# Experience based solar kiln operation.



## Poindexter (Mar 3, 2018)

I built some passive solar wood kilns, build thread here:
https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/

My state of the art design, mark 4, is here in that thread:
https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/page-5#post-2060948 

with a pic of modules 6, 7 and 8 further down same page form there, and dimensions somewhere inthe last tow pages.

Once I had those built, I had an operation thread running for a little bit, here:
https://www.hearth.com/talk/threads/solar-cord-wood-kiln-operation.152699/ 

Thanks to all who have contributed along the way.  Now that I have been running these a couple seasons I figure I can share what I have figured out the hard way and make it easier for the next guy/gal.

When I designed these, I knew they would work.  Now I can write, or start writing the manual.  I have seen a couple uninformed folks opine that running kilns "must" be a pain in the neck, but really it is just another opportunity to consume large quantities of liquor while the wife thinks a fella is doing hard labor out in the yard.  I can assure you I am going to kill a lot more limes for gin and tonics in blistering summer heat than I am going to get bruises out of this.

Let us begin, on 3-2-18, with # 7 and #8 empty.  I am currently burning out of # 6.

Here is 6-7-8 ribbed as built empty and with no membrane...https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/page-5#post-2064332 

It's one convective unit, one kiln, holds, ohh, 2.75 cords or so green. 

Today, with me pulling out of #6 for active burning it looked like this, right after I had two cords dropped in the driveway out front, roof shed snow shoveled out and the side curtain in #8 opened.  Todays pic is me standing on the stoop just outside the garage.  Top left is second floor deck,  tool shed back behind the raised bed hoop house, that SOB #5 to the right.





My biggest 'problem' with Mk4 framing is melted snow tends to collect between the three horizontal 2x4s at the top.  I could get out there with a broom and knock most of that off the tops, but I have had a melt recently.   I 'know' there is a bunch of ice up in there, if I get too aggressive with a broom I might tear the plastic, so better to just leave it for now.

I have a 'white' carpet in the stove room, so I try to handle as much cord wood as possible while I have good snow pack, less mud on the carpet that way.  The carpet might be ecru or eggshell or light beige or whatever, I only have a few crayons in my toolbox, white is the closest.  Happy wife, happy life. 

Sled is a good tool, though it is well above the floor level of the kiln today.




I did add some diagonal bracing to #8 and #7 and a few others already.  When six gets emptied I need to add some diagonals to that one.  Note the top edge of the outer horizontal 2x4s - the headache bars - is even with, same height as the lower edge of the 2x4s that make the floor of the upper level.  This will be important later, hopefully while the weather is still cool enough to get away with mere Corona before we get into serious GT and ice summer.




  Current chore is to fill #8 to the absolute gills, then finish cleaning up the splits in the driveway, likely enough to fill #7 to the gills as well. 

And empty #6.  Turn that knob on the side of the stove baby, you are wearing too many clothes to suit me.


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## Poindexter (Mar 3, 2018)

In a typical summer I will have light sprinkly rain in early May, hard hot sun in late May and through June, with serious rain starting in mid July, and continuing serious rain into Sept when the rain turns to snow.  I am not looking for a typical summer.  My plan is to get the wood in 6-7-8 dry (12-16%MC) muy pronto, and then keep it in the 12-16% sweet spot until temps drop to and stay below freezing.   

The wood I am loading is really heavy for spruce, probably close to 50% MC, well over the 35% max my reader will read.  The two hardest chores are going to be loading the fool things, and second dealing with summer's heat.  Pulling the snow back to keep water out of the kilns during the melt is on the easy-peasy list.


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## livetosail (Mar 3, 2018)

> I have seen a couple uninformed folks opine that running kilns "must" be a pain in the neck, but really it is just another opportunity to consume large quantities of liquor while the wife thinks a fella is doing hard labor out in the yard.  I can assure you I am going to kill a lot more limes for gin and tonics in blistering summer heat than I am going to get bruises out of this.



You, my friend, are a kindred spirit. 

