Sealing Exterior Decorative Concrete

by Jeff Potvin, The Concrete Network

Exterior decorative concrete has to be protected from elements, chemicals, grease and oil. The surface needs to be slip and stain resistant. Sealers must also have the ability to intensify or magnify the color. While sealers need to meet high expectations, in some cases they are still applied haphazardly. In this article am going to talk about the application and maintenance of a few exterior sealers.

When sealing decorative concrete there are many types of sealers to choose from. Coatings, impregnators and topical sealers are the three major categories. I am going to narrow the field to impregnators and topical sealers. Coatings are not traditionally used on exterior decorative concrete surfaces with their poor breathing ability and UV resistance.

With impregnators and topical sealers it is crucial that the surface is clean when they are applied. When sealing stamped concrete that has a powder release, the release residual must be thoroughly cleaned from the surface. I recommend a solution of 1 part muriatic acid to 10 parts water. This will not only remove the excess release, it will also lightly etch the concrete, removing any laitance for better sealer adhesion and penetration. A common mistake with acid washing is not removing the residual acid, so make sure to flush the surface with lots of water. A pressure washer may also be used to clean the release- this takes a person with a steady hand and a little practice to prevent from removing too much release.

Impregnating Sealers

Impregnating sealers penetrate into the surface of the concrete through capillary action and gravity, sealing the surface from the inside out. Impregnators will not change the surface texture, shine or color. They will only help to prevent staining. So why use them? Impregnators are mainly used in cold weather climates where deicing salt is used and near salt water. Siloxane is one type of impregnator that is used for its ability to screen chloride ions which attack the concrete surface and promote spalling.

Impregnators also reduce the amount of excess moisture intrusion while still allowing the slab to breathe. This decreases the chance of efflorescence or salts on the surface.

Topical Sealers

Ninety-five percent of topical sealers that are used on exterior decorative concrete contain an acrylic resin. They are manufactured in solvent and water based formulas that form a durable thin film. The sealer gives the surface a shine and intensifies the color. Flattening agents are available for those customers who would rather not have the shine.

These acrylic sealers have microscopic holes in the film, which allow the concrete to breath but will still provide stain resistance. The downfall of the solvent-based sealer is its reaction to water. The surface must be totally dry before sealing to prevent pour adhesion or the possibility of the sealer turning white. When excess moisture is on the surface it prevents the sealer from penetrating the pours where the sealer gets its adhesion. If water vapor or excess water enters the film while it is still curing, it will haze or turn white.

The best time to apply these sealers is in the morning just after the dew dries from the surface. Heat can also be a problem while sealing. When ambient temperatures rise above 90 degrees the film may form before the solvents in the sealer have flashed off. The solvent will try to escape raising the film and creating bubbles. This situation will be aggravated when the sealer is applied too thick or allowed to puddle in the low areas such as the grout lines.

These sealers can be applied with a roller, brush or airless sprayer. Make sure when rolling to use a roller cover that has not too long of a nap. I try to use a 1/2" nap whenever possible to prevent bubbles.

Maintaining Sealed Surfaces

Maintaining the sealed surface on decorative concrete will increase its service life. Impregnating sealers need little maintenance other than cleaning. The sealer is below the surface therefore it will not see the same wear as a topical sealer.

Topical sealers need to be reapplied when they become worn. Reapplying a coat of sealer will bring back the sheen and color of the concrete. One problem that can occur from multiple applications is that the surface can become slippery. The film will become too thick losing the texture of the concrete. Using a non-skid additive can resolve this problem.

Sealing exterior decorative concrete is vital to prevent staining and deterioration from the elements. A combination of an impregnating and topical sealer will give you the best protection. The impregnator will protect against salt deterioration and nuisance stains like efflorescence. The topical sealer will protect against staining and will give way to more vibrant colors. You may not find a manufacturer that produces both types of sealers so do your homework to make sure that they are compatible to assure proper adhesion.

Jeff Potvin

Jeff Potvin, a Civil Engineer and the owner of Architectural Concrete Consultants, has nearly fifteen years of experience in the architectural concrete industry. His experience includes stamped concrete, overlays, form-liners, acid stains, counter tops and coatings.

He helps contractors get started in the industry with hands on training, promoting, product selection and troubleshooting. Property owners such as theme parks and retail stores consult with him on product sourcing and maintenance issues. Architects and Engineers utilize Jeff's knowledge on the preparation of specifications and on educational presentations. He is a member of ASCE, ACI, ASCC, IAAPA and the DCC.

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