Q-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. What can I do to make the patches stick to the concrete?
A-The first thing you need to do is reorganize your schedule. Sunny, breezy, hot days are great for the beach, but not so great for patching concrete. Sweater weather (50 to 60 degrees Fahrenheit) is the best time for patching concrete.
Your patching attempts failed for any number of reasons, many involving 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.
The water you add to the dry patching compound has two vital functions: It makes the mix workable and serves as a chemical ingredient. A certain amount of water must be retained within the patching compound for it to become strong. When mixing the compound, the water must be carefully measured. 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 and others with 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. These patching materials often stick much better to older concrete than other types. If you see the words “acrylic,” “vinyl” or “gypsum cement” on the label, chances are it should work fine.
You also can use liquid additives, some of which are mixed with the patching compound, while others are applied to the surface to be patched. One hundred percent epoxy patching compounds also are available.
It is important to properly 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. (Be sure to wear safety goggles to protect your eyes if you choose to do this.) 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.
If you are 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 do the work on cool, overcast days. If you must do it 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 for at least three to four days.
