Request masonry tips – block wall repair
Hello again everyone, I’ve got an old house that has a basement window opening in a masonry block wall that had been boarded up and backfilled. I want to fill the old hole properly with masonry blocks as per the surrounding wall. I’ve never done this, and first of all, I don’t recognize the void pattern and block size. The house is from 1905, but this wall appears to have been added later. The existing wall is 9 1/2″ wide, which is pretty close to the “nominal size” of a 10″ CMU (the 1/8″ difference could just be measuring error since I can’t get my tape on a clean side-to-side space to measure).
1. From the photos attached, does this look like a wall made with 10″ CMU blocks? (I put an 8″ block in a photo for comparison)
2. Should I chisel the old morter off the old window sill before starting again? If so, will chiselling have a negative effect on the surrounding mortar that I want to keep?
Replies
Chisel off old mortar (you won't hurt the existing CMUs. Clean thoroughly. Cut the new blocks lengthwise to fit the hole, leaving room for mortar joints. The last row of block will be somewhat tricky to lay since space is confined. You can set the last row of block on spacers (normally used for tile work. Theses small spacers remain in place. Heck, you can even use wood spacers, as long as you pull them out at some point, and fill in the voids with mortar. Once the last row is laid, you tuck mortar into the joints from inside and outside. I prefer to use a mortar gun powered by a driver. You can do the tuck pointing by hand, but it is harder.
Consider the size (height) of your filler blocks carefully. With proper sizing of the mortar joints you may be able to eliminate a lot of cutting. You could even fill in with bricks, then insulate and frame the inside. Alternately, frame the opening, sheath with water-resistant plywood. Apply a waterproofing agen to the plywood (or sheet good material) and follow up with 1/2" thick cementous tile backer material. I'd thinset the backer to provide uniform and long term adhesion. Just be sure that whatever you do is water proof.
Next, no matter what filler material you use to fill in, you will have to apply some kind of finish material to the fixed area so that it blends well with the exterior CMU wall. I see a waterproofing membrane on one side of the opening. Without more detail it is hard to know how to finish the repaired area.
Mel
Great tips Mel, thanks! I never thought of just filling in the opening with bricks. I may just do that.
Although you will not need many bricks if you are using them, concrete bricks are about half the price of clay. The appearance will be be a better match for any exposed parts.
I would be inclined to set some pins into the bottom of the opening (and possibly elsewhere), given that the mortar joint is likely to crack.