Solar Kiln for Reclaimed Lumber?

[Warren]

Good afternoon.  Dabbling in the wood world after a multi-year hiatus.  Acquired a pile of reclaimed lumber, pine and hardwoods, to mill into flooring.  Has been in storage for approx 20 years.   Know that some of it has/had bugs.   Assuming that all of it does. Currently checks at approx 12% MC.  Two questions:

1) Planning to resaw to 1" nominal thickness before mill work. How long to dry from 12% MC to 8% in a Virginia Tech style solar kiln?   Thinking that it should go fairly quickly.   But do not want to assume.

2) Reading that sterilization may or may not be 100% effective with solar alone.  I like the idea of holding 150*F for 24 hours if possible.    Can the VT solar kiln easily be outfitted with some type of external supplemental heater (preferably wood burning) to maintain sterilization temps for 24 hours, without "killing" the kiln internals  ?

Open to suggestions.   Planning to process 3,000 to 4,000 bd ft of material.   Thinking of working in batches of 500 to 1000 bd ft of material per batch.   All help gratefully appreciated...

[KenMac]

I'm sure that you will get several great replies on this, but you can also use the search function to find most of the answers you seek. Good luck!

[doc henderson]

Well sounds interesting.  I think the time to dry depends on where you are starting from and what species.  soft wood can go fast and harder stuff like oak needs to go slow.  In a solar kiln to go slow you can cover part of the collector or load it fuller of say oak to go slower.  the heat treat can be in a solar kiln, but you may lose heat at night via the glaze that lets in light but if single wall, not efficient at storing heat.  If you want it cheap, then tell us what heat source you already have or have or have in mind.  For heat treat some just add 4 work light with heat producing halogen bulbs.  If you have tuftex and rigid insulation, you need to check the high temp rating.  the walmart box fans if used can be removed.  at night you could cover the clear glazing with moving blankets to insulate the kiln to hold heat better at night.

If these are timbers (you did not mention the dimensions) and you are resawing them smaller, it is possible that the interior is wetter than the outside.  did you use a pinless meter on the surface? 

is there frass on the wood in storage indicating bugs?

[Warren]

First picture of the cants that have been bundled for past X years.  Second picture when I open some of the bundles.   Other bundles solid.  No issue.   However, assuming where you have bugs, everything has  bugs.

In re: fuel for heating?   I am assuming I have several bundles of cants like the ones below, thinking burn the infected cants to heat sterilize the resawn lumber, after solar drying, before milling.  Make sense?   

The idea of hanging incandescent heat lamps in the solar kiln for several days to maintain the heat does tend toward the Easy Button...

Mix of lumber is about 50/50 pine vs mixed hardwood.  Moisture measured with Delmhorst pin meter.   At this point, if I targeted all oak, should be no problem for pine.  Not so?

[doc henderson]

I guess the question is do you already have a wood burning heat source.  If not, after regs have raised prices, a wood furnace is maybe 2k bucks.  you could put a wood stove in.  If you have none of the above, then you would be better to get halogen work lights at HF and heat it for 24 hours.  



here is a wood furnace firebox to air exchanger with a fan.  got it for 250 bucks but a new one is 2k.  for 4 sessions of 24 hours the lights seem the most resonable.

[doc henderson]

are the inner cants as dry as the outer surfaces?  Is it just one species eaten up or all?  what are the dimensions?  are the bugs all the way through or just on the surfaces?  bugs that like soft wood may not enter hardwoods and depends on the moisture content.

[Warren]

Seems to be more prevalent in the pine than the hardwoods.  Cants vary from 4" x 6" to 6" x 8" cross sections with lengths 4ft to 10ft.    Most cants were bundled 40"-48" width, 24"-36" tall.

Outside of all of the cant bundles appear to be "good" condition (like my first picture above).  However, when I open the bundles, some of the bundles are fine, sound and heavy all the way through.  Other cants look like my second picture above.  Bug tracks / rot throughout.   Very light weight.  

The oak cants appear to be "least" affected.  However some bundles of oak appear to have been affected as well.

Given that we are coming into summer, looks like I should be able to snag a workable used forced air wood stove in the $200 to $500 range. 

And "Thank you" for the help and assistance.  Much appreciated!

[beenthere]

Hope you can recover the material you want for flooring but think the first 2-3 bundles you saw up will give you a good idea whether you want to go to the drying stage, or if it will just not be worth the effort for what you can recover. 

[YellowHammer]

An inexpensive wood stove is a good solution for a solar kiln to provide additional heat, maybe even a conventional DH kiln.  I didn't realize there were getting so inexpensive, I may have to do it myself.  

Easy, cheap heat is the key to "no question" sterilization.  When in doubt, leave it in a little longer, and there is nothing better than seeing dead, charcoaled bugs laying on the floor.    

[doc henderson]

I think that is a used price.  they used to be 700 bucks new, and now at least double typically here.  I paid 250 $ used.

[scsmith42]

Hi Warren, it's good to see you posting again.

At 12% oak will require around a week in a solar kiln to come down to 8%.

With pine, Gene Wengert used to tell us that the industry standard was not to dry pine below 12%, as it would tend to have a lot of tear out during the millwork process unless the tooling was extremely sharp.  So you might just want to put whatever pine your process through a sterilization only cycle, and not dry it more.  Usually you will lose 1 - 2% MC during sterilization anyway.  As buggy as that pine is, I would not recommend that you use it for flooring.  Pine is soft and when it has had bugs in it there is a tendency for wood cells to collapse under foot traffic.

IMO, The only problem with using a woodstove for solar kiln heat is keeping the darn thing stocked up overnight.

I opted to use a propane forced air heater instead, so that I could sleep!

A wood stove with a forced air system sure would be economical to operate though.  Need to figure out some type of way to auto-feed wood into it overnight...

[doc henderson]

next time a neighbor upgrade to a newer more modern furnace, offer to take it from them.  I have a furnace in my shop (NG) but I only use it for AC.  I have a boiler and in-floor radiant for heat.

the exhaust from a propane heater will add some moisture to the kiln.  better to have a heat exchanger.
for heat treating for 24 hours, not as big a deal.