Dear James: We have a concrete driveway and a walkway, and both are crumbling. We have received replacement quotes from contractors. What details are most important to choose one? —Mike S.
Dear Mike: A crumbling concrete sidewalk and driveway can be hazardous to walk on in addition to looking really bad. It doesn’t take much roughness and unevenness to cause someone to fall. Once the concrete starts to crumble, it will continue to get worse, especially in climates with daily winter freeze-thaw cycles.
Your original ones probably were not installed properly, because they should have lasted a very long time. A slight shifting and unevenness are not uncommon, but the crumbling surface indicates it wasn’t cured properly.
Extreme weather conditions without proper attention can cause this.
Having a little background in concrete technology will help you evaluate various contractors and their techniques. The Portland Cement Association is an excellent source for basic information on the types and uses of concrete.
First of all, concrete doesn’t dry like paint on a wall. It’s a chemical reaction within the cement that’s activated when it’s mixed with water. The gravel and sand are added as filler and to give more strength to the concrete mixture.
The type and size of sand and gravel used affect the appearance and surface texture.
The cement functions as glue to hold the gravel and sand together. When water and cement are mixed together, crystals form small interlocking needles, binding everything together. The strength of the cured concrete varies and depends upon the relative amounts of cement, sand, and gravel used.
Your local building codes should specify the minimum strength of concrete used for the driveway and sidewalks. Check the quotation from the contractor to make sure the proper concrete strength mixture is specified.
Although it may cost more for a large work crew, adequate manpower is imperative for a long-lasting concrete job. If a contractor cuts corners to save money with too few workers, the concrete may start to set up before they can get it installed and leveled.
To allow for more working time with fewer workers, the contractor may have to add a little extra water to the surface for more time to get it smooth with a nice finish. Adding extra water can dramatically reduce the strength of the concrete surface. This may be what caused problems with your existing driveway.
The contractor should specify wire mesh and 1/2-inch rebar (steel reinforcing rods) in the concrete. This reinforcement minimizes the number of deep cracks in the concrete. Since concrete shrinks as it cures, crack control grooves should be made so the small cracks form only in these grooves.
It’s best if the concrete cures slowly and the surface doesn’t dry out too fast. The humidity level and temperature in your climate impact this. Even though the concrete feels hard in several hours, it takes weeks for it to reach its full cured strength.
