kiln wall insulation

xlogger · November 04, 2015, 06:57:10 AM

I hope to get started soon as the rain stops on my new kiln. I see where I can buy some 2" polyiso foam boards for a good price, that says it has foil on both sides for a moisture barrier. I was going to build the walls with an 1/2" insulation board on the inside with the moisture barrier there, insulation in the walls and a 2" foam board outside. Would it hurt to have the outside with this board with foil on both sides also? I am planning on covering the outside board with wood panels probably board and batten. Also could I use this 2" polyiso boards under the concrete floors?

WDH · November 04, 2015, 07:14:09 AM

I believe that the foil backed foam, polyisocryanulate, if used on the outside under the board and batten, could trap moisture in the wall since you will also have a vapor barrier on the inside. You can get 2" polystyrene that does not have the foil backing, and use this on the outside.

xlogger · November 04, 2015, 12:59:18 PM

That's what I was planning on doing but saw this on CL for about 1/2 price.

Saga Dan · November 04, 2015, 02:51:45 PM

I would not use polyisocyanurate insulation under you slab. It will absorb moisture, break down, and become useless. Use an extruded polystyrene with a high enough psi compression rating for your under slab application. It will not absorb water and will stand up the the compression of the slab and building above it.

xlogger · November 04, 2015, 05:34:51 PM

I hear you, thanks

Cazzhrdwd · November 05, 2015, 08:52:19 PM

I had spray foam sprayed in, makes a great moisture barrier. Its a little pricey but works wonderful.

CedarDude · November 07, 2015, 12:13:54 PM

Not sure if this is a solar kiln or not but there is the issue that rigid foam board starts to lose integrity (melt?) at 165F so application on interior walls could be an issue? That said, I've seen posts by folks saying they have used rigid foam in their kilns with no apparent problem.

Tree Dan · November 11, 2015, 07:58:54 PM

I would frame it, then call in a contractor to spray it.
It will cost a little more, but you will be glad you did if you want a no draft great R - Insulation.