depends on exact chemical and manufacturer | Y | Once repellants are applied, no other sealer except wax can be applied over. |
| Wax | N | N | N | Natural medium to high sheen | Y | Y | Y | Has to be reapplied frequently. |
| Acrylic
Solvent-based Water-based |
Slightly | Slightly | N | Solvent-based: wets out
Water-based: dry look |
Y | Y | Solvent-based – Y
Water-based – N |
Easily scratched, needs to be repaired frequently. |
| Epoxy
Solvent-based Water-based 100% solids |
Y | N | N | Glossy, thick, plastic look | N | N | N | Stain-proof, but, makes concrete look like plastic. |
| Urethane
1-part/2-part Water-based/ Solvent-based |
Y | Y | Y | Usually glossy, but matte versions available. | Y | N | N | Tricky to apply, very dependent on surface preparation.
Often thick, but there are techniques to apply thinly. |
| Polyurea/Poly Aspartic
2-part Solvent-based |
Y | Y | Y | Usually glossy, but matte versions available. | Y | N | N | Can be tricky to apply evenly; work time could be short.
Often thick, but there are techniques to apply thinly. |
| Lithium Silicate Hybrid
1-part, Water-based |
Slight to Y | Y | Y | Natural medium to high sheen.
|
Y | N | N | Reactive finish; requires time to develop properties; dependent on mix design of concrete and age of concrete |
Summary of Sealing Materials
There is no bad sealer for concrete countertops. There are only incorrect expectations. Regardless of what type of sealer you choose to use, you must set clients’ expectations, right from the start.
The accuracy and completeness of manufacturers’ instructions for concrete sealers vary widely. Even if the manufacturer gives you detailed instructions, test those instructions on your own concrete. Practice with the sealer to make sure you can apply it confidently and consistently.
Test the manufacturer’s performance claims. Use the results of your tests to write detailed instructions for your clients. Here is how to test concrete countertop sealers for stain resistance.
If you understand the sealer you’re using and help clients understand it, concrete countertops can develop a reputation for being both practical and beautiful.