02/09/2025
I saw a post earlier about a house with crumbling/disintegrating bricks. The term for that is usually "spalling." I didn't have time to type a reply earlier, but wanted to share some info in case it helps anyone else in the future... older bricks crumbling and disintegrating on the faces is almost always caused by repointing with mortar that was harder and less porous than the bricks. Older brick is much softer than newer bricks that have been fired at higher temperatures. As the bricks expand and contract through the seasons due to moisture and temperature variations, the harder mortar doesn't allow the bricks enough room to expand and it causes the bricks to fail internally and crumble.
A pointer/mason that isn't experienced with older brick can easily make this mistake (and in my experience, most commercial pointers aren't all that familiar with older brick... although thankfully I think this knowledge is spreading!). It often only takes a few years before the damage is noticeable, and it's often seen first on bricks lower on the wall (assuming the whole wall was repointed). It happened to my parents' 1859 house back in the early '90s. It's also SUPER common on late 19th to early 20th century buildings in almost every downtown in the Midwest, because they were "repaired" in the mid 20th century by people who didn't know any better.
If caught early enough, the way to fix the problem (or at least keep the damage from getting worse) is to remove the improper mortar (with a hammer and chisel, a grinder, etc.), replace the bricks that have been completely destroyed, and repoint with a softer, old-fashion mortar. If the newer, improper mortar is left in place, the bricks will continue to deteriorate and eventually the only structural part of the wall becomes the mortar itself (ie: it's not going to last long!). You can't really just cover over the problem if you want the house to continue standing in the long term.
Here are some guidelines for mortar mixes for old bricks in case it helps anyone!
Soft mud bricks, in use before the 1860s, were made by hand-packing clay into wood molds, then firing them in wood- or coal-burning kilns. The bricks are soft, with inconsistencies and irregular edges that give them character. Recommended mortar: 1 part lime to 3 parts sand. Cover and wet for 72 hours before use; to speed the curing process, add about ¼ part lime.
Pressed brick was first made in the mid-19th century; clay was pressed into moulds by machine, then fired in hotter kilns. Recommended mortar: 1 part Portland cement, 2 parts lime, 8–9 parts sand
Wire-cut bricks appeared in the late-19th century. Clay is mechanically extruded, then cut into brick shapes by wires. Wire-cut brick may or may not have holes. Recommended mortar: 1 part Portland cement, 1 part lime, 6–7 parts sand.
I "borrowed" this picture from a google image search as an example. Copied and pasted.