When it comes to concrete, there’s one guarantee that any contractor can give: Its going to crack. Concrete cracks and block walls made from concrete blocks will crack too.
The trick is to control where it cracks. This is why you will see grooves in sidewalks every 4 feet or so. It’s why you will see most block walls don’t run blocks continuously for more than about 20 feet without a control joint. These are controlled cracks.
But even with the best planning, the perfect placement of rebar, the perfect amount of water in the mix, we still see cracks where we don’t want them. It’s just a fact of life that we have to deal with.
Often we can just let a crack be. If we try to fix it, the underlying original cause will just cause the repair to crack too. Or the wall will find a new place to crack instead.
If the wall isn’t deflecting, that is, if you can put a straight edge horizontal across the crack and the wall is still aligned, the crack probably isn’t a problem. It can be filled with a flexible sealer and monitored.
Sometimes we find that just a few blocks are cracked. Maybe something struck the wall. Maybe a tree root lifted the wall. If the underlying issue can be corrected, then we can repair the crack and have confidence it won’t re-crack.
Most of the time, if we’re repairing a building wall, we will only need to make cosmetic repairs to one face of the wall. We won’t have to replace whole blocks. We can just “face shell” the cracked blocks on the exterior of the building. That is, we just cut a few inches deep into the wall (which is typically made up of 8” thick CMU), remove the exposed fronts, the “faces,” of the blocks. We then cut faces from new blocks and install them into the hollowed-out section of the wall. At Mesa Masonry LLC we regularly make repairs like this after a plumber has repaired leaky plumbing pipes inside block walls.
To cut out the face shells we use a small grinder such as a Makita, Milwaukee or DeWalt with a 4 1/2 inch diamond blade. We cut as deep as the blade will go, about 2 inches into the wall, along the horizontal and vertical mortar joints all around the block faces to be removed. When making the horizontal cuts in the bed joints we go about 2 inches past the vertical cuts in the head joints. Once the initial cutting is completed, it’s time to get out the Bulldog.
Bulldog? The best little Jack hammer for this kind of delicate face shell removal, in my experience, is a Bosch Bulldog. Starting about 4 inches in from the end of one of the face shells to be removed we run the chipping hammer straight into the block. Once we have broken out a good chunk of the face of one block we angle the hammer nearly parallel to the wall and carefully chip out all of the bad faces. Be careful not to crack any blocks that you intend to leave in place. Be careful not to chip all the way through the wall.
Once the hole is cleared and cleaned up nicely and ready to receive the new faces, we pre-cut all the face shells to the right depth, about the thickness of the block web, and dry fit them to ensure they will lay in flush. If they stick put we do some more cutting and/or chipping until there’s enough clearance for them to fit in correctly.
Next we mix up the mortar. Unless we need a special color of mortar, we just get the pre-blended mortar available at any big box home improvement store. Once the mortar is mixed to a uniform consistency somewhat like perfect mashed potatoes we let it “set” for about 5 minutes and then shake it up, that is, re-mix it. We’re ready to lay blocks.
If you are comfortable spreading mortar and laying blocks, go for it. If this isn’t something that you are comfortable with at all, I suggest using shims. If you’re only laying a few blocks use a grout bag and shims. Any shims will do. Most mortar joints are specified to be 3/8 inch thick. so you might need two shims, stacked, for each end of each block face. Grout bags are available in the masonry sections and the tile sections of the big box stores.
First test put your mortar to make sure it’s wet enough to allow you to squeeze it through the tip of your grout bag. It needs to be mixed very uniformly or the tip will clog due to the sand separating from the rest. Once you have a consistency that you can easily squirt out of your grout bag, set a couple shims where The ends of the block faces you’re about to install will go. Remember, about 3/8 inch. Next, go ahead and squeeze a bed of mortar on top of the first exposed horizontal edges between the shims, but not on the shims. Then carefully place your block cuts. Ensure your head joints, the vertical joints are about 3/8” each as well. Using a torpedo level on top of the new block faces, adjust the shims so the new blocks align with the existing blocks. Once you’re satisfied, squeeze grout into any voids in the bed joint and fill up the new head joints.
Repeat this process, working your way up. Once you have all your new block faces laid and thoroughly grouted, use a masonry joint striker, or any rounded, smooth tool - - even a cheap plastic spoon works good enough for very small jobs - - to compress the mortar into the joints. Fill any new holes you find, brush or cut off the excess mortar and tool the joints one more time. Try to make your joint tooling match the existing tooling.
If you have experience with a trowel, you could just spread the mortar on the bed joints with the trowel, “butter” the head joints of the blocks and lay them in. An experienced mason can make this look nearly effortless from many years of experience.
If all that above sounds like a nightmare to you, I understand! I feel the same way when I install a new router or try to do something out of my experience, like shingling a roof or assembling anything from Ikea.
I’ve been laying blocks and bricks since I started my apprenticeship in Detroit Local 2, IUBAC, way back in 1989. If you would rather just pay a professional to come and handle it, I get it. Give me a call. I can repair your cracked wall as good, often better, than the original. I have flat rate pricing that covers most jobs so there’s no surprises. I answer my phone or reply to missed calls the same day. And I treat your property with the same respect that I treat my own.