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A Stand-in for Brownstone

Cast concrete can bring damaged brownstone back to life

<p><em>This Old House</em> TV's Charlestown house project</p>

This Old House TV's Charlestown house project

Early on in the project, architectural conservator Andrea Gilmore, who

usually advises This Old House on historic paint schemes, dropped

by the Charlestown house to assess the state of the building's

brownstone lintels and sills. She told us that they were originally

unpainted, and the wood of the bay window was covered in a brown sand

paint meant to imitate brownstone, the effect being one of a unified

masonry building of brick and brownstone.

Climbing and probing, what Andrea uncovered is not particularly

encouraging. Brownstone, a soft sandstone, is prone to erosion and,

since it is a sedimentary rock laid down in horizontal layers, splitting

along its "bedding" lines. Our beautifully carved lintels were worked

parallel to these layers and put up on the building with the bedding

lines vertical, just the ticket for water to enter, freeze, thaw and

split them apart. Past attempts to patch them with some kind of

concrete, and the application of paint, have done little to prevent

their further decay. A few are in good shape, either because they are

out of the rain, like the one beneath the bay window, or perhaps because

their stone is denser. But the rest need help—or, more precisely,

replacing. Not only are they losing their beauty, but the possibility

of pieces spalling off and falling to the sidewalk presents a real

hazard to passersby.

Andrea suggested two possible solutions, each predicated on removing the

decaying lintels. One: Call the Connecticut quarry that still produces

brownstone, get some and find someone to carve them to match the

existing. Expensive. Two: Choose the best of the existing lintels and

make a latex mold of it, fill mold with cementatious mix, repeat, and

paint resulting cast stone lintels to look like brownstone. Less

expensive, but not cheap by any means.

The Charlestown homeowners considered replacing the damaged brownstone, but that

would involve using available or quarried stone that might or might not

match the rest of the house and would require expensive carving.

Pre-cast concrete offered a faster way to repair their home without

breaking the bank. For the decorative and structural brownstone pieces,

we used a rubber relief to create a mold of the damaged brownstone.

Once we have a good mold, we work to accurately match the stone's

color. Then it's time to cast the piece, achieving a good match with

the original. The final product looks great, and helps restore an old

house to its original splendor.