Thermal mass - plaster vs drywall

[Daox]

Just wondering how much you guys know about plaster and drywall as far as thermal mass goes. I did some googling and found the quote below. It seems plaster would be a fair amount superior. As I think about moving forward with my office project, I'm also weighing going ahead with plaster vs drywall. The room currently is almost entirely plaster and I wouldn't mind keeping the thermal mass it provides. This is what keeps my house cool during the day in summer without A/C. However, the additional insulation I add will surely help.

Next up, has anyone done plaster work? Is it a huge pain to do? I was hoping to maybe keep things simpler and go with a cement board and just a thin coat of plaster over it to retain the thermal mass properties, but reduce the amount of work. Ideas are welcome.


Thermal Mass | GreenBuildingAdvisor.com

Drywall can used as a thermal mass material, but only to a fairly limited degree. It has a density of 50 lbs/ft^3 and an R-value of nearly 1 per inch. This means that it can only hold so much heat/coolth, and you don't get a lot of benefit from multiple layers because the R-value is high (again, relative to context) so it will not tend to conduct heat to the deeper mass layers.

If you still think this is a good idea for your situation, I would recommend using a heavy-weight plaster over drywall. A cementious plaster can have a density of ~100 lbs/ft^3, and an R-value of 0.3 to 0.6 per inch. Both of these statistics make it a much better space-facing thermal mass material than straight drywall.