Kilns look good. Show us more pictures! (I’m too lazy to look through the original threads)

So you are planning a step-by-step guide to show us how to make these? I stand by in anticipation!

Ps, where are you located?


Sent from my iPhone using Tapatalk


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## Woodsplitter67 (Mar 3, 2018)

Always a good read. Thanks for posting this.  We can all benefit from this and the pictures look great


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## Easy Livin’ 3000 (Mar 3, 2018)

Poindexter said:


> I built some passive solar wood kilns, build thread here:
> https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/
> 
> My state of the art design, mark 4, is here in that thread:
> ...


Love your pioneering spirit PD.

http://www.shelterlogic.com/shop/firewood-seasoning-shed-10-x-20-x-8-ft


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## Poindexter (Mar 3, 2018)

What I do with these things, the Mk4 design, is fill the offside to close to the top, then step in there standing on the nearside floor, and fill the upper deck, top bunk, honey moon suite, whatever you wanna call it, fill that without having to bend over much at all. , then refill the off side fromn the ground.

Looks like this with the top and offside full, ready to sweep the nearside and start filling that.




Then with the near side full to the gills, I get some crosswise pieces up in there on top.  Looks like this.




Now why the heck would I do that?  @ED 3000 is already at the head of the class, and can't be promoted further.  Would anyone else care to guess why i am taking this step?

It ain't because i can fit more wood in this way.  I have green wood in there, > 40%MC.  Looking at end grain, from the lawn, all the way up to and behind the headache bar horizontal 2x4.  Why would I put some splits on there turned 90 degrees with the bark facing out like that? 

I will post the answer in probably late May.

In the meantime the only thing left to do with #8 for now is to shovel out the snow from the floor framing..




Get the plastic membrane clamped as low as possible as above, then shovel the excess snow off from in front of #7 to in front of #8 - so the bottom edge of the membrane over #8 can't be hurt by the wind.




#8 is good for 6 weeks, maybe 8 weeks.  Go have a Guinness, its a lovely day for a Guinness.  I'll be busy filling some other racks, but for now my work here is done.


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## Poindexter (Mar 9, 2018)

Small problem, the melt is starting a few weeks early.  I was looking for +20dF in early to mid April.  +26dF today + solar gain = frost on the inside walls of the units with the green wood inside.




I have a small snow bank on the one side of the kilns as pictured in the previous post.  Shoveling that out to let air in at the bottom edge of each kiln is going to be easy-peasy.

On the opposite side, its on like donkey kong.




  Gonna take up a chunk of my weekend digging that out.  What I want to do is open the bottom edge of the kilns all the way around where the plastic membrane meets the floor.  That's going to let more air flow through, hopefully carrying out some water as vapor even with ambients below freezing - woot!!

I think the chain link on my back property line is 40".  It is more than 36, less than 48. 26 above and a shovel, Guiness weather.


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## Poindexter (Mar 16, 2018)

I got the south facing side shoveled out, at least far enough that melting snow won't be getting inside the kiln as liquid water.




I anticipate having all three cords loaded up mui pronto, I am getting into that part of spring time where the daily freeze/thaw thing is a PITA because there is so much moisture locked up in the snow.  Gotta get the last of the splits out of the driveway so i can fire up the weedburner to melt a channel down the driveway for melt water to flow in.


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## Poindexter (Mar 17, 2018)

I finally got the last one filled tonight.  Racks, unit, module, whatever, #s 6-7-8 are full.  I try to have all my wood for next season stacked on or before 03-17 every year.  

My #3 (nickname dam) is still empty, it is two spaces over from (that SOB) #5.  That is a different problem.  If you decide to build some of these, jump straight forward to my framing plan mark4 and skip all the preliminary steps that hold less wood and are a PITA (#4) to operate.

Daytime high today was +33dF.  I have 6-7-8 buttoned up for maximum temperature gain and minimum air turnover.  They are filled with all green spruce that was winter felled in the last 45 days or so, real heavy splits for their size.

I will try to not refer to the dam PITA SOB other builds from here on in.  

