Concrete sealer is a compound which is used to protect concrete from the elements. Concrete is a porous material, and without sealing, it will freely breathe. It will also suck up water, which can lead to a variety of structural and aesthetic problems. Many home supply stores carry concrete sealers for people working on projects at home, and it is also possible to purchase sealers through contracting suppliers and specialty companies. Concrete should not be left unsealed, except in certain circumstances.

There are two ways in which a concrete sealer can work. Film forming sealers work by creating a barrier in the form of a layer of waterproofing on top of the concrete. As long as the sealer is in good shape, the concrete underneath will stay dry. It is also possible to buy penetrating sealers which soak into the concrete to waterproof it. Some sealers also include a stain which is used to color the concrete, while others are clear.

The primary difference between these types of concrete sealer has to do with the look of the finish. If a glossy or wet-looking finish is desired, film formers should be used. Matte finishes can be accomplished with penetrating sealers. In both cases, the sealer may need to be periodically stripped and reapplied to keep the concrete in good condition. Some signs that concrete sealer needs to be redone include staining, scuffing, and increased moisture.

Using a concrete sealer prevents water from penetrating, reducing the risk of cracks and other types of water damage. Stains are also greatly reduced with the use of a concrete sealer, keeping floors and other concrete installations cleaner. The lack of staining and moisture can discourage the growth of moss, mold, and other plants which might use the concrete as a substrate. Sealed concrete also resists chemicals and corrosion, making it useful for kitchens and scientific laboratories.

In outdoor installations like driveways and paths, some people prefer not to use concrete sealer. The breathing properties of unsealed concrete allow water to percolate through, rather than running off, which preserves rainfall, snowmelt, and other sources of water. Permeable walkways, driveways, patios, and other outdoor installations help to keep water around the home and garden, which can be useful in regions which are prone to droughts. The unsealed concrete, however, will tend to break down more quickly, which can necessitate early replacement.