Hi Bill, Have to admit that I'm not sure if you are referring to the kool-aid inspector, me, or both. Anyway, I'm always open to new information. I see a lot of lath and plaster homes in Buffalo. I see many non-load-bearing walls covered with the stuff and I have read several articles on how to repair it. I appreciate its texture and its beauty - especially compared to gypsum. But arsenic in horse hair? It's all new to me. Rather than slam someone as incapable of cognitive thought (don't know what other kind there is), I like to be given references with facts. To me, that's what sites like this are for. Although the third plaster layer did not normally include any animal hair, I know that the render layer and floating coats often did. You are likely the one best qualified here to educate others on early building materials and practices. You are normally very helpful and not insulting. Was horse hair not one of the animal hairs used? If horse hair was used, then why was it different from 'other' horse hair that did contain arsenic? I truly don't know - and I think you must. What I gather at this point is that some arsenic might exist in old plaster but the amount is so small as to be insignificant except to those who are unreasonably phobic. I just like to know the facts.