No matter what time of year it is one of the top questions I get asked is cracks in the foundation: Is it a problem? Should I be worried? How can they be fixed?

Not all cracks are serious. Sometimes when concrete cures or dries it cracks. That’s why it’s not uncommon for new homes to have some cracks along the foundation or in the floor slab. For that same reason I wouldn’t recommend finishing a basement until it’s gone through at least a couple of freeze-thaw cycles (winter and spring). That way if any cracks do show up or get worse they can be fixed first.

How do you know if it’s serious?

There are different types of cracks—step, vertical, horizontal, along walls and in basement floors. If it can fit a dime get it checked.

You don’t want to see step cracks in cinderblock and brick foundations. A step crack is cracking in between the cinderblocks or bricks, which can look like steps. These types of cracks will allow water to get into the basement. Cracks in the cinderblocks themselves are also serious. If you see them call a foundation specialist as soon as possible.

Extensive cracks in the concrete slab are also no good. What do I mean by extensive? I mean cracks that spread and get wider. In some cases they might even cause parts of the concrete slab to heave, become uneven or collapse.

If that’s the case a foundation specialist might recommend mudjacking. That’s when holes are drilled into the part of the slab that’s lower, and then using pressure concrete is pumped in. This process raises the slab up so that it’s even.

You cannot mudjack concrete slabs that have voids below them, for example a porch with a cold room underneath. The concrete slab must be sitting on the ground. You need the pressure of concrete being pumped in between the slab and the ground to raise it. And mudjacking is only good to raise concrete slabs. If the repair has to do with re-supporting structure then you’re looking at underpinning, which is a massive project.

Horizontal cracks along the foundation wall can also be serious. They can indicate that the structural integrity of the wall has been compromised, either due to freeze-thaw cycles or hydrostatic pressure.

Hydrostatic pressure is when ground water or extra water from rain or melted snow presses against the foundation wall from the outside. This pressure is very strong—it can even cause walls to buckle. It’s a leading cause of foundation cracks and water seeping in.

If you have a horizontal crack about 3 or 4 feet below grade there’s a good chance it was caused by freezing and thawing. That’s where the frost line is usually located.

What about vertical cracks?

Vertical cracks, from the top of the wall to the bottom, on two adjacent walls could mean that the foundation’s footing is broken. If that’s the case the footing needs to be repaired, which means excavating all the way down—another big job. But there should be at least two cracks. If there’s only one vertical crack then it could be the result of concrete shrinkage as the wall cured.

Solution

The best foundation repairs happen from the outside.

If it’s a serious crack the wall should be excavated, exposing the crack on the outside. It gets filled with hydraulic cement that expands as it dries, sealing the crack. A waterproof coating is sprayed on, which cures to a rubbery membrane that is 100 percent waterproof, and then dimpled membrane is fastened over top. This process is not cheap but it does the job.

If you find any cracks in your foundation, either inside your basement or on your home’s exterior, mark them with tape. Check them again after a few months. If they haven’t changed, spread or grown they can usually be filled in with an epoxy injection or expandable foam.

But if they get worse bring in a pro, like a structural engineer or foundation specialist. They can assess the situation and give the proper solution. Some fixes will be simpler than others, but no crack should go ignored.