I have a compressed type top on a half wall in the basement and do now know what it is. Can anyone tell me what material this is.
A picture is worth a thousand words but it sounds like an expansion joint.
I'm not positive about what your asking, but the white sheet material looks like drywall held down with screws. It's most likely there as a fire stop for what ever it is covering.
James
Compressed wood on the sill or topic a concrete pony wall. It looks like it got wet and expanded. Not good for exterior walls
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