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Author Topic: Anyone tried building a solar kiln with R-Max, or other foam insulation panels?  (Read 2542 times)

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Offline Delawhere Jack

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Still tossing around the idea of portable solar kilns that I could rent out to milling clients to dry their wood. But running the numbers, a VA Tech type mill would weigh somewhere around 3,000 lbs empty. I'd like to have have a kiln (or kilns) that I could tow with my Jeep Cherokee, which would limit me to around 2,000 lbs.

The idea crossed my mind to use 2" foam panels in place of plywood and fiberglass insulation. It would still need sufficient framing inside to withstand wind loads while towing, but it should reduce the weight enough to make it practical to tow.

Any thoughts or experience using foam board to build a kiln?

Offline red

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You need to ask the people that build mobile Tiny Houses. . but they don't use Jeeps
We have a lot of good boys and girls in harms way
lets all support them and their familys.

Offline t f flippo

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Jack, How about travel trailer type constr. on a lite frame trailer.With jack stands when loaded with a charge ?

        Or, small boatbuilding composite constr. with foam in between the 'ribs'.

        Or, Ridged foam,laminate 3/4" stiffeners/ribs with a laminated 1/4"plywood skin

        Back to the first one. Old travel trailer/campers are cheap and easy to come by. Gut it.
        Foam sheets n 1/4" marine plywood on the inside.What you add would be less weight than what you
        gutted and tore out.

Best regards,  tc

Offline SLawyer Dave

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A lot depends on the temperature your kiln will operate at.  I built a passive solar food dehydrator, that uses 1" foam panels with the foil side out to help insulate and reflect the solar radiation.  Over all it has worked very well, but on really hot days, the edge of the foam directly beneath the tinted glass has gotten so hot that it has melted.  I try not to have the operating temperature above 135 degrees, (I don't want to cook the food), but in the actual collector area, I suspect the foam can easily get up to at least 150 -160 degrees. 

Hope that helps.
Dave

Offline Larry

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I used 2" foam in my solar kiln.  It was the kind used for concrete construction in cold weather and I got it for free.  I lined the kiln with 4" of the stuff and painted it all black.  The first hot day I looked and saw some huge bubbles developing in the foam from the heat.  To remedy that I covered it all with 3/8" sheathing plywood.  After doing that it worked great with no more troubles.  Ran it for a long time.

 
Larry, making useful and beautiful things out of the most environmental friendly material on the planet.

We need to insure our customers understand the importance of our craft.

Offline MattJ

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I made mine that way

http://www.forestryforum.com/board/index.php/topic,76042.msg1176560.html#msg1176560 

I used 1" foamular board and had no bubbling or other issues.  It has an outer frame of pine 1x2's.  It is very light, with the entire top being maybe 100-150lb.  The base is maybe a couple hundred.  It can hold ~500bf of lumber 10' long. 

I did recently upgrade the panels to dual layer polycarb.  I liked working with foamular, and it took paint easily.  If I did it again though I would use 2" like you are thinking.

Matt

Offline Delawhere Jack

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Thanks guys, your ideas have got the wheels turning in my head. Tom (tff), your idea about boat building and putting the panels between the ribs might be the key. The ribs could be fairly light, say 1x2's, and then an exterior 3/8" plywood glued and screwed to them for rigidity.

Dave, thanks for the heads up on melting the foam. I'll keep that in mind.

Larry, that really concerns me. I was hoping to limit the plywood sheathing to only the outside. Using it inside and out will mean a lot more weight. Could you tell if it was buckling due to expansion?

Matt, glad to see that you had no issues using foam.

Red...... If things slow down too much in the milling business, this kiln may become a tiny house... :D

Offline Delawhere Jack

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Doing a little research, it looks like the polyisocyanurate insulation has a higher service temperature. One company states 250F upper limit. Makes sense since this is what they use in SIP roof panels. A little cheaper than the blue or pink boards as well. Much less rigid than the blue stuff, but I can use inlet diagonal metal T-strapping to make up for that.