6-7-8 are full of green spruce way over 35% MC.  My first step is to get them down to FSP (fiber saturation point) (~30% MC) without letting the temp inside the kilns exceed ~+95dF.  

Tomorrow I will dig out the hard pack from the north side of 6-7-8.  Southern face (qv) is already shoveled out.  When my local daytime highs hit about +50dF I can look for about +70dF inside a buttoned up kiln.  

For now i need to go deal with the snow pack on my driveway before I have a puddle of really cold water under the laundry machines for the wife to complain about.

I'll post again here when I get to FSP or the kiln temps exceed +80dF.  For now the wood is up before spring melt really got rolling.


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## Poindexter (Mar 19, 2018)

I am right at +32dF ambient this afternoon.  I dont have a good way to get a thermometer into any of the kiln units, the snow is soft enough to be too treachorous for a ladder.

But i got ballooning.  It's warm enough inside there to raise the plastic membrane off thr pvc rafters, and i got copious water dripping down the inside...


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## Poindexter (Mar 24, 2018)

On the right is that SOB #5, chock full of splits i seasoned summer 2017.  On the left, separated by vertical plastic, is #6, just filled with green spruce felled March 2018.




Clearly the ice collecting on the inside of the left membrane is from water coming out of the green wood.  If accumulating frost was from melting snow it would be appearing inside both units, yes?

So far i have dried maybe 1 quart of water per stacked cord, 1600 pounds of water per green cord, stopping at 14 %MC, i got 687 quarts per cord to go... but my wood is already 0.15% done seasoning.

After that math problem, it's Miller time.


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## Poindexter (Mar 24, 2018)

Weatherman says it's +22dF today, feels about right.  This pic is from the other side, green splits right, seasoned left.


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## Poindexter (Mar 28, 2018)

I have 2 out of 28 possible of these already.


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## Poindexter (Mar 28, 2018)

I am thinking I could maybe open the vents a little more so I would have more water vapor pumped out and less ice on the inside of the membrane.  

Snow is too treachorous to climb a ladder out there just now, and opening the vents would lower the temperature inside the kiln, so I have to let it ride for now.


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## Poindexter (Mar 28, 2018)

FWIW end top vents at both ends are this big for three cords.




There is a bottle of tasty red waiting if you are with me so far.


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## Poindexter (Aug 26, 2018)

Summer 2018 I never did change a thing.  I spent most of June in the crawlspace under the house doing homeowner stuff.  Come August the clips were all in the same spots, didn't change the air outlets, nothing, just let it go.




With the lowest clips up waist high, chest high off the ground like that the wood up at the top is dryer than the wood at the bottom.  But as pictured mine will tolerate wind gusts of 35-40 mph without damage to the plastic membrane.  Lets a little water in if it is blowing and raining at the same time, but I am coming up with 10.5 to 11% from the stuff off the top of the stack and 15% MC from the stuff at the bottom.

I am calling it eight cords at 13% MC.  The only real work I did was stacking and shoveling the snow out from around the edges as the spring melt was starting.  Otherwise I have just been walking by watching nature take its course.  And running the string trimmer around the perimeter every second or third time I mow the grass.

Low impact, good results for 2018.  FWIW most of this was felled in Feb/Mar 2018, stacked by St Patricks Day 2018, I lit the stove August 26th 2018 with all 8 cords at 13% MC.  6 Months, standing spruce to excellent dry fuel.

This year I am going to reload the kilns as I burn and not stack everything in the last three weeks of winter.


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## kennyp2339 (Aug 27, 2018)

Thank you for doing this and documenting the whole process, this thread should go into the hearth catacombs


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## Woodsplitter67 (Sep 2, 2018)

How are you stacking the wood inside the kiln. I have had problems with my stacks wanting to fall over. I stacked straight but after some time it wants to start to fall over


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## Poindexter (Sep 5, 2018)

Woodsplitter67 said:


> How are you stacking the wood inside the kiln. I have had problems with my stacks wanting to fall over. I stacked straight but after some time it wants to start to fall over



As pictured in #6, #11 and #16 above, it all just lays in there with end grain showing.  The one exception is the lower two stacks are capped with perpendicular pieces to serve as shrinkage indicators.  When I can see the bark on the shrinkage indicators below the headache bar, I know my wood has shrunk, so I know the average moisture content is less than 30%, so I also know I can heat the kiln up as high as it will go without trapping water inside the splits.

