No matter what time of year it is, among the top issues I get asked about are cracks in a house’s 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, so 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.
How do you know if it’s serious?
There are different types of cracks — step, vertical, horizontal, along walls and in basement floors. If a dime can fit into the crack, get it checked.
You don’t want to see step cracks in cinder block and brick foundations. A step crack is horizontal and vertical cracking between the cinder blocks or bricks; the crack line can look like steps. These types of cracks allow water to get into the basement. Cracks in the cinder blocks themselves are also serious; if you see them, call a foundation specialist as soon as possible.
Extensive cracks — which get longer and wider — in the concrete slab are also no good, and 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. This process involves drilling holes into the part of the slab that’s lower and then using pressure to pump concrete in and raise the slab up so it’s even.
You cannot mudjack concrete slabs that have voids below them, such as 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 involves re-supporting structure, then underpinning — which is a massive project — will be needed.
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, which is when groundwater or extra water from rain or melted snow presses against the foundation wall from the outside. This pressure is very strong, can cause walls to buckle, and is a leading cause of foundation cracks and water seeping in.
A horizontal crack about three or four feet below grade is typically 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 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.
What’s the solution?
The best foundation repairs happen from the outside.
In serious cases, the ground should be excavated to expose the crack on the outside of the wall. The crack is then filled with hydraulic cement that expands as it dries, creating a seal. A waterproof coating is sprayed on and it cures to a rubbery membrane that is 100% waterproof. A dimpled membrane is fastened over top. This process is not cheap but it’s effective.
If you find any cracks in your foundation, either inside your basement or on your home’s exterior, mark them with tape and check them again after a few months. If they haven’t changed in any way they can usually be filled in with an epoxy injection or expandable foam.
But if they get worse bring in a pro, such as a structural engineer or foundation specialist, to assess the situation and recommend the proper solution.
Source: National Post, 1/10/2015