My house appears to be sheathed in some kind of fiberboard product with a black paper facing on the inside. That rock-looking thing poking through is stucco. The house was built in 1972. Anybody know what exactly this material is? Good or bad? Is it evidence of shoddy, terrible construction? Can this stuff be expected to hold a screw if you wanted to screw something to it? Am I the one who's screwed? ;-)

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3 Answers 3


The material you have there is what I was taught to call celotex. There is a manufacturer that has the same name that may have been the original maker of this product.

It is pretty much the equivalent of loosely packed sawdust drawn into a sheet and held together by binding agents and tar, I believe on the outside surface. Research on ther internet may show it is made up of something else, never the less it is not that strong, and would not work as windbracing on its own. Many, many home have this under their siding.

It will not hold a screw, it is used for sheathing only that I am aware of in all my years. You are not screwed for having it, just like any other sheathing, you don't want it to get exposed to water, especially this stuff.


Back in the late 60's early 70's we used a similar material called BildRite that was applied as sheathing. It was promoted at the time as having better insulating characteristics than plywood or wood boards. It was also significantly lower cost.

The stuff cannot support fasteners. Anyplace from the outside where fasteners must be used there has to be backing nailed into the stud cavity.


Evidence of shoddy construction? As in a construction that would collapse, as if it was built by a typical 1970's DIY homeowner instead of a real tradesman? No, but it's certainly evidence of very low budget construction, that lacks the durability of better quality materials. Fiberboard as sheathing isn't ideal, because of its susceptibility to rot and instability after being exposed to water. It also has little to no structural support, zero according to code.

It is bad? ... well, it's a crappy low budget material that shouldn't have ever met code in the first place, so yea. Are you screwed? No, not necessarily, just make sure you take protecting from water very seriously. Seal all exterior penetration properly, address any plumbing leaks immediately, ensure all wall cavities can dry, if you are adding any new insulation.

Can it hold a screw? No, I wouldn't even attempt to screw anything into it, it could in theory hold about what drywall would hold, using a hollow wall anchor like a toggler bolt. However I wouldn't even bother, if you have actual stucco on the exterior and not an acrylic stucco like finish, just anchor to that instead using an approved anchor. You'd anchor to drywall, if you were hanging something from the interior.

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