My maximum horizontal run between verticals is 7' 5", an 8' long floor pad with upright 2x4 framing at each end.  What I have found is the longer the horizontal run of my stacks is, the more they sag as the wood dries.  The more they sag, the more likely to fall.  I don't know that I have ever been able to season wood in 12 foot long stacks at this location without having to restack at least once over the summer.  Six foot stacks at my location with local forest products rarely need to be restacked.

I am not claiming to be an expert stacker.  It is what it is.  By having uprights every 6-8 feet, I haven't had to restack at all since building this system.


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## Ashful (Sep 7, 2018)

Boy, your neighbors must talk...

“You seen what that Poindexter guy is doing this week?”


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## twd000 (Sep 10, 2018)

if you're able to get firewood down closer to 10% MC, rather than 20% MC as recommended, could you operate a catalytic woodstove with a lower exhaust temperature (higher overall efficiency) since you're not as concerned about creosote formation?


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## Poindexter (Sep 10, 2018)

twd000 said:


> if you're able to get firewood down closer to 10% MC, rather than 20% MC as recommended, could you operate a catalytic woodstove with a lower exhaust temperature (higher overall efficiency) since you're not as concerned about creosote formation?



My stove runs best with fuel at 12-16% MC.  

At 11% and under the (spruce) fuel off gasses really fast (burns hot) and doesn't have much left _gravitas_ left for a long burn.

It might be possible to design a wood stove to run on fuel at say 8-12% MC and burn clean and have low emissions and low creosote formation and etc, etc.  That stove would probably not sell very well as few stove buyers have got cords and cords of the stuff.

6-10% is another possibility, then the contractors building houses during construction booms could collect all the dimensional off cuts from building sites....

I suspect most of the cord wood stoves currently on the market are designed to run best at 16-22% MC because that is a pretty good national average for how dry wood can be gotten in a reasonable amount of time, and it is mandated for the EPA certification test cycle.


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## chemie (Oct 16, 2018)

Poindexter said:


> My stove runs best with fuel at 12-16% MC.
> 
> At 11% and under the (spruce) fuel off gasses really fast (burns hot) and doesn't have much left _gravitas_ left for a long burn.
> 
> ...



I looked at your pics and  skimmed through the thread! I don’t know what you are doing for a living but you are a very handy and smart person! I wish I could be that handy!
I don’t think I’d have time, skills, or space to implement your design. I have a nearby forest filled with storm fallen dead oaks. I cut 8 large logs last week. After the split, I got MC of 22-28 %. I placed them on a rack and cover them when it is rainy, otherwise I let them fully open. I am hoping they would go down below %20 before March so that I can use them in Spring shoulder season. Do you think it is reasonable for an Oak to lose about 7-8  % during fall/winter in NYC weather? 
About the solar kiln drying, for the coming Spring or Summer, do you think it would work if I cover 4X8 Landmand rack with a plastic cover like yours and adding some poles to the end to raise the top and opening some holes on the top to let oak obtained from fallen dead trees to be seasoned from %28 to below % 20? It is humid during summer months though.


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## Poindexter (Oct 17, 2018)

@chemie, the main thing about solar kilns is getting the solar gain to raise the temperature inside the kiln.  That lowers the relative humidity of the air in the kiln, increasing the diffusion gradient between the damp wood and the drier surrounding air, so the wood dries faster.  It's all abotu EMC, equilibrium moisture content.


I have been PM-ing user @Woodsplitter67 diligently for him to start his own solar kiln thread.  He is back east, deals with hardwoods, and bang for buck he kicked my butt with his simple and inexpensive but effective build.


