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Solar kiln construction

Started by MrMaple, August 30, 2021, 04:41:14 PM

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MrMaple

Hello I am new to the forum and have some questions regarding a solar kiln I'm working on. 

I have completed the floor and framing so far. It's a 15' by 6' footprint with an angle of 50 degrees since I am in central ontario.

 In looking at they VT design they state to sheathe both the inside and outside, but with plywood prices right now I'm wondering if I can get away with lap siding/board and batten right onto the studs using scrap, but sheathe the inside. 

I will be insulating with r12 bat insulation. Do I need a vapor barrier? 

Will 3 fans be enough for a kiln this size?

Also what kind of black paint/sealant should I use?

Just looking for tips on how to save some cash on this build. 

progress pic


 

tacks Y

I used a vapor barrier.

I used 2 fans on mine 3 may be better.

I used latex foundation coat on my inside and out. It does not melt in the heat being latex.

Just the way I did it but not an expert.

doc henderson

the inside needs to be water/moisture/vapor proof.  so a roofing or basement sealer is usually cheaper and best.  not sure I would want a tar smell, but it would already be black.  vapor barrier inside.  the better it is sealed, the more control you have over the drying of the wood.  to reduce the moisture gradient core to surface of wood, you keep the RH high initially in the kiln.  too many leaks and you will drop air moisture and have no ability to slow things down for species like oak.  the outside needs to breath so lap or board and batten is fine.  you can even do 1 x 6 boards at an angle for structure then lap over it, so any moisture in the insulation can vent to the outside.  the wall interior can breath.  if you are talking cheap box fans go for three, and they can be turned down as needed.  @GeneWengert-WoodDoc I think likes the aluminum sealant then paint black.  lots of info on the internet plans (which he helped develop) and on the NHLA website webinars (which he taught) detailing the goals of a kiln and drying wood theory that helps you make decisions about what is important.  some of it is for longevity.  you can dry wood under a clear piece of plastic.  but will need to replace from uv damage every 6 months or every month from wind damage.  frame looks good.  if pinching pennies, do it on stuff that can be upgraded later if needed, not on the insulation or interior sheathing.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

Cutter Lee

Can you please elaborate on the "inside" needing to be vapor tight, but the "outside" can breath? 

doc henderson

You will be putting wet wood inside, and using heat to evaporate the water into vapor that can be vented.  It will try to get out following a concentration gradient.  so it is trying to go from the wood chamber to the outside air.  Most insulation such as fiberglass, works by trapping air and keeping it stationary.  so decreases convection and transfer of heat.  wet insulation conducts heat and in no longer defined as insulation.  the moist air in the insulation will condense into liquid water at night.  so you need to prevent water vapor from the chamber "inside" from going through the interior sheathing into the fiberglass insulation.  any that gets through, needs to go on through the outside siding to the atmosphere.  so put your fiberglass with vapor barrier to the inside, then cover in plastic wall to wall.  then put wood over it to protect the plastic and paper.  then coat that with a water barrier such as aluminum roof coating.  touch that up any time you bump the wall and scratch down to the wood.  It seems like the wood is trapped between the plastic and the water proof coating.  I have asked that question or Dr. Wengert.   I have asked many of these questions.  He finally told me, "it is only a solar kiln!".   ;) :) :D 8)
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

doc henderson

Simple Solar Cycle Kilns at Timbergreen Farm

here is an example of how simple it can be.  I have dried stuff to 7% with just plastic.  but it does not last.  your kiln will be more complex (controllable) and last longer.  the more you "overthink it", the more expensive it will get, and some never get them done....hmmm.   :)  on the other end, is an insulated aluminum container with computer controls and costs 10s of thousand of bucks.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

farmfromkansas

I built a solar kiln last year.  Used 6 mill visqueen plastic on the inside of the studs, then sheeted with waferboard I had.  Painted the waferboard with the aluminum paint with tar mix, then painted with flat black. Do not put plastic on the outside of the studs, you need some air movement to allow your insulation to stay dry, just gaps between sheeting and studs will take care of it, and don't caulk the frame before boxing. My plan is to dry already air dried wood, and the wood doc says you don't need fans for that.  I put some in but will see what happens.
Most everything I enjoy doing turns out to be work

GeneWengert-WoodDoc

Good info here already.  Regarding fans...if you will not be drying green wood, but instead will be drying well air dried wood, two fans will be just fine.

When the kiln is empty, the heat will build up and can damage fans, so always open the vents wide open when not in use.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

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