I'm building my solar kiln and thinking about the interior wall. I was planning on using cdx plywood with a roofing paint as a moisture barrier. With the price of plywood what it is, I thought black 6 mil plastic might be cheaper.
Would it be a mistake to use black plastic instead of painted plywood?
I plan to use fiberglass insulation if that makes a difference.
I would stay away from the fiberglass. Moisture will be an issue.
i am not sure what you mean to replace plywood and paint with plastic. you need something to support you vapor barrier whether it is plastic or paint. it could be solid wood, but it will degrade if constantly wet. so, the wood (whatever it is) is to support a moisture barrier. so, guys used to put the basement foundation coating on a foundation and then press the 6M plastic into it. but it loses its elasticity and will eventually crack if there is an underlying crack. plastic alone will not last as you will surely poke holes in it loading and unloading. the key if you use fiberglass is to block the humidity (water) from the inside (vapor barrier) from getting into it, and poss. letting the outside breath. so, board and batten or lap siding better than solid 4 x 8 sheathing. who can afford that anyway?
Good point on the durability (or lack thereof) of using only plastic sheeting and no wood support as a moisture barrier.
Looking around some more, I saw asphalt impregnated board.
How would this do as an interior wall sheathing?
https://www.homedepot.com/p/1-2-in-x-4-ft-x-8-ft-Southern-Pine-Asphalt-Impregnated-Board-A11230848096/206086210 (https://www.homedepot.com/p/1-2-in-x-4-ft-x-8-ft-Southern-Pine-Asphalt-Impregnated-Board-A11230848096/206086210)
that is a neat product for managing the water and you should be able to reinforce the seams and roll asphalt over it. the trouble is if you bump it with a load of wood on tractor forks, will it poke a hole in it. It looks like the sheathing that used to go under siding. go look at it and press a fingernail into it. may still need some wood over it to protect it from abrasion and bumps.
A solar kiln doesn't need to be moisture tight, after all, the vents are always open while it is operating. The insulation must be kept dry, to maintain its effectiveness, so that's the main reason for any moisture barrier. Actually, my solar kiln is board and batten outside from my sawmill, very loose and not sealed, and the main thing is that moisture doesn't get trapped in the walls, so they need to be more moisture repellent inside than outside, so moisture can easily escape. It's also 1/4 plywood on the inside.
As noted by Doc, the inside will be taking hits and impacts while loading and unloading, so the inner wall needs to be pretty strong.
If I was trying to build one with solid wood, I would put some Tyvec over the studs on the inside, and layer on some saw mill wood, something not prone to rot, such as white oak, sassafras, etc. Then glop on a thick layer of asphalt yuck paint, including the floor, and be done with it.
Just a random thought but what about 2" thick foam insulation with rubber sheet glued to the face?
Cheaper than wood, nothing to rot and lightweight. But I am also not sure what interior wall you are talking about. I thought kilns were wide open inside? minus the baffle wall that has the fans in it.
I went CDX, and would do so again, for structural integrity reasons. I've moved my kilns around with skid steer and palette forks, and will probably do so again.
The exterior walls are stud walls, typically plywood facing the inside, insulation between the studs, and an exterior, breathable wall.
you have to check to see that the foam will tolerate the temperature. the cheaper foam may not have the temp rating as high as the more expensive stuff. the interior wall refers to the inner skin of the exterior wall.
ahhh, that makes sense. Thanks guys :)
If you use fiberglass with asphalt coated paper as a vapor barrier, put it to the inside. the outside siding should shed water but allow vapor to breath out through the siding. lap siding or board and batten. as @GeneWengert-WoodDoc (https://forestryforum.com/board/index.php?action=profile;u=20498) once told me, it is just a solar kiln. if you think too much you will never build it. like me. :) closed cell is better than open cell for spray, and i think the harder board foam, is better than the softer. I think it is polystyrene. the hard may be a polyethylene?