crack between concrete and top course of foundation block

Originally Posted By: dennis petrone
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i have a poured concrete foundation and and extra course of cinderblock ontop of that. i recently noticed a gap about 1/8" between the poured wall and the block layer. I stuck a wire through and it only goes in about 5 inches. this is only on the back of the house and inside the basement. Outside is ok and so are all other walls. Can anyone tell me what this may be if its just normal shrinkage/settling.


Originally Posted By: mkober
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From the description, it sounds like the blocks are rotating “forward” (about their front, bottom edges), probably the result of increased loading along the front faces. If the blocks aren’t anchored to the c.i.p. wall by sufficient rebar and concrete infill, you’ll want to keep an eye on things to determine if the crack becomes noticeably wider. If it does, you may want to hire an engineer who’s had field evaluation experience to assist in determining the cause and a possible solution.

Michael J. Kober, P.E. and H.I.

"NACHI Member and Proud Of It!"

Originally Posted By: dennis petrone
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i was hoping for a little more information if it is a major structural problem. here are some pictures. Hopefully that will tell more.


Originally Posted By: rmeyers
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Unfortunately, a close up of the crack doesn't tell us much about the causes. It's the surrounding conditions and the potential forces at work that we need to see! (Or better yet, an engineer needs to see!)

I think Michael is on the right track. Added courses of block need to be secured to the cast-in-place wall with properly designed re-bar and in-fill. In addition, long anchor bolts should have been used that were embedded into the c.i.p. wall and extended up through the block cores to properly secure the framing and foundation systems together.

The hinge type rotation of the block may result from several different forces at work. The concrete wall may be moving inward due to exterior pressures on the wall. (Not clear if I'm seeing a vertical crack to the left side of the photo?)

The floor system could be expanding and exerting an outward thrust on the top of the wall (Unlikely). However, the floor system will be a stabilizing outward force attempting to hold the top of the wall in position, hence the potential for basement wall inward bulges.

Has the condition existed through a seasonal cycle to determine if there are thermal or moisture factors that are coming into play as they relate to seasonal changes. (Expansion & contraction of the framing and floor systems or soils, etc.)

How wide is the sill plate in relation to the block width and again, is it anchored to only the block with short anchor bolts? If the floor and wall loading is concentrated to the outside edge of the plate and block, there could be torque forces at work lifting the inside edge of the block off of the top of the poured wall. (Per Michael)

Whatever the scenario, the main problem appears to be the inadequate connection or anchoring of the block course to the top of the c.i.p. wall.

This condition has the potential to develop into a major structural issue if the load factors involved are not identified and properly addressed in a timely manner. There will likely be further opening of the crack which may be accompanied by shifting of the block in relation to the top of the c.i.p. wall.

A structural engineer should be brought in to evaluate the situation and make recommendations as to needed repairs to control the problem. Working now with a creative structural engineer to design a re-enforcing repair may be money well spent toward avoiding major structural repairs in the future.

Just my thoughts! Good Luck!


Russ Meyers

Originally Posted By: dennis petrone
This post was automatically imported from our archived forum.

thanks guys. all the connections as far as rebar etc are ok, meaning the sill plate is achored through the block and the c.i.p. There are no vertical cracks. hopefully its just a bad morter job!!!