Blotchy and Dark Concrete: Blotchy concrete can result from over application. In order to prevent over application, apply sealers in thin, even coats. If over application does occur, use Xylene to correct the problem.
But if the sealer isn't applied uniformly to begin with, or if not enough coats are used, the slab will appear blotchy upon drying. This is caused by the sealer filling in some of the valleys, but not all, and failing to remain on top of the hills.
When the sealer is applied too heavily, the air displaced through the surface can't escape, and it forms a bubble in the sealer surface. Bubbling of a sealer can also occur if application is done in hot weather, or if the concrete is in direct sun.
Just as with the initial application of outdoor concrete sealers, it is just as important to have the surface resealed. For stamped concrete, the most trusted source suggests resealing every two to three years.
You do not want to apply a second coat after the first coat has dried or the first coat will try to repel the second coat. The second wet-on-wet coat is applied anywhere from 1-15 minutes after the first coat is applied.
Apply the first coat, waiting at least two hours before applying the second. Check your sealant can for specific drying times. Apply two thin coats to ensure a smooth and even finish.
For some reason, this idea that vinegar will remove concrete sealer has become one of the more pervasive myths about concrete, and it is just that: a myth. That's because almost all concrete sealants are made to be resistant to acid, which vinegar is. As if that wasn't enough, vinegar can actually damage concrete.
I asked Bryan if he could give us some insight on what it takes to actually remove a coat of sealer from concrete. He recommends starting with 2,000 psi and stepping it up to no more than 4,500 psi. The temperature of the water varies but is vital in this removal method.
Patching is the simplest and most common way to fix concrete. To patch a surface, you simply apply a new layer of concrete over the old one. This new layer can be textured or smooth, depending on your preference. Patching is ideal for small areas that are damaged or cracked.
It is best to apply two or even three thin coats, allowing each coat to dry between applications. This will prevent puddling that can create uneven coverage. Overlap the areas as you apply the sealer to ensure full coverage.
The removal of old concrete sealer can be done in one of two ways: mechanical or chemical. The mechanical way involves using some kind of tool to physically grind, sand, or blast away the sealer.
You can usually eliminate the humidity trapped beneath the sealer cures by applying acetone solvent on the surface. Start by applying the solvent on a cloth or dipping your brush into it. Then, rub the affected area vigorously with acetone product.
Sometimes it is a patchy sealer
Other causes of a patchy exposed aggregate are the poor application of a sealer or applying the sealer too soon. There are some exceptions; however, sealers should only be applied after the concrete has cured. Concrete needs a minimum of 28 days to cure.
Nutech Re-activating Solvent is used to re-dissolve old concrete sealer prior to re-applying a new coat of sealer. Re-activating Solvent contains a strong blend of solvents, which liquefy old sealers faster and more efficiently than conventional thinners.
Soda blasting, a less aggressive mechanical method, has become more widely used in recent years to remove sealers and coatings successfully. Soda blasting utilizes special high-pressure blasting equipment with commercial-grade baking soda granules as the blasting medium.
The easiest way to remove a concrete sealer is to begin by acid etching the surface of the concrete with muriatic acid. This process can be dangerous if you are unfamiliar with it; however, it is well within the ability of any ordinary homeowner, as long as the proper care is taken.
FastStrip is one of the strongest chemical stripping agents for concrete and is widely used by professional contractors and decorative applicators to prepare a slab with heavy amounts of residual sealers, concrete coatings, and stains to receive a finished surface.
Applying too much product can cause excess sealant to squeeze out and migrate into areas where it might cause trouble – such as clogging the screen of the oil pickup. Try to apply the gasket maker or flange sealant in one continuous and even bead to one surface.
Concrete sealers are best applied in two thin coats. The first coat of sealer acts like a primer. Most of it will disappear into the concrete surface, and the concrete will probably look fairly unattractive after the first coat. The second thin coat will provide an even finish, color enhancement and gloss.
Instead of removing a previous solvent-based acrylic sealer try resealing it! You can apply a solvent-based acrylic sealer directly to the concrete without needing to remove the old sealer. First try and remove any visible peeling and flaking and then reseal according to the instructions.
The answer depends on the surface's square footage. For large surfaces such as commercial floors, a sprayer is faster and way more efficient. Finally, for small surfaces, such as garages or any other exterior surface, a paint roller or any other type of roller will do the trick. Rolling is a less expensive process.
Most concrete sealers dry fairly quickly and usually dry to touch within 1-3 hours. This is true of both penetrating and topical sealers. Penetrating sealers usually fully dry for traffic in less than 24 hours with topical sealers generally taking up to 48 hours to fully dry for traffic.
While it is always best to follow a manufacturer's suggestions for when and how to apply a concrete sealer, we have found the best time to apply most concrete sealers is in the late afternoon or early evening.