How do we repair damage from basement flooding? Our cottage has a fully-insulated basement with a concrete floor. Thanks to a sump well and proper drainage, this basement has stayed warm and dry for years. But in 2019-2020 there were record-high water levels on the Great Lakes. The water table rose to just under our floor. As the water table started to drop, a white powder appeared on the floor, and also around support pillars and internal block walls. What is this white powder, and how do we remove it? Once that is done, is there a product we could use to coat the floor?—Bob and Joan Bowman, Sauble Beach, Ont.
The white powder is likely efflorescence: the visible salts and minerals left behind when water evaporates. It’s not pretty, but it won’t hurt you.
Try cleaning it with vinegar and a scrub brush—that should remove it. If not, you could use a dedicated efflorescence cleaner. (Check hardware or home reno stores.)
As an absolute last resort, you could “upgrade to muriatic acid,” says Roger Frost of Napoleon Home Inspections in Barrie. (But PSA: it’s terrifyingly caustic stuff. The expert advice on using it ranges from “Cover every part of yourself in protection; consider installing an eye-wash station” to “Don’t touch it. Don’t even look at it.” We’d rather live with the white powder.)
After cleaning, you could coat the floor with an epoxy paint, but it can be prone to flaking, peeling, and blistering—that might look uglier than leaving the basement bare. And it’s not going to provide much waterproofing.
“Stopping water from coming in is the best solution, and that could be impossible if the water table rises again,” says Frost.
Still, you have a few choices to handle future dampness problems, says Don Fugler, a building scientist formerly with the Canada Mortgage and Housing Corporation (CMHC): regular cleaning to deal with any stains, a “false floor” to hide the stains, or installing a pump to work with the sump and keep the water several inches lower than the floor. “But be aware that, if you are trying to stem the movement of water from a Great Lake, that pump might be running continuously for weeks,” says Fugler. A more extreme option would be to change the basement into an isolated crawl space, he says. Excessive? Maybe, but cottage country could be in store for decades more of high-water levels and flooding. “Who knows what eventually will happen with a changing climate?”
This article was originally published in the August/September 2021 issue of Cottage Life magazine.
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