Offline Larry

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Larry, that really concerns me. I was hoping to limit the plywood sheathing to only the outside. Using it inside and out will mean a lot more weight. Could you tell if it was buckling due to expansion?

It could have been due to expansion, not really sure.  Looked like a basketball trying to push out between the studs.  It ruined a couple pieces of insulation, but I caught it before major damage occurred.
Larry, making useful and beautiful things out of the most environmental friendly material on the planet.

We need to insure our customers understand the importance of our craft.

Offline t f flippo

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JC, Your welcome. You got me thinking about honey comb panels. Like hollow core interior doors, skin stressed panels,ect.
     The modern boat building industry uses honey comb panels because of the high strength to wt. ratio.
     And there are a number of companies making hollow core/honey comb surfboards.

     I know an insulation company on the Western Shore that does injected foam insulation. They were very reasonable cost wise.

     Build a 4" x 6' x 14' panel.1/4" or 1/8" full size marine ply. faces. 1/4" x 4" stringers 12"oc inside. Inject with foam.
     And you have one side of your portable kiln.

  Come see me when you're down this way. We won't get any work done ,but have a good time talking about it. :D

tom




Offline Delawhere Jack

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Hey Tom. I might be heading your way in the next month or so. Cleanup day at Don's farm in preparation for hunting season will be coming soonl

Stressed skin panel is just what I was thinking...... After I read your earlier post. ;) Will probably need to be 2x material ripped to 2" wide. 1x I just don't think would give enough screw holding strength. Went and looked at the 2" foil faced poly foam at Home Despot tonight. Looks like is would work. I'll stop by Shone's tomorrow and see if they carry it. I'd rather buy local.

Hopefully, 1x3 horizontal strapping on 18" centers would suffice to stiffen the inside face of the studs.

I'd like to get this built by Sept 12th. I'm doing a demo at the local WoodCraft store that day, and it would be nice to be able to show it off. Looks like every other project will be put on the back burner for a while.


Offline t f flippo

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JC, Great ! I see Don's brother at the coffee shop, and long over due seeing Don. I live 10 min from there.

     You're trying to save weight; smaller scantlings for the frame and constr. adhesive or epoxy,staples or brads till the glue sets.
     The 'skin-stressed' eliminates the need for heavier framing.Depending what the 'skin' is and adhesive,ie.glue,epoxy,ect
     I need to get a better picture in my mind. The foil facing is throwing me off if trying to laminate it.

     I buy the blue ridged foam panels in Salisbury at a wholesaler. Much better price than the box stores.

     Sept 12th ? Why you startin' so early ?  :laugh: :) :D

Let me know if I can help ya,  tom


PS  BeenThere, Help! Where are you? You're always good on this technical stuff.

     
 

Offline GeneWengert-WoodDoc

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I wish to support the idea that some foam will not withstand the high temperatures in a solar kiln.

I assume that you figured the weight based on the Virginia Tech kiln.  So, let's look at each component.

Floor.  Can you maybe make the trailer floor and the kiln floor the same?  In other words, get some wheel for under the kiln similar to how a car is sometimes hauled on a small dolly.  The floor uses 2x6s due to the weight and also the rigidity.  With the handling of your kiln, you do need a very strong floor.  To save some weight, you could use hardware cloth on the bottom side instead of plywood.  Then you could use 3/8" plywood for the inside floor.

Walls.  The walls need to be well insulated.  The inner and outer coverings are often plywood for ease of construction.  You certainly could use 1/4" plywood on the inside, but it will warp and look poor on the outside.  Use plywood with an exterior adhesive.  Marine grade is not needed.  You could use 2x2 instead of 2x4, but that would cut your insulation in half, which would mean less heating and longer drying.

Roof.  We need framing for the roof to handle the expected wind, rain and snow loads.  It would be hard to get the full performance requirements with less than 2x4s.  The cover materials (two layers) is not very heavy and is essential.  There is no need to add a black absorber right under the clear collectors.  Rather, let the interior of the kiln, painted black, be the absorber.  This will not affect performance.

You might consider having the fans installed so they can be removed for transport, reducing the wight somewhat.

