Solar Kiln Insulation^ and Vapor Barrier Materials

      Closed-cell foam insulation and plastic vapor barriers are necessary to withstand a kiln interior's moisture load. August 21, 2006

I read that when insulating a solar kiln or any kiln, you should use a closed cell foam insulation with Krona brand vapor barrier and 3m 8951 tape, then put in your inside covering with a coat of aluminum paint, then paint everything flat black. I priced foam sheets, and closed cell is double the price. Do I really need closed cell foam?

Forum Responses
(Sawing and Drying Forum)
From contributor C:
The purpose of a kiln is to remove gallons of water from wood in the form of water vapor. The purpose of closed cell foam is to prevent it from absorbing water and becoming saturated. Open cell foam has a tendency to absorb water vapor and break down. Yep, I think closed cell is a requirement.

From the original questioner:
My question is with a vapor barrier like aluminum paint or Krona before the insulation. Do I need closed cell insulation?

From Professor Gene Wengert, forum technical advisor:
The vapor barriers help, but they are not perfect (they get holes, etc.). Yes, you do.

Incidentally, the Krona vapor barrier is not necessary. Use plain, ordinary plastic and it will work just the same. The heat reflection is not an issue here.

From the original questioner:
So I should use plastic and aluminum paint? I read about just using aluminum roof paint. Should I paint flat black over the aluminum paint?

From Professor Gene Wengert, forum technical advisor:
Aluminum roof paint is okay, I suspect, but it depends on the brand, etc. Black on the inside is essential.

From the original questioner:
I have just found something called Silverline made by Pace Products. Is this good?

From contributor I:
Why is black paint on the inside essential?

From the original questioner:
If you painted the inside white, it would reflect sunlight, not absorb it. Instead of foam sheets, could I use spray foam - is that closed cell?

From contributor D:
Silverliner is good stuff, but reflective.

From the original questioner:
I was thinking of painting it black.

From contributor D:
Spray foam is good, but it has to be done correctly. There are special requirements for kilns. You cannot use the foam kits that are sold for DIY use.

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