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## showrguy (Oct 17, 2018)

Poindexter said:


> @chemie, the main thing about solar kilns is getting the solar gain to raise the temperature inside the kiln.  That lowers the relative humidity of the air in the kiln, increasing the diffusion gradient between the damp wood and the drier surrounding air, so the wood dries faster.  It's all abotu EMC, equilibrium moisture content.
> 
> 
> I have been PM-ing user @Woodsplitter67 diligently for him to start his own solar kiln thread.  He is back east, deals with hardwoods, and bang for buck he kicked my butt with his simple and inexpensive but effective build.


I'd like to see that too Poindexter..
I've been through all your solar kiln thread stuff, pretty impressive ..
I'm in hardwood country as well, so hopefully @Woodsplitter67 will enlighten us with his setup ??


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## Woodsplitter67 (Oct 17, 2018)

So i haven started a thread on my kiln or experience  because i felt that it was a waist of time. That people really werent intrested. @Poindexter... i will start one. I did a little posting in one of your threads. The response was anything but great.. i will do it.. i have my kids sports tonight and tomorrow but will put somthing together..


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## showrguy (Oct 17, 2018)

Woodsplitter67 said:


> So i haven started a thread on my kiln or experience  because i felt that it was a waist of time. That people really werent intrested. @Poindexter... i will start one. I did a little posting in one of your threads. The response was anything but great.. i will do it.. i have my kids sports tonight and tomorrow but will put somthing together..


I'm already interested !!


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## chemie (Oct 17, 2018)

showrguy said:


> I'm already interested !!



Me too! I hope it would be suitable for not so much handy person without much space only four 4X8 Landman racks


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## Poindexter (Oct 17, 2018)

Woodsplitter67 said:


> So i haven started a thread on my kiln or experience  because i felt that it was a waist of time. That people really werent intrested. @Poindexter... i will start one. I did a little posting in one of your threads. The response was anything but great.. i will do it.. i have my kids sports tonight and tomorrow but will put somthing together..



I am looking forward to your thread whenever is convenient for you to post it.

Your results are either as good as mine, or better, and you spent a lot less money on kiln materials then I did.  Yours is the better design.

I think folks who are curious about maybe trying to kiln dry part of the stash are a lot more likely to drop, what 40 bucks or so per cord like you did.  I think one reason folks aren't duplicating my build, even though my results are good, is I spent close to $300 on materials for each cord of kiln capacity, and did all the labor.


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## Woodsplitter67 (Oct 18, 2018)

The hardwoods solar kiln thread is started.. i hope this helps someone


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## Chas0218 (Oct 18, 2018)

Poindexter said:


> My stove runs best with fuel at 12-16% MC.
> 
> At 11% and under the (spruce) fuel off gasses really fast (burns hot) and doesn't have much left _gravitas_ left for a long burn.
> 
> ...



You're correct about the 6-10% off gassing fast. I built my 2nd story addition (added 2nd floor) and 2 story addition and burned all my shorts the kiln dried lumber didn't last long but did produce a good amount of heat. The secondary burn lasted 2 hours and from start to coals it was 5 hours. This was in my big stove and outdoor temps were in the mid 40s. Either way it burned fast compared to my poplar that is 20%-25%. I can get a nice 8 hour burn out of the stove loaded with poplar.


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## Easy Livin’ 3000 (Oct 21, 2018)

Woodsplitter67 said:


> The hardwoods solar kiln thread is started.. i hope this helps someone


Am I missing the pics? Poindexter had loads of pics.


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## Ashful (Oct 22, 2018)

ED 3000 said:


> Am I missing the pics?


Here you go, Ed.  Woodsplitter ain't as verbose as Poindexter, but he knows how to build a kiln!

https://www.hearth.com/talk/threads/solar-kiln-for-hardwoods.170518/


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## Poindexter (Mar 16, 2021)

New problem the last two years.  I found out (by accident) that I could load a cord of wood with a wheel barrow in about two hours, compared to about a week of free time with a sled.  But the wood I loaded with a wheel barrow came out of the kilns moldy, and my wife is significantly allergic to mold.  This was 2019 seaonsing

The second time I loaded my kins with  a wheelbarrow (spring 2020) I left the plastic end caps off my kilns to promote airflow, sprayed all my framing down with concrobium, replaced all the plastic membrane, and it didn't help, still pounds of black mold. 

