Trying to fix the rehab of '50s formstone


May 14, 1994|By Karol V. Menzie and Randy Johnson

It's an unfortunate fact of life for old houses that when something begins to go wrong -- say, a patch of shingle siding needs replacement -- the owners may choose a short-sighted solution that is even "wrong-er." And subsequent owners are left to deal with the problems.

That's the case for a reader in Baltimore:

"Four years ago we bought a Victorian house (built in 1910) that originally had a brown shingle exterior," she writes. "In the late '50s formstone was applied on top of the shingles to the entire house. Would it be reasonable to remove the formstone for aesthetic and historic purposes? How expensive would this process be? Also, would we lose significant energy benefits from the loss of insulation that the formstone provides? It is safe to assume the shingles will need much repair or replacement.

"A mason once suggested that we stucco over the formstone as that would be a cheaper alternative. . . .TI am concerned that all those layers on the house would cause moisture and insect problems."

The decision to install formstone in the '50s was a bad one. Houses are built to support a particular type of exterior siding, and (usually) designed to look their best only with that type. We strongly believe to preserve and maintain an old house properly, the original surface should be retained. We don't believe in adding layers over the original surface, which adds weight and can indeed lead to moisture and insect problems. Formstone is a particularly bad choice for a frame structure.

Formstone is mortar applied thickly over metal lath nailed through the surface of the building. It was popular in the middle of the century for its alleged "maintenance-free" and "insulation" aspects (neither of which claims is compelling). It was also intended to be applied over masonry, usually brick.

In this case, nailing up the lath and applying the mortar will almost certainly have damaged most of the original shingles beyond repair. Removing the formstone is not a gentle process, either. So, you can expect most of the old shingled surface to need replacement.

It's true that additional layers of siding can provide some insulation value. However, if the walls are well-insulated, a bigger problem with removing outer layers may be air infiltration -- air blowing into the house through gaps, cracks and crevices. Formstone doesn't provide much insulation -- known as R-value -- it merely keeps out the wind.

To answer the reader's question, for aesthetic and historic purposes, the formstone should be removed. However, even if you can do some of this arduous work yourself, the process is likely to be expensive. It wouldn't hurt to get some bids on the work: Consult a masonry cleaner about removing the formstone, as well as general contractors.

If the decision is to remove the formstone and replace the old shingle siding, it's a good opportunity to add insulation and stop air infiltration.

If replacing the shingles is too expensive right now, consider saving up for it. But stucco should never be an option. Stucco is not suitable for a non-masonry surface. It goes up the same way as the formstone -- mortar over nailed-in lath -- and it's equally destructive to the underlying surface. It would be extremely difficult to get a tight seal around doors and windows, and the extra weight could cause all the layers to start pulling away.

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