Ask the Architect

Cracks don’t heal themselves


Q. I have a cement brick (concave) garage, probably 100 years old. The rear wall has a crack from the ceiling to the floor. The interior opening is about a quarter-inch wide, while the exterior opening is approximately half an inch, with one open area about 2 inches wide. I can now see from the garage interior to the exterior. I was wondering how to address this problem, since water is now coming through the crack, and it expands every year.

A. This reminds me, at the five-year anniversary of Hurricane Sandy, of the 83-year-old woman who was distraught and asked me to look at a similar problem in her basement walls. When I arrived, she sullenly said, “I know you’re here to examine my crack,” to which I quickly replied, “I will, but I hope your husband won’t mind!” She broke into tearful laughter and thanked me for cheering her up. She said she hadn’t smiled for months following the storm.

Your garage’s crack is more than an age-old problem, it was preventable. Masonry is often thought of as very strong and fortress-like. How could something so heavy and solid split apart? Why would it split right down the middle and bow outward? Nature.

In high school, we had a student science and art fair. I built a model home with a removable roof, complete with furniture, wallpaper, carpets, etc. The teachers couldn’t decide whether architecture is more art or science, and finally put my exhibit in the middle, between both. Architecture combines art and science, and should always be treated that way. Your garage decorative blocks, triangular gable roof and color finish were the art. Sadly, science was overlooked. You could say we know much more than 100 years ago, but that would be false. Otherwise, you might cringe when you cross the Brooklyn Bridge or enter a cathedral or the Statue of Liberty.

The main thing to understand about concrete and masonry is its amazing compressive strength. You can place concrete block in a crushing machine under very high pressure and it will resist being pulverized to a high degree. On the other hand, it takes very little energy to pull the same block apart. Concrete’s resistance to being pulled apart is called its tensile strength. Tension is like the action of stretching a rubber band. Block isn’t elastic, so when they built that garage, they assumed that a big old hunk of masonry would just last and last, no problem, so they had no expansion joints and no tension rods, often referred to as rebar. Today we add metal or plastic lattice horizontally in the wall to resist this expansion. Other than scraping the joint clean, inserting a flexible polyurethane backer rod and using a silicone bead sealant on the interior and exterior, the wall would have to be rebuilt, correctly. The bowing is distortion from temperature expansion, and as water freezes in the open crack, it will continue widening.

© 2017 Monte Leeper. Readers are encouraged to send questions to, with “Herald question” in the subject line, or to Herald Homes, 2 Endo Blvd., Garden City, NY 11530, Attn: Monte Leeper, architect.