Caveats about concrete-raising

MLive.com

Question: I have a section of sidewalk along the side of my house about 40 feet long. About 22 feet of it has settled toward the house foundation. Although I am not getting any moisture in the basement, I would still like to level it so there wouldn't be water standing there after a rain. It also forms ice in the winter.

There is a process called concrete raising whereby they drill 2-inch holes and pump slurry under the concrete, thereby raising the slab to the correct level. I've seen locations where this has been done, and it seems to hold up well. Have you heard of this procedure, and what's your opinion of the method? It's about one-third the cost of taking the old concrete up and pouring new.

Answer: Concrete-raising (or mud-jacking or slab-jacking) is a repair method that has been around for a number of years. It has a proven track record for rescuing concrete that has settled.

The procedure used is as you described. Holes are drilled through the slab's surface, and a grout consisting of sand, water and cement is pumped at high pressure into the area between the concrete and the earth. The slab slowly rises to where it needs to go, the holes are filled and the sidewalk, driveway, or whatever else has been lifted is ready to use immediately.

So, for the purpose you spelled out, concrete-raising would be a good way to deal with the problem of the sloping sidewalk next to your house.

A couple of caveats, though. You said you'd like to ``level'' the sidewalk so water won't stand there after a rain. What you really need is for the concrete to slope away from the house. Leveling it would help some, but in order for the water to run away from the foundation properly, it needs to tip in the opposite direction from where it is now.

Second, you'll need to talk with the concrete-raising company about how much pressure there will be exerted on the top of the foundation wall when the slabs are raised. Certain areas of basement walls are relatively weak, especially at mid-span away from the corners, near an opening for a window or door and at the top of the wall. Many basements, in fact, have inward-bowing walls because of soil pressure alone. Adding to that pressure by injecting a material so near the wall carries with it the possibility of affecting the wall if it is not done properly.

Any concrete-raising company that has been in the business for a while will know how to avoid problems associated with this procedure. And the pressure from the grout injection is relieved by the slab moving upward. But it would still be worth mentioning to the workers so they'll know you're aware of the potential problem.

Sealing the remaining crack between the sidewalk slabs and the foundation wall may or may not be included in the price of doing the raising work. If it isn't, clean the crack thoroughly by scrubbing it with detergent and water, then rinse it well and let it dry. Then stuff it with the lightweight foam material called caulk-backer rod. Backer rod comes in various diameters to fit narrow or wide cracks. Finally, fill up the remainder of the gap with polyurethane caulk to seal out any water that splashes onto the crack. Polyurethane has good flexibility and durability for this purpose; it should last for years.

Zolton Cohen is a Kalamazoo-based newspaper columnist and former American Society of Home Inspectors-certified home inspector. Write to Zolton B. Cohen, Around the House, P.O. Box 2007, Kalamazoo, MI 49003, or contact him online via www.mlive.com/forums/homeimprovement.