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Question DetailsAsked on 3/12/2015

Y back basement cement block wall has a verticle crack from the bottom up, safe to just fill the crack?

Older home, no other vertical cracks, just this one, it's a little wider on the bottom and gets smaller as it goes up the wall. Top block just has a hair line crack. We have inside French drains to relieve any water pressure, sump pump rarely needs to run. Is it safe to just fill this crack? The blocks are NOT bulging.

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1 Answer


Your description is of a crack (I am presuming not over maybe 1/4" wide) typical for a foundation wall settling a bit due to poor compaction under the foundation, or in soil that was dry when built but now gets wet - the centers of walls settle more than the perimeters as a rule ecause at the corners the adjacent wall helps support it from settling, and the center of the wall is the weakest point in beam action, so it bends downward easier.

If you keep an eye on it and make sure there is no bulging or bowing of the wall, unless it is growing noticeably I would plug it - just a caulk-tube type concrete caulk would work if you have no water issues, otherwise a hydraulic cement like DryLok HydroSeal or Thoro WaterPlug. Then watch to see if it keeps opening up.

BTW - inside french drains do NOT relieve the water pressure (other than maybe under the slab, depending on design) - they just drain away water that has already made it inside your foundation so it does not flood your basement. However, the crack type you are describing is NOT typically indicative of outside pressure issues - that type tends to be wider at the top, and also commonly (but not always) is horizontal, not vertical.

Answered 5 years ago by LCD

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