Patching Concrete

DEAR TIM: I have tried to patch several areas of my concrete steps, driveway, and sidewalk with little success. Usually, after one year or so, the patch material either crumbles, or completely detaches from the concrete. The weather is always excellent when I patch: sunny, breezy, and hot. Help! What can I do to make the patches stick to the concrete? S.H.

DEAR S. H.: The first thing you need to do is reorganize your schedule. Sunny, breezy, hot days are great for the beach. They are not so great for patching concrete. Sweater weather (50 - 60 degrees F) is a good time for patching concrete.

Your patching attempts failed for any number of reasons. Many of the reasons involve water. High temperatures, sunlight, and wind can rapidly remove water from concrete patching compounds. What's more, the concrete you were trying to patch was probably very dry. In all likelihood, it absorbed water from the patching compound much like a sponge.

This is concrete made to look like brick. Believe it or not, this would be an easy surface to patch. The pattern of the brick is much easier to mimic than a perfectly smooth regular concrete slab.

The water, you added to the dry patching compound, is needed for two reasons. It makes the mix workable. It also is a chemical ingredient. A certain amount of water must be retained within the patching compound for it to become strong. When mixing, water must be added to the dry patching compound with respect. Add too much water and the mix will be weak. Add too little water and the mix might not bond well to the old concrete.

There are numerous things you can do to increase your chances of success. Some of them involve work practices. Others involve your choice of patching materials. Let's start with the different types of patching materials.

Consider purchasing patching materials that contain polymer additives or blended cements. Patching materials that contain these things often stick much better to older concrete. If you see the words "acrylic", "vinyl", or "gypsum cement" on the label, chances are you are in good shape. You can also use liquid additives. Some of these additives are mixed with the patching compound, while others are applied to the surface to be patched. 100 percent epoxy patching compounds are also available.

It is important to prepare the area to be patched. Take some time and remove all loose material and dust. Consider chiseling or saw cutting the edges of the area to be patched. If the edges of the patch are just 1/8 inch deep, the thinner patching compounds often have a better chance to stick to your old concrete. Be sure to wear safety goggles to protect your eyes if you choose to do this.

If using a patching compound that requires water, dampen the area to be patched with a little water. This added water will prevent the dry concrete from stealing water from the patching compound. Try to perform your work on cool, overcast days. If you must work in hot weather, after you are satisfied with the finished texture of your patch, cover it with a piece of plastic and shade the patch from the sun. The plastic and shade will slow down the evaporation of water from the patching compound. Keep the plastic on the patch for a minimum of 3 - 4 days, if possible.