Vermont and its cold winters can turn foundations into a constant struggle. The most commonly affected is an old friend of Green Mountain homebuilders: the concrete block wall.
In earlier years, when concrete wasn’t as readily available as it is nowadays, contractors used concrete blocks as an inexpensive substitute for “pour in place” reinforced concrete walls to build foundations. Unfortunately, these blocks, also known as cinder blocks are not as strong or structurally stable as their counterpart.
The main issue with block walls is that they lack lateral strength. Concrete blocks stacked on top of each other are strong enough to support almost any large building, but not so good when used as retaining walls. When a lateral force puts pressure against a concrete block wall, the blocks lack the strength to resist it, causing them to bow inward. This is a common problem with homes that have block foundations in their basements. The soil on the outside pushes against the foundation wall, and with no counter-pressure on the inside, the blocks will start to bow and crack.
Your first indication of a problem will be cracks around the joints of the block wall. If you see these warning signs, here a few options to stabilize the wall:
- Wooden Structural Retaining Wall (see the video above) – Putting up a wooden structural stud wall on the inside of the block will stop the bowing. This is a good option for an unfinished space, but it may not be as practical for a finished basement.
- Remove the outside pressure – Excavating the soil outside the block wall will relieve the stress. Sometimes the wall can be pushed back into place, but you will still need an engineered solution specific to the conditions of your site before replacing the soil.
- Replace the block wall completely – You can also remove the block wall and replace it with a poured concrete wall. This is typically the most expensive option, but sometimes a necessary one and a more permanent solution too.
- Parging The Wall – Skim coating the wall with fiberglass-reinforced cement is a cosmetic repair that won’t last. As the block wall keeps bowing, the parg coat will crack.
- Ignoring The Problem – This issue is a ticking time bomb and the longer you wait to repair it, the more costly it may be. If the structure moves over time, we may need to lift and level the building before correcting the failing block wall. This would be significantly more involved and costly than repairing the wall early on.
You may go for many years without ever seeing a problem with your block wall. But Vermont winters show no mercy to foundations, so the key is to keep an eye open for signs of trouble and to act quickly when you see them.
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Thanks for the blog post on supporting a block wall- I learned a lot! As someone who is in the process of finishing my basement, this information is really helpful.
I was intrigued by your suggestion of putting up a wooden structural stud wall on the inside of the block to stop the bowing. I’m not sure how practical this would be for a finished basement, but it’s something to consider for an unfinished space.