Here is a piece of wall I broke open. Fiberboard backing was nailed to joists with plaster (grey) and a skim coat (white). New Jersey house built 1896 and renovated many times since. Original walls are wood lath with plaster. Most recent walls are straight up drywall. But there are walls made with various materials and this is one of them.

What are the years this would most likely have been used?

The grey/white diagonal lines in the plaster are from my saw so don't look there for clues. :)

enter image description here

Edit:. A little further research. Fiberboard also called Celotex, Insulite, beaver board. My house was built in 1896. First fiberboards were invented/patented between 1901 and 1916 so even if the first major renovation were after 10 years it's possible this material could have been used. More likely, during the 20s, 30s, or later. I'll add my own answer with this info once I've learned a little more, hoping to learn more from all of you.

2 Answers 2


I just worked on a house over here in NW Washington built in the 1930's that had that on the outside walls, the interior walls were rock lath and plaster.

  • 1
    I had that in my previous home, that was 1941 construction. Beautiful, glass-like rock hard plaster finish over rockboard. I think 1930s/40s was the heyday for plaster over sheet material.
    – jay613
    Commented Dec 19, 2021 at 17:51

We still use that system.

It’s called “Thin Coat Plaster”. We use it where we want an extra hard surface as a finish… like a school corridor. It’s fire rated and prevents the walls from being scratched up.

  • I'm aware there are various plaster surfaces that have desirable qualities and appearances compared to drywall but I believe in modern use they would be applied over rockboard or cement board, not the kind of board in my picture that I think today is most commonly called "beaver board".
    – jay613
    Commented Dec 19, 2021 at 17:49

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