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I'm fixing up my detached garage built in the early 1900's. At some point there was some movement in the walls (not the slab, the walls are built next to the slab). There doesn't seem to be any more movement; however, there are cracks left between the blocks (none of the blocks themselves are cracked). It seems to be a combination of some decay in the mortar and the settling.

The largest crack seems to be about 3/4" wide and runs from the bottom of the wall zig-zagging up about half way to the corner of the wall.

What would be the best way to fix these cracks? Cleaning them out and adding more mortar?

  • Early 1900's? Really? – Rowland Shaw Feb 21 '15 at 10:25
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Before you patch it, I would recommend making sure it isn't moving any more. One common method is to epoxy a small piece of glass across the crack; if the crack is moving, it will break the glass.

  • Thanks for the suggestion. I'm fairly confident it's no longer moving. Someone told me to put a piece of tape across the crack and if it tore, then it was still moving. The tape hasn't torn yet after a couple months. – john Feb 19 '15 at 5:41
  • @john Tape is pretty flexible. Glass less so. – bib Feb 19 '15 at 12:33
  • Good point, I'll have to try that. How long do I need to wait until I can be sure that the wall is no longer moving? And if it's not, how do I repair it? – john Feb 19 '15 at 13:15
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If you live in a cold climate where the blocks are at risk of cracking from the freeze/thaw cycle, then I would recommend using a caulk that is specifically designed for concrete block.

The color of the caulk will be pretty close to the color of unpainted concrete when it cures, and isn't very noticeable. I repaired a few cracks in my garage with the same product about 3 or 4 years ago, and it seems to have held up pretty well. The caulk remains flexible, and will still stay in place if there is still movement in the wall.

It will take a lot of caulk to fill the cracks. I would suggest buying several tubes at a time. Also, when you install it, you could use painter's tape to leave clean lines. If you look at it from a distance, it should look just like a mortar joint.

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I would fill the cells solid at least one course above the crack then restrike the joints

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