Another option is to make two smaller half kilns and then connect them into one kiln.  You would need two jeeps, trailers and drivers.  Or make two trips.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline MattJ

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When I bought the foamular insulation it was after a good amount of research.  Make sure you understand how it reacts with heat, what adhesives you can use, and what type of paint.  Foamular was pretty forgiving, another type I used before was not.  Can't remember the name but latex paint wouldn't stick and the adhesive I was using dissolved the foam.  Most of the manufacturers have pretty good info available.  In my first attempt I decided to wing it....and failed!

Offline Delawhere Jack

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Well, I'm committed now. Just bought a trailer to use for the kiln. It's the frame from an old Nimrod pop-up camper. A bit rusty, and I had to purchase new tires, but it should work. And the price was right. It uses 5.70 x 8 tires which barely extend above the plane of the trailer deck. I should be able to follow the VA Tech design pretty closely. I'll make some changes, like using 2x6 for floor joists instead of 2x8.  The kiln will actually overhand the wheels and act as fenders, so I'll have to header off a joist or two back at the frame for wheel clearance.

Can't get back to pick it up until Friday morning, which will leave me one week to meet my deadline.

Offline Delawhere Jack

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Gene,

Reading through your last post again. Lots of good advice, thanks.

I'll put the 2x6 kiln floor joists on the bare metal frame of the trailer, not on top of existing wood trailer decking. The idea for 3/8" floor in the kiln helps too. I could fasten skids on top of the floor aligned with, and screwed through to the joists underneath. I'll make them tall enough to allow loading with forks, say 3"? The corners and rafters will remain 2x4 lumber for rigidity, but where ever I can I'll use studs ripped to 2" to save weight.

I was looking at 1/8 tempered Masonite, prefinished on one side for the exterior. My concern is that tempered Masonite has an oiled surface, and may not bond well with construction adhesive. I'll need both mechanical and adhesive bonds to make this sufficiently rigid.



Offline plowboyswr

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I was looking at 1/8 tempered Masonite, prefinished on one side for the exterior. My concern is that tempered Masonite has an oiled surface, and may not bond well with construction adhesive. I'll need both mechanical and adhesive bonds to make this sufficiently rigid.




Have you thought about an aluminum or tin outer skin? We have a metal roofing supply place close to us that custom makes trim ect. that has sheet metal prefinished to your choice of color. Might save you some weight over wood and last longer than the Masonite. We custom made a garage door out of some back in 2001 and it still looks great. Just my two cents. Looking forward to seeing the build.
Just an ole farm boy takin one day at a time.
Steve

Offline Delawhere Jack

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It's coming along...slowly. Had to replace the ball coupler on the trailer, and now the trailer is soaking in phosphating solutions to remove some rust. After a little more measuring and figuring, it turns out I'll need to extend the main rails of the trailer 47" to carry the kiln. Thought I could cheat it forward some, and let it overhand the rear, but it just won't work. The main rails are 1/8" 2x4 rectangular steel. I'll add the extensions ahead of the axle.

The roof will be pitched at 40deg, which is correct for my area, and will reduce the height of the kiln by 12" compared to a 45deg roof. On the road height will come in at just under 10'.

It will be 4" shorter than the VA Tech kiln, but should still handle 12' lumber.

The foam I'll be using is foil faced both sides, so I'm thinking that if I really seal the interior exposed studs thoroughly, I can get by without interior siding. With generous allowances, it's now looking to come in at a little over 1,700 lbs.

Can't get the steel for the trailer until Tuesday, but maybe I can get started on the framing tomorrow. Looks like I won't have it done by the 12th. Oh well.


Offline Delawhere Jack

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Plow, I'm sure that would make for a great looking kiln, but it wouldn't give me the rigidity I need.

Offline GeneWengert-WoodDoc

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I suggest that you use plywood for the corners...maybe two feet width would be enough to increase the rigidity substantially.

Will you ever take the kiln off of the trailer?  If not, then certainly you should consider 2x4s for the floor as being adequate because the trailer also has a frame that would help.
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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