Was asbestos used in gypsum-core Homasote-brand exterior sheathing?

This article series describes and provides photographs that aid in identifying various insulating board & fiberboard sheathing materials used on building walls and roofs, such as Homasote, Celotex, Insulite, and Masonite insulating board sheathing products.

Asbestos Content in Gypsum-core Homasote exterior sheathing (gypsum board) product from 1940s.

Was there a Homasote product used in the early 1940s on the exterior of houses that looks like sheet rock? How long does this last for?

If it is still on the house, could it contain asbestos and/or contain mold due to lack of sunlight?

Was there "code" at some point that would have forced individuals who were to replace vinyl siding on the house over these boards to replace with proper products after a certain date? Thank you, K.B.C.

Reply: Properties of Homasote® type fiberboard compared with gypsum-based exterior wall & roof sheathing boards

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with sheathing, leaks, and mold or asbestos sources in buildings - the concerns you expressed. That said, here are some things to consider:

Homasote® fiberboard sheathing is a wood fiber product, not a gypsum or plasterboard product. However there were indeed gypsum-based sheathing board products used on buildings both as wall sheathing (under siding and over studs) as well as roof sheathing.

Please see HOMASOTE HISTORY & PRODUCTS to read the ingredients of Homasote® panels: principally recycled newspaper.

Some Gypsum board and plaster board products indeed contain asbestos as does some joint compound

Watch out: Indeed some gypsum--based drywall products did contain asbestos into the 1980's. I have not, however, tested nor seen test results specifically for exterior wall sheathing using that material. I suggest sending a small sample, a square inch would be plenty, to a certified asbestos testing lab - the cost should be $10 - $50. U.S.

Do let me know what you find as the results will be helpful to other readers.

Even when gypsum board or plaster board did not itself contain asbestos, some joint compounds did contain that material right up into the 1980's.

But used as an exterior sheathing, at the buildings I've seen, there was no top coating of joint compound and tape on this type of sheathing board (as there would be on drywall used for interior wall coverings).

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Continue reading at SHEATHING, FIBERBOARD ASBESTOS CONTENT or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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