So this year I have all my wood for Sep 2021 stacked and in the kilns before Saint Patrick's Day 2021, with end caps on.  

Your climate is probably different than mine, and you and your spouse may or may not have mold allergies.  This is just another variable.  I won't "know" until September, but my hypothesis is splits I bring in after 'the melt'  have been warm and wet for  a while, allowing atmospheric/ endemic mold to take hold, where the splits I previously brought in and kilned before 'the melt' were too dry to support mold growth once it was warm enough in the kilns for mold to take hold.

FWIW my daytime high today was about +10 dF, but I have enough solar gain that the green wood I have in my kilns is giving up water, as evidenced by the condensation on the insides of the membranes on the kilns. 

I will post again in Sep 2021 with my results, but I am well accustomed to producing splits that could grace the cover of many magazines


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## Woodsplitter67 (Mar 18, 2021)

Poindexter said:


> New problem the last two years.  I found out (by accident) that I could load a cord of wood with a wheel barrow in about two hours, compared to about a week of free time with a sled.  But the wood I loaded with a wheel barrow came out of the kilns moldy, and my wife is significantly allergic to mold.  This was 2019 seaonsing
> 
> The second time I loaded my kins with  a wheelbarrow (spring 2020) I left the plastic end caps off my kilns to promote airflow, sprayed all my framing down with concrobium, replaced all the plastic membrane, and it didn't help, still pounds of black mold.
> 
> ...



something is different.. you did this for a period of time with no issues.. then as of late your having mold.. Your very experienced with this so I'm in no way telling you what to do.. Mold will crep in due to the lack of ventilation if your seeing moisture on the inside then I would personally vent more ... or wait and not wrap your kiln right away. All wood will lose a significant amount of water right after splitting so if you let it dry some I don't think that it will put you behind in the seasoning process...


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## Poindexter (Mar 18, 2021)

Woodsplitter67 said:


> something is different.. you did this for a period of time with no issues.. then as of late your having mold.. Your very experienced with this so I'm in no way telling you what to do.. Mold will crep in due to the lack of ventilation if your seeing moisture on the inside then I would personally vent more ... or wait and not wrap your kiln right away. All wood will lose a significant amount of water right after splitting so if you let it dry some I don't think that it will put you behind in the seasoning process...



Thankfully I keep pretty good notes, err, umm, take pictures of my wood piles and keep them in my phone.  I had no trouble at all until spring of 2019 when I didn't have my wood up before the melt and kept my kilns closed up pretty tight.  I brought a bunch of wood in in May/June 2019 as green splits, and discovered it was much quicker to load the kilns with a wheel barrow.  I left the end caps off to promote airflow and got moldy wood out in Sep 2020.

For May 2020 I know I was tied up with 'rona stuff at work but loaded again with a wheelbarrow - after replacing all the plastic membrane and spraying down the kiln skeletons with Concrobium (tm).  And I got mold again.

For March 2021 (it was I think -22 dF ambient the morning after I finished loading), I have all my wood stacked in the kilns before the melt and I got my end caps back on.   Every seasoning yard is different, just because a thing works at my house doesn't mean it will work at your house.


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## Poindexter (Jul 5, 2022)

Been a while.  Just reviewing, in winter 2020/21  I loaded my kilns on hardpacked snow with a sled and had no concerning mold on my finished splits in winter 21/22.  I was done loading for 22/23 in March 2022 and currently have no visible mold.

Local to me, if I load up green splits with a wheelbarrow after the snow melts (n=2) I finish with mold.  If I load during the winter with a sled n>=4), I have no mold to speak of on the finished splits.

YMMV, blah blah.


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## Woodsplitter67 (Jul 5, 2022)

so what do you think the difference is..


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