Have you ever made a repair to concrete such as your driveway, only to have it break off or peel away almost as soon as the job was finished?
You’re not alone. Concrete repair is simple, almost as easy as playing with mud, but four critical steps can make – or break – your repair.
Mess up on any of them, and you’ll probably find yourself repairing your repair or hiring a pro at these prices.
What are these steps?
–First, you have to clean and prepare the old surface to take the repair.
–Second, you should use some sort of a bonding agent to assure good adhesion between the old and the new.
–Third, you must use the right kind of repair material.
–And fourth, you may have to reinforce the repair.
Let’s look at each step in more detail.
Before you can expect any repair to stick, you need a sound surface to bond it to. Chip away any loose, scaling concrete, using a cold chisel and hammer.
While you are chipping, try to shape the edges of the damaged area so the repair can lock into them.
For example, if you want to patch a hole in a slab, undercut the edges of the hole.
After chipping, sweep away all loose dust and dirt. Then dampen the surface with clean water. Dry concrete can suck all the moisture out of your patch and if that happens, strength will drop dramatically.
There are two bonding techniques to help assure good adhesion between the old concrete and your patch. If you are adding a fairly large patch, the cheapest bonding agent is ordinary cement.
Make sure it’s pure cement, not a concrete or mortar mix (both of which contain sand and other ingredients). Mix up a creamy slurry of cement and water, and brush this onto the edges of the repair area just before patching.
Your other option is to use a chemical bonding agent, available at just about any hardware or building supply outlet. This stuff usually comes in cans, and looks a lot like white glue.
You brush it onto the edges of your repair area before you put on the patch. If you are resurfacing (applying a new surface layer to a slab) or applying a thin patch that will feather out at the edges, this stuff is a better choice than the cement slurry.
If you are applying a large, thick patch, you can use ordinary concrete mix. But don’t try this stuff for small patches, for filling cracks, for resurfacing less than an inch thick, or for a repair that feathers out to nothing at the edges. Concrete mix fails in these situations for two reasons:
1. It contains gravel so it won’t work into tight spots or thin sections.
2. In small repairs, concrete will dry out before it has a chance to set, and this will rob it of nearly all its strength.
For jobs like these you should use special patching materials that contain epoxy or latex.
These patching materials stick better, and trowel out thinner than concrete. They also set faster, before they have a chance to dry out, so they are stronger than concrete, at least for small, thin repairs.
You can buy concrete patching material at hardware and building supply outlets, in small plastic tubs or in sacks.
Some types are intended for patching, some for resurfacing, and some will do both. Read the label carefully to get the type you need for the type of repair you want to tackle.
Repairs at the edges, and especially the corners of slabs, are usually subject to severe stresses that can break them off, no matter how well they are made.
For this reason, repairs of this type will benefit from some kind of reinforcement.
One simple way to reinforce such repairs is by using lag bolts or L-screws set into holes drilled in the edge of the repair area. Use a carbide-tipped bit and your electric drill to bore these holes.
Make them a loose fit for your bolts, and about 1 1/2 inches deep. Anchor your bolts in these holes with some patching cement, and then pour the repair right around them, using a simple form.