Sealing concrete is a popular do-it-yourself home improvement activity, and it's easy to see why. There's no better, more affordable way to prevent deterioration or add some color or sheen than with a coat of sealer. Plus, contrary to popular belief it isn't terribly difficult and doesn't require any specialized training. Any able-bodied homeowner can seal concrete—all you need is a little patience, practice, and some helpful advice.
A successful sealing job starts with properly preparing the surface you're going to seal. That means you must fill all cracks, make sure the surface is clean and free of mold, efflorescence and debris. If the surface is smooth and you are applying a coating you may need to acid etch or mechanically scarify the concrete. Oil and grease stains can be removed with degreasers. It is also essential that concrete be as dry as possible before application. This isn't the fun part of sealing, but it is the most important part.
Concrete sealers and coatings can be applied with airless sprayers, garden variety pump-up sprayers, nap paint rollers and brushes.
Airless sprayers are usually the best way to apply any sealer. They permit very controlled application rates, allowing large areas to be sealed in the shortest time. They will also handle both water-and solvent-based sealers, high and low solids contents, and any type of resin. The downside is the cost, since they can be expensive.
Pump-up sprayers are cost-effective and best for applying water-based or solvent-based sealers. If using a solvent-based sealer make sure the sprayer is rated for solvents.
Paint rollers with a 1/4- to 3/8-inch nap can be used to apply both water-and solvent-based sealers and coatings. Keep in mind rough surfaces and high temperatures can also present problems when rolling solvent-based sealers due to puddling and surface bubbling. Consider spraying followed by back rolling when sealing stamped or textured surfaces with a solvent-based sealer.
Don’t cheap out on rollers and brushes. And make sure to de-shed your roller prior to application. You can do this by wrapping masking tape around the roller and peeling it off to get rid of loose bits of fuzz. Also run your hands up and down the covers to pull off any remaining loose fibers. High quality rollers and brushes make the job go quick and prevent shedding.
Two serious problems are underapplication and overapplication of the sealer. Underapplication usually happens because the person applying the sealer is either not paying close attention or they are trying to save on cost by spreading it too thin. To avoid underapplying, determine the square footage of the workspace and then follow the directions on the container. Fixing this problem is relatively simple — apply another coat of sealer. Overapplying is more common and more problematic. Overapplication can lead to bubbling from outgassing or create a milky fog on the concrete. It can result in peeling or slow the drying process.
More is not more when it comes to concrete sealers; thin is in. By applying a concrete sealer in thin coats you are preventing any overapplication issues such as tackiness and bubbling. If the sealer calls for two coats wet-on-wet, this means you want to apply the second coat before the first coat dries, or while the first coat is still wet. It is okay to walk on the first coat to apply the second coat. When it comes to concrete coatings one coat is usually sufficient; however, if you are going to applying two coats, or applying a primer followed by a top coat you are going to want the first coat to complete cure before applying a second coat. If a penetrating primer is used such as a densifier or bonding agent, it is best to apply the primer and wait 5-7 days before applying the top coat. This ensures the primer has fully cured and reacted with the substrate itself.