SUMMARY
This article explains the “black stuff”, also known by its trade name, Flintkote, underneath sidings found on houses built around 1950-1970s
INFO
I have done a lot of housework myself so far so when I rebuilt my entire kitchen (exterior) wall, I was perplexed to find tar-paperish black backboard stuff instead of the usual plywood exterior sheathing.
It was about 1/2″ thick and it resembled more a sheetrock than a plywood. In addition, these Flintkote boards were were attached to the house with nothing more than 1.5″ roofing nails and they could actually be cut with a knife!
What I ultimately found out is that Flintkote is an old tar impregnated homosote (compressed fiberboard) with the outside skin being tar paper.
Flintkote provides superior insulation than that of plywood sheathing, but plywood provides superior structural support.
Flintkote is no longer available so when you get a chance, I would recommend replacing it with 1/2″ or 3/4″ plywood.
Rich
Monday 14th of January 2019
Hi Kevin, last week I had an old enclosed porch re-sided. When the old wood siding g was removed we noticed that all of the walls were covered with the Flintkote that you describe in the article. The installers said that it probably contained asbestos. Any ideas?
kevin
Friday 18th of January 2019
Hey Rich-
Apparently Flintkote used asbestos in lot of their products. Fortunately, I was only able to find references to their roofing and (exterior) siding materials so I don't worry about it.
There were so many products that had asbestos in the 60's, I would go bonkers with anxiety if I had to worry about everything (my house was built in 1966).
Kevin