Concrete Crack Repair Tips
As you might imagine, the prep work before mixing your patching material is the most important part of the job. This is really true of most building and remodeling jobs.
Most repairs on flat surfaces, such as a driveway, patio or sidewalk, consist of filling a depression or hole. The hole usually has tapered sides. These tapered edges can cause real problems for the long term durability of the patch. The patching compounds thin out at these spots and can easily peel or fail leaving an unsightly second area to patch the following month or year.
I have had the best success patching when I alter the sides of these holes. This can be done with either a chisel and a hammer or a saw equipped with a masonry blade. NOTE: Always wear eye protection and/or ear protection when doing this type of work. Small pieces of concrete, dust, metal or masonry blades can cause severe eye injury. Hearing loss is a real threat as well.
The challenge is to remove the taper from the edges of the hole. If you are successful, the finished edges will be 1/8 inch thick or so instead of tapering to a feather edge.
Mixing the Patching Materials
Always follow directions. Most compounds should achieve the consistency of cake icing or a very thick gravy (don't eat these compounds!) Only mix enough compound that you can apply in 15 to 20 minutes.
Applying the Patch
When using water based repair compounds, wet the surface to be patched, if you are not using a bonding agent. If using a bonding agent follow directions carefully.
For deep repairs, consider installing hardened nails in the depression. For extra deep repairs, drill a 1/2 inch diameter hole and pound a 1/2 inch piece of reinforcing steel into the hole. These items will help hold the patch in place. Be sure that these pieces of steel are at least 1/2 inch below the top of the patch.
Use a finishing tool (magnesium or wood float, steel trowel, etc.) to finish your patched area. Finishing is an art and takes practice. You may have to wait a few minutes until the patching compound begins to stiffen to achieve the desired results. Practice in some out of the way spot, if in doubt.
When you are satisfied with the patch, cover it with a piece of plastic. Weight the edges of the plastic so it will not blow away and so air cannot blow underneath the plastic. This is very important!! Keep the plastic in place for three to four days.
Sunny, hot, breezy weather is the worst time to do this type of work! Many people think it is the best time. These conditions cause the patching compound to dry out too fast. Fifty five degree F weather, overcast and damp is a great time to do this work. If you insist on doing it in warm weather, do it in the early morning. Then, shade the repairs so the sun can't hit them.
Don't attempt to repair concrete in freezing weather. The patches will readily freeze and fail. Use common sense.