Thanks, Bill, Oakie. That 8" on-center OSB paneling really complicates things if you want the seams to match and the edges to rest on studs. The first full kiln load will be some oak I cut last year, a mixture of red, white and black oak. I'm currently involved in a walnut cabinet project and would like to reduce its moisture content a tad, so that small bit of walnut may preceed the oak.
Here's the last pics. Got a mostly 8' load in and started it up last evening. To make the recommended proportion of collector area to load, I hung a 2' wide silver tarp under the glass across the bottom this morning.
The black tin on top of the lumber collects solar heat. The black baffle seen in the following photo also collects heat and directs blown air down over the collector panels. The air then flows down the opening in the front and back through the sticker spaces in the pile.
I put the vents on the inside of the kiln; maybe not the best idea, but I didn't want to get the ladder out every time I needed to adjust the upper openings.
There's 1/4" hardware cloth in the front of the vents to keep out birds and some insects.
This is only a suggestion from my past experience, I cut a 10x12 tarp in half and folded in to what ever size I needed to hang on each end of the wood pile in the kiln and weighted it down with a brick to more efficiently force the air through the stickers on the pile and did not loose air through the gap at the either end. You can just lay it over the collector and weight it down and then weight it down to the floor. It surprised me how much more it efficient quick the drying process was. Hope this helps. It took me 2 attempts on my own kilns to get it right and then several I built for others, yours looks like you have been building them for years, great job!
Thanks Oakie, Citrafarm. I stuck pieces of siding at the ends near the front to prevent air flow around the pile. Yours, however, may be a better way - more flexible. Anyone got any guidelines on what and when as pertains to the vents?
Well, it's been 7 days since I put in the load @12-14% moisture content (oak previously air-dried from last year). I'm too lazy to follow the correct procedure of cutting sample pieces and weighing them every day, so I'm using a moisture meter. My testing now indicates 6-8% (oops: forgot to adjust for temperature; will have to do that). I hope that's not drying too fast, but I don't see any sign of cracking or checking. The vents are almost closed now and the kiln temperature yesterday was 130 degrees at 4:00 pm.
I never used the weighing method either, I am lazier than you. I used a moisture meter also. Your drying time seems about right, I put green white oak in once at about 35% moisture and in 30 days it was about 6 to 8% but since I did not air dry it, it cracked and checkered. I began air drying for about 6 six months in the Oklahoma heat, then put it in the kiln at about 14 to 18 % moisture and got it down to 6 or 8 % with fantastic quality. It took about 2 weeks to get it to 6 to 8% so yours sounds good. It is better to dry slowly let the wood condition itself by absorbing humidity and drying slowly thus cutting down on cracks, warping and checkering. You will learn how to measure the time in the kiln based on your weather and humidity in your location. Good Luck
Drying too fast is also said to cause "case hardening" - from a book I read one time. Leaves residual stresses that may not be apparent until you thickness plane, at which time new warp and curl problems arise. I'll be interested to see if this happens in our lumber, but first we have to get back to working on the kiln. Work pressures for both of us have left us with precious little discretionary time recently. Frame is up, structure is awaiting black paint on appropriate surfaces, glazing, and roofing of the back slope.
I believe we are talking about the same thing, drying slowly allows the wood to "condition" which is to dry and absorb the humidity at night and repeat the process over and over slowly so it does not curl or crack, the same is true with concrete, that is why you have to keep it moist while drying. Anyway a old time "sawer" told me that solar kiln is 10 times better that electrical heat because it forces you to take it slower. Commercial kiln lumber has a far greater loss in quality board feet but has 100 times the production because of speed.
I expect we are, I just threw in the descriptor in case it rang a bell. I also expect you are right, commercial (or even agressive hobby) drying is all about shortening the cycle. If you don't extract at extreme rates, it would seem less likely to do harm. I have a pile of 15% lumber, but I also have quite a pile of soon-to-be-fresh-cut lumber. I could throw the greenest wood in the kiln first, to dry it quickly, but I suspect that won't be satisfactory. I'll more likely dry the fresh stuff for a year in the air, then kiln it when my pal wants to use it. Big problem will be getting him to predict his needs far enough in advance to allow kiln drying off-season.
Gene Wengert, kiln drying expert, says "casehardening, also called drying stress and tension set, develops very early in drying." Therefore, I'm crossing my fingers that it won't happen to the previously air-dried lumber I'm practicing on in my new kiln. Only time will tell. Even though I started this thread, it is open to anyone who wants to post pictures of their solar kilns --- hint, hint.
My load of oak dried to 6% moisture content from an initial 12-14% in 11 days. I removed it from the kiln this morning and found no evidence of degrade. I'm convinced this design provides a safe means to quickly and cheaply dry lumber. Killing bugs, I don't know. The highest temperature I recorded was 134 degrees behind the lumber stack at the back of the kiln (inside), so I'm unsure if the temp in the wood got high enough to kill the eggs of powder post beetles. I didn't experiment with turning the fans off during the day with the vents closed, but may next time to see if the temp gets high enough for long enough. Is that safe for the lumber (cracking, warping, etc.)?
