Concrete Repair Basics

The Foundation of Concrete Repair

Concrete is not always a tear-out and do-over job. In fact, many of the cracks, surface discolorations and imperfections can be easily repaired. In other words: don’t give up on your concrete just yet!  It may have a new life after all.
There are times, however, when concrete can’t be repaired, and should be replaced. This is when there are widespread, deep cracks (caused by settlement, for example), when the concrete has sunken and when frost heave has damaged the concrete. You can certainly try patching, but it will be a short-lived fix.

When Concrete Can’t Be Repaired
When concrete has widespread, deep cracks (i.e. when the concrete has cracked all the way through to the surface), you will generally need to first prepare the subgrade.
The concrete will first need to be removed. Then the subgrade will need to be removed and replaced (sometimes the subgrade can be used again, depending on the situation). The new subgrade will then need to be compacted before the new concrete can be set.
Sunken concrete typically occurs as the result of a poorly prepared subgrade. Sunken concrete may also result if the concrete was subjected to extreme weight.
If you have experienced sunken concrete, you may want to get the advice of a soil engineer to suggest proper subgrading before concreting again.
Frost heave, which is common in colder climates, occurs when moisture in the ground freezes and forces the concrete upward. Like sunken concrete, you will likely need to subgrade again before laying new concrete.
Once you have determined if your concrete does not have deep, widespread cracks, or has sunken or heaved, you can begin the repair process.

How to Repair Concrete
Concrete that is cracked only on the surface, or concrete that has very thin cracks with no signs of settlement, can usually be quickly and easily repaired.
To repair, begin by chiseling the crack using a hammer and cold chisel. Your goal is to create a backward-angled cut in the concrete.
Clean and sweep any wayward material in the crack by utilizing a portable drill (fitted with a wire wheel attachment), or a wire brush.  Take your time to remove all of the debris before moving on to the next step.
Next, apply a thin layer of bonding adhesive over the area. Applying the bonding adhesive with a paint brush is usually the most effective way to ensure that the adhesive is pushed down into the crack.  Bonding adhesive is very useful, as it keeps the materials utilize for the repair stationary in the crack.
A patching compound that is vinyl reinforced is usually the best material to use when repairing cracks. Simply trowel the compound into the crack, and feather the area with your trowel, creating a surface that is even.
Another repair option is to replace the bonding adhesive with sand (that is poured into the cracked area) and use a sand-mix concrete with a concrete fortifier.