Last Fall, after trimming back some large shrubs, I found this crack in the corner of our foundation wall. It was a bit of a surprise because inside the basement there is no evidence of a crack. This is a slightly worrisome development.

After work today, I decided to wield a pick and shovel to do a little investigating. This is what I found. The crack extends down about four feet or so. The “damp proofing” tar that coats the outside of the cinderblocks was below grade in this area.

I am concerned because this house was build in 1965. At that time, there was no building code requirement for rebar or durwall in a cinder block foundation. This type of construction is what is known as “hollow core” concrete. It is not the most stable type, and I believe it is no longer practiced in most places. This type of cinder block wall, without reinforecement, is very unstable in earthquake zones.

I believe what has happened is the front of the foundation wall has been pushed in. The likely cause of this is frost heaving. There were no gutters on the front of the house until last year when I put them on. My theory is that all that water in the ground would freeze/thaw cycle and push the foundation wall inward. This caused the crack on the outside of the foundation with no visible evidence of a problem on the inside of the foundation.

I cleaned off the cinder blocks around the crack with a drill and wire wheel. I repointed the cinder blocks and patched up the other cracks with mortar. I have to buy some tar and plastic to re-damp proof the wall below grade level.

I am hopeful that we have solved the part of the problem by putting the gutters on the house and moving all of the run off water away from the foundation. I plan to keep an eye on this, if the crack opens up again it may be time to rent an excavator and dig out the dirt in the front of the house to see what is going on.

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