BILLS BASEMENT BLOG - Wall shear
Wednesday, June 6th, 2012 by Bill Heady
Wall shear is a subject that has come up quite a bit here at Midwest Basement Systems in the last couple weeks or so. So, I thought I'd say a few words about that today.
I've had some pretty lengthy discussions with a couple customers lately about wall shear and the long term effects on the structural integrity of the foundation wall because of it. One question that has come up is why we don't try to correct wall shear when we are correcting the bow in a wall. The reason we don't try to correct wall shear is that as the wall slides in on the bottom block, the top edge of the block can get damaged due to the friction of the wall sliding on top of it. Remember, that wall has the wieght of the house sitting on it. Start sliding that wall around on itself and look out, thats an awful lot to ask of a concrete block. The damage I'm refering to is most evedent on block pilasters (a column of block built in front of the wall to reinforce it) where wall shear is evedent. We see a lot of pilasters that have broken edges and broken corners at the bottom. This is the damage I'm refering to. That's not to say the damage due to wall shear that you see on the pilaster has much, if any, effect on the ability of the wall to support the house or that the pilaster is the only part of the wall effected by wall shear. That's just where it's the easiest to see what I'm refering to.
Now picture the same damage to that bottom block, only now it's on the outside too. Thats what can happen if you try to push wall shear back out. In effect you are grinding away at the top of the block. This is not a good idea. So when we brace a wall that has a little wall shear (1/4 inch or so) we don't worry too much about it. We have, however, braced some walls that that have slid in 1-2 inches at the bottom and we like to give them a little more attention. And we've seen walls that are slid in far enough that replacement is the only option.
Although it is possible to correct some wall shear, I just don't think the damage you could potentialy do to the wall is worth the risk.