Paperless Drywall as Hearth Board

[KWillets]

I got curious the other day and started looking at the specs for (broken link removed). It's drywall with the combustible paper facing removed and replaced with fiberglass web. It's classified as noncombustible, and some types are used in firewall-type applications. It's starting to appear at the big-box home improvement stores.

Drywall has an R-value of .45 per 1/2", so it's about two times better than Durock. It's not particularly hard, but I suppose it might work bare, or covered with metal or some such, or tile.

Would this make valid hearth protection? My stove manual simply says "noncombustible with an R-value of .446 or better". It doesn't seem to require fireproofness (drywall breaks down under fire conditions, absorbing heat and giving that 1-hour fire rating).

 

[KWillets]

Same thing - fiberglass. The paper is removed to prevent mold.

From what I've read, the only reason that ordinary drywall is considered combustible is the paper facing -- without it, it can be placed near combustion appliances, etc.

 

[Jags]

From what I've read, the only reason that ordinary drywall is considered combustible is the paper facing -- without it, it can be placed near combustion appliances, etc.

That is true. The paper simply stabilises the interior, which is simply made from a gypsum slurry (rock).

Note: much of the drywall today is synthetic, made from the waste coke from coal fired power plants.

 

[begreen]

I suspect it would not make as good a backer as cement board for tiling, especially for a horizontal surface with a lot of weight on it. But check with the manufacturer, I could be wrong.

 

[KWillets]

I just dug up a paper on breakdown of drywall under heat. The majority of breakdown occurs between 100C and 200C. Would that ever occur in normal stove operation?

The old tile-on-drywall technique is a classic of contractor cost-cutting. Our upstairs shower is made of it . True, it might not make the best floor, but a hard covering helps. There are a number of gypsum floor leveling products.

 

[webbie]

I have seen "approved and listed" hearth boards which were made of ceramic tile glued to 5/8 fire code drywall - which does have paper. If this passed, then I would assume the paperless stuff is fine too. The main problem with some drywall is the relative softness of it - but as one layer in a system it is probably fine.