On 10/24/2011 12:17 PM, Dave Platt wrote:
I have a sauna with electric heater 7000watts. Nice area on top to put some
rocks and I see others have suggested lava rocks. What if I put granite or
limestone? That is what I have there now, they haven't cracked or exploded
after spraying water on them. They look nice, some red, some different
colors. Is there any harm in using granite or limestone apposed to using
lava rocks? I am sure they were all the same a few million years ago,,, any
reasons why I shouldn't use the granite or limestone rocks? Radiation?
Emmisions of sometype? inevidable that they will explode?

Not inevitable, but entirely possible, and with potentially bad
consequences (e.g. "flying hot rock fragment puts out somebody's eye").

Granite *may* be safe enough, as it's a metamorphic rock which has
been heated to high temperatures at least twice in its lifetime.
Depends on whether that particular granite has cracks in it (some
does), how much moisture or water it has been exposed to, etc.


granite is igneous. gneiss is metamorphic from granite.

The hazard is, as you point out, voids full of water that superheat, and
then flash to steam. Sort of like the spalling from lightning current
flowing through corroded bolts in concrete.

So it depends more on the structure of the rock than precisely whether
it's igneous, sedimentary, or metamorphic.



I would avoid limestone, as this is a sedementary rock which is
deposited from water and has quite a bit of water bound up in its
structure.

It's really a question of "How lucky do you feel?"