Although concrete is a very strong and inexpensive building material, it is often prone to cracking. Most problems arise from exposure to the elements. The constant cycle of freezing and thawing may cause cracks and spalling. Another common cause of concrete problems is from uneven settlement of the soil beneath the concrete.
This article will focus on repairing small and midsize cracks in concrete. If you have a very large section of concrete that has been damaged, you really should consider destroying and replacing the entire section. Also, if the cracks you're getting the concrete are from tree roots pushing from underneath, you will need to address the problem of the roots and not just patch the concrete.
To be proactive, and help prevent cracks in the first place, you should consider applying to clear water repellent coating. These coatings help to decrease water absorption and will also reduce the necessity for repairs. Water repellent coatings are available in both water based and solvent based formulas. I prefer the water based formulas personally. They do not last as long, but they are safer and they do less damage to the environment.
To properly repair cracks in concrete, you are going to need a few tools. Some of these tools you may have around the house, others you may have to purchase.
The basic tools you will need are:
· Small sledgehammer (2 lbs.)
· Cold chisel
· Stiff wire brush
· Eye protection
· Whisk broom
· Shop Vac
· Pointing trowel
Materials you will need are:
· Concrete patch mix (powdered type)
· Plastic sheeting (for curing)
The first step in repairing cracking concrete is to clean and prepare the crack for the patching material. In my experience I have found that if you take the time to properly prepare the crack your patching material will last and extremely long time. The method I use to ensure the patching material does not become dislodged is to undercut each side of the crack with a cold chisel and hammer. By doing this you are creating a reverse wedge. It is the same technique that a dentist uses when filling teeth.
Next use your wire brush and whisk broom to clean the crack and sweep out any debris that has fallen down into the crack. If you have a shop vac, use it to help remove debris from the crack as well. Then use your wire brush to thoroughly clean 2 to 3 inches on both sides of the crack. This will help with bonding.
Now it's time to mix up a small amount of your concrete patch mix. I prefer to use a 5 gallon bucket but depending on the size of your project you may wish to choose a different type of mixing container. Using your pointing trowel, scoop (load) a small amount patch mix on one side of the trowel. Next, moving the trowel vertically, tap the loaded side parallel to the crack so that the concrete patch mix slides off the trowel and into the crack. Now use the pointed end of the trowel to force the cement into the undercut areas. After you've forced and as much concrete patches possible use the bottom side of your trowel to finish off the top edge.