Historic buildings need special practices for winter snow clearance (don't use salt)

I am on the Eastern Market Community Advisory Committee, which provides citizen input into how Eastern Market, DC's public market, functions. Sometimes its a form of punishment because of having to spar for years and years with indoor vendors about their preference for fostering car trips to and from the market, opposition to closing the street in front of the market on the weekends, etc. That came up too in this month's meeting.

But for all that I spout about the value of historic preservation, I didn't know too much about how sandstone, limestone, and brownstone are particularly susceptible to pernicious effects from the exposure to the salt (sodium chloride) used to melt snow and ice. Bricks can be damaged too.

So I went to the meeting this month and learned something, which was a bonus. The salt gets in these types of stone and fosters spalling, pitting, and other forms of deterioration.

This is a problem for buildings that are flush to sidewalks, which is typical of historic buildings located in central business districts and in other prominent locations, such as Eastern Market.

The New York Landmarks Conservancy has some advice on what to do (Don't Salt Your Steps). The recommendation is to use magnesium chloride instead of sodium chloride. And apparently there are film treatments and a new type of mortar that can be used in repairs, that improve the longevity of these types of stones in the face of over-exposure to salt.

However, in De-icing and snow removal for heritage properties, the Ontario Heritage Trust recommends calcium magnesium acetate as the best alternative.  So when I run out of what we have, which is magnesium chloride which we bought to reduce the impact of salt on vegetation but our front walk is comprised of bluestone, we'll switch.