Mortar Matters

Mortar Matters
 

If you own a brick home built around the turn of the century, you’ve probably had to pony up to repoint the old mortar. As painful as that bill is, not repointing when the sun starts shining through the wall could be much more painful. So it is at Congressional Cemetery with our old brick walls and burial vaults. At about 70-year intervals, it’s time to call in the masons with their chisels and trowels. Congressional’s vault restoration program tackles at least one burial tomb every summer.

Most historic brick structures were built using lime-based mortars that have the wonderful quality of “breathing” at more or less the same rate as the old bricks. The mortar bonds with the bricks to hold the structure together. A certain degree of softness in the mortar is desirable to allow the structure to wick moisture out of the bricks and respond uniformly to expansion and contraction caused by weather fluctuations.

But lime-based mortars often succumb to the nitric and sulfuric acids carried in modern rainfall. As the rain dissolves the calcium carbonate, the bonding quality of the mortar disappears and the sand in the mortar simply blows away. The photos illustrate the amount of  mortar loss at the Causten Vault in just five years. To use stronger mortars would eventually destroy the bricks themselves.

That’s the phenomenon we’ve been responding to at HCC. The historic brick burial vaults and brick walls that imbue the cemetery with much of its character are suffering the effects of acid rain. We have restored twelve vaults over the last ten years and will continue as long as funding holds out. With restoration estimates ranging from $25,000 to $85,000 per vault, we thrilled to have such great benefactors on our side.

 

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