Poisonous Plaster?

By: Bill Kibbel , Contributing Writer
In: Old House Construction

Old-house folklore — I hear it everywhere.  Unfortunately, some home owners believe it if they hear it from people that hold themselves out to be professionals.

In a Canadian newspaper, the Toronto Star, a home inspector was interviewed as the sole source for a piece titled “Take a careful look at older homes.”  On the topic of hazardous materials he states:

“In older homes in the plaster they used horse hair to bond the plaster together and horse hair was treated with arsenic.”

If asked, I don’t think he, or anyone else, could cite a credible source that would substantiate that horse hair in plaster was ever treated with arsenic.  I don’t know of any research, study or testing that would indicate any type of poison would have been mixed into plaster on walls of historic buildings.  I haven’t read about any plasterer, remodeling contractor or homeowner ever getting poisoned from old walls.

There is only one time that I’ve ever heard of someone trying to link arsenic and plaster.  A geologist, studying environmental issues with tanneries in the mid-Atlantic, found receipts indicating small quantities of horsehair from one tannery was sold to plasterers. He also found the tannery used lime (not the kind prepared to be suitable for plaster) and arsenic in processing hides. It was then implied that there might be arsenic in plaster. It seems that this was picked up by a periodical, thus creating a perceived link between what was “discovered” and a possible health risk.

There are only two instances, from credible sources, that have indicated arsenic in building products.  I can no longer recall those sources, but one was about arsenic in pigment used in very expensive wallpaper.  Another source indicated some rare instances of trace amounts of arsenic of iron furnace slag ground up and used for aggregate in mortar.

There are some very real health risks, well studied and documented, that old-house owners deal with regularly.  I don’t think being poisoned by our walls has made it on that list.