A couple of weeks ago, we answered a question from a reader with a 1920s home in the flatlands of El Cerrito, Calif. Like virtually all houses of this vintage, it has lath-and-plaster walls. It seems the high water table and the ebb and flow of the San Francisco Bay tides was causing the plaster to crack.
Our reader talked with a drainage contractor who recommend a perimeter drain and a foundation contractor who recommended a new foundation.
We didn’t think a perimeter drain was the right fix because the root of the problem is groundwater that rises and falls rather than a stream of water that needed diversion around the house.
A new foundation, on the other hand, could be a permanent fix, but only if it was engineered so that it was deep enough to rest on stable ground. A soils engineer should weigh in. We presume he would come up with a design with pilings to support the spread footings. Our reader also indicated that cost was an issue. Our guess is that designing and building such a foundation would be cost-prohibitive.
We suggested he replace the lath and plaster with drywall to provide some shear support. Do one room as a test and see if that solves the problem.
We received a couple of comments from other readers about our suggestions.
One, a landscape designer and longtime reader, commented that he didn’t think drywall was such a great idea. He wrote:
"Replacing the lath and plaster with drywall might help some, but we have drywall in our house and we have plenty of cracking, particularly over doorways. That might be a lot of work for only a moderate improvement."
He went on to suggest: "Foundation drainage could help if (your readers) have a place for outlet (or a sump pump might be needed). If they have a basement or crawlspace in which they could add some area drains, that would be the other piece — as the water table rises, it goes back out through the drains to prevent flooding. Or maybe just sump pumps are the answer."
We agree that sump pumps may be worth a try in addition to replacing the lath and plaster with drywall.
But the best idea came in the form of a short and spare comment from a reader who identified himself as "an old nail driver." He suggested: "While all the walls are bare, why not install diagonal strapping to stiffen them?"
Perfect. Diagonal bracing is the way to go. We’re embarrassed to say we just neglected to mention this important extra step before the drywall goes on. Do it, and it will exponentially strengthen the structure.
Use metal bracing formed into an "L" shape. It should be placed in the corners of the room and extend diagonally from the top plate to the bottom plate of the framed wall.
Partially cut into each wall stud, slightly deeper and brace. The proper name for this type of cut is kerf. Insert the brace into the kerf and nail the brace to the studs with 8d nails. Carefully remove any baseboard to allow access to the bottom plate.
Then it’s time to hang the drywall, tape and texture, and reinstall baseboard. Some primer sealer and a coat or two of finish paint complete the job.
We warn you, it’s a good deal of work, and it’s going to be messy, so take it slowly and do one room at a time. When you’re finished, absent any major foundation problems, the cracks will be a thing of the past.