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Brownstones Require Lots of Maintenance

Written by Al Heavens on Wednesday, 31 July 2002 7:00 pm
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Nothing conjures up visions of Victorian American cities better than streets lined with rows of three-story brownstones and sets of grand steps. It is a material that hasn’t had much press over the last 80 or so years because it hasn’t been in widespread use for buildings at least that long.

Still, restored brownstone houses, purchased by young professionals, have helped turnaround scores of declining city neighborhoods – the Brooklyn Heights section of Brooklyn, N.Y., in the 1980s is an excellent example.

Helped by such a boom in interest, a quarry in Portland, Conn., is again producing brownstone and in growing quantities.

Brownstone, the common name for a whole range of sandstone, was a popular construction material in post-Civil War America, especially in New York City, and quarries in Pennsylvania, Connecticut, New York and Massachusetts provided just about all of the material.

Tastes changed at the end of the 19th century, and brownstone pretty much fell by the wayside - which wasn't surprising, considering that the material didn't quite hold up to the test of time.

As a building material, brownstone has tremendous problems. For example, a church in Brooklyn, N.Y., was built of brownstone in the 1840s. Forty years later, the bell tower had to be removed because it was rotting just like wood.

Brownstone decay is caused primarily by water, and the reasons have to do with the nature of the stone itself.

Sandstone is a sedimentary stone, built up in layers over time, and made of sand and a natural cementing agent.

In nature, the stone is formed on a horizontal plane. When stone is used as a building material, it is “face-bedded,” or set vertically on a structure. Water gets in, shakes the layers loose in a freeze-dry process, and the layers come apart.

Within the stone, natural zones of weakness called bedding planes occur where each layer comes in contact with the next. When water gets in between the layers, they peel away from one another.

In some cases, construction techniques accelerated the rate of decay.

There was a housing boom in the late 19th and early 20th centuries as the population exploded. A lot of this housing, including brownstones, was built as speculative housing, and the work was not, in many instances, top-notch.

Experts say, however, that most of the problems with brownstone are the result of poor or no maintenance.

Some of it has to do with mortar that was used to re-point the stones. The mortar was too hard and would not give when the stone expanded. This causes the face at the joints to crack and break away.

To determine the kind of mortar, a qualified repair person will make a cut down the center of the hard mortar in a joint. The mortar is chiseled out to expose the material behind it, which is then analyzed.

A softer compound, which will be more elastic when the stone expands, is used. The New York Landmarks Conservancy recommends, by volume, one part white Portland cement, three parts sand and lime, and six parts sand and aggregate.

Cracks and broken brownstone have been repaired since the beginning, but the materials and techniques used were kept secret.

Instead of man-made Portland cement, old-timers used a natural cement, mined like gypsum, that was more expensive than Portland cement but worked well. If the cracks in the stone were one or two inches deep, the patch had to be layered in, a half-inch at a time, with a wait of about four hours between each coat.

If there was too much cement, the stone worked against the patch and knocked it out. And sometimes, the stonemason opened up the crack in the stone to repair it, making the situation worse.

Re-pointing any stonework can be expensive, and is best left to expert masons. Prevention is less costly, so here are some maintenance tips: Make sure the joints along the roof line are properly pointed.

Repair roof leaks to eliminate damage. Remove vegetation from and adjacent to the walls. It prevents walls from drying out.

Do not sandblast the walls or clean them with harsh chemicals. Waterproofing chemicals and paint can trap moisture that can destroy the stone. If the brownstone needs to be cleaned, a professional should do it.

Caulk horizontal wash joints in projections such as window lintels or parapet walls.

Do not use deicers to melt snow and ice on brownstone steps.

Do not paint brownstone; it may trap moisture behind it.

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