Here is a guide to the products needed for typical concrete repairs. The products are sold at many home centres, hardware stores and building-supply dealers.
* Large cracks, potholes, major repairs. Concrete mix, generally sold in 60-pound or 80-pound bags, is the usual choice for these repairs. It is a mixture of Portland cement, sand, and fine gravel. An 80-pound bag usually costs $2.50 to $3. As a rule of thumb, concrete mix should be used for any repair that requires a layer with a thickness of two inches or more. Dry concrete mix is simply mixed with water before use and repairs should be kept damp for several days after application. The bags have full instructions for mixing and using the material. A metal wheelbarrow or large plastic tub are fine containers for mixing; a garden hoe makes a good mixing tool.
* Medium-thickness repairs (less than two inches). An inexpensive product called sand mix is a good choice for repairs if a thickness between 3/8-inch and two inches is required. Resurfacing a damaged area in a sidewalk is an example of proper use of sand mix. Like concrete mix, it is sold in bags and costs about the same. Sand mix does not contain gravel and can be spread in thinner layers than concrete mix. A 60-pound bag of either concrete mix or sand mix makes about 1/2-cubic feet of material, enough to form a two-inch-thick layer covering three square feet.
* Shallow repairs and smaller cracks. Concrete sometimes flakes at the surface, leaving shallow depressions that require special materials to repair. Vinyl patching cement, often sold in small bags or plastic tubs, is a good choice for these repairs because it has excellent adhesion and can be spread in thin layers and tapered at the edges. Vinyl patching cement is also a good choice for repairing cracks less than 1/2-inch wide. This product costs considerably more than concrete mix or sand mix, and should not be considered for major repairs. When vinyl-cement repairs require very fine tapering at the edges, a damp paint brush can be used. When used in narrow but deep cracks, pack the bottom of the crack with sand or plastic rope (sold at home centres) to within about 1/2-inch of the surface.
* Easy small-crack repair. Do-it-yourselfers have several other choices to repair cracks up to about 3/8-inches wide. Patching products for these cracks are sold in liquid (just pour into the crack) and caulk form (apply with a caulking gun). It is vital to read and follow the instructions for these patching products if lasting repairs are expected.
* Cracks between concrete blocks, bricks and stones. Mortar is generally the binder in structures built of these materials, and mortar mix should be used for repairs. The product is usually sold in 60-pound bags and costs about the same as concrete mix.
* Resurfacers. These are designed to literally put a new surface on unsightly concrete. Advertisements for these products often show someone with a squeegee spreading a bright new surface over an ugly driveway or sidewalk. In practice, resurfacing is somewhat more complicated than that. For example, Quikrete Concrete Resurfacer (about $22 for a 40-pound bag), requires that the surface first be cleaned with a power washer capable of generating 3,500 psi (pounds per square inch) of pressure.
Resurfacing also won't work well on surfaces that are deteriorated or cracked. Suitable repairs must be made first.
--Knight Ridder Newspapers
Anyone contemplating a concrete project should consult the Web site of Quikrete (www.quikrete.com)