Great to hear that your kiln is working. Pulling a load out of the kiln for the first time must be about as exciting as pulling your first log off the sawmill. As long as you have the kiln closed up so that it isn't removing moisture, you shouldn't have a problem going to bug killing temps. 135 deg F seems to be the accepted temperature, for an hour, plus 1 hr for each 1" thickness of wood. The warmer air holds more moisture, so there will still be some drying taking place. The safest procedure would be to shut it down in the morning after the wood has conditioned, and leave it shut down until the next morning. Adding one day to the kiln schedule to kill the bugs is a good deal.
Good judgement comes from experience... experience comes from bad judgement.
Oakie, I think the first log was more exciting. Taking boards out of the kiln is just work , though satisfying. Unlike cutting up a log, the boards don't look much different coming out than they did going in. I like your idea about the bug-killing; will do that next time. Should be plenty hot in July. Thanks for the compliments, Bill. I believe the lumber from trees you have in the northwest could go into a kiln immediately after cutting rather than air-drying first. Isn't that the way they do it there?
Eddie the mills around here stick it straight into the kiln and some of my customers take it straight to a company that has a large kiln that will put it through for $40 a thou. Once I get a kiln built I may try it both ways depending on the moisture content to start with.
I have had my kiln get close to 180 to 200 degrees with all the vents shut, that was when it got so hot it melted the plastic fan blades causing them to sag. But that temp is just a few degrees hotter than what it is in normally in Oklahoma outside in July. Mine with the fans and vents open is around 150 degrees.
I've been to Oklahoma and it gets hot, but not that hot --- not too much different than here in southwest Missouri. I put a 2' X 10' silver tarp across the bottom of the glass to be in accord with the recommendations of Virginia Tech (1:10 ratio of collector area to bd. ft. lumber). It probably would have gotten hotter without that --- should have removed it at the end I guess. I learn as I go.
Second Thoughts:
The spacing of studs and joists is not clearly stated in the V.T. plans. I suggest careful planning of floor joist spacing with board lengths in mind.
I put numerous screws along the roof edges to counter wind forces and seal the roof sides. All holes into Tuftex must be drilled oversize to allow expansion and contraction of the glazing and, even though I did that, I guess the edge screws were too close and too tight. There are now small cracks around those screws, but none over the main roof.
The massive doors weigh a lot and soon sagged to where they grate along the bottom threshold. I have to use a couple of hay hooks to grasp the door handles and pull with great force to open them. Always doable, but not ideal. I installed chains that hook to the doors from the front piers to hold the doors steady in the wind when open.
The black tarp I bought shrunk in width during the first kiln cycle, so its attachment points had to be redone - something to keep in mind.
When I start the kiln up with a load of air-dried oak, I open the vents only one or two inches. As the lumber approaches 6-8 percent moisture, I close the vents down to only about an 1/8".
That's all I can think of now. I'm storing some lumber in the kiln during this winter weather, but will probably not try another load until summer. I think I did four loads this last summer.
Nice work, Planning on building one. Eddie, hope you don't mind me asking, Whats the expenses looking like on this project? rough total? Seemed like when I looked at the plan, making the materials would just be more work. easyer to buy and get started.
My location would be remote, would have to be solar powered.
Hi, Sal. My total, including fans, electrical hook-up, timer, and tarp came to around $1900. But I already had the foundation poles, nails, some roofing screws, a ridge cap, purlin boards, and tin for the collector. There are probably a few corners I could have cut to lower the cost. For instance, I could have gone with 3/8" plywood all around instead of Smart Siding on the outside. Instead of the expensive Blackjack Rub'r Coat #57 I used to coat the inside, I could have just used roofing/foundation tar. Rather than 3/4" treated plywood for the floor, I might have used untreated, thinner stuff. Virginia Tech recommends ordinary box fans which are cheap and readily available. And anyone with a sawmill can cut their own lumber. I didn't however.
One thing I would add if I could do it over, and may still, is a small door on the side to insert, water, and remove seed flats in the late winter and early spring. It's not hot enough then to effectively dry lumber, but just right for starting plants. My front doors are too burdensome to be opening every day.
Another thing: I wouldn't use black weatherstripping directly under the glazing as I did along the edges - it apparently needs to reflect light there, not absorb it. The weatherstripping sold with Tuftex is white.
Thanks Eddie, My guess was 2000 so I was really close. My spot will be remote, So I will have to use an inverter and solar power... that site you guys posted is great. Thanks
Hi, it's fall 2014 now and there's nothing in the kiln. I did two or three loads this summer. It was not as hot as many previous summers and only got to 100 degrees a few days here in Missouri. I carefully measured temps every couple of hours during one kiln cycle and recorded thermometer temperatures at the back of the lumber pile on 95 degree days. With full glass exposure (no compensation for a less than a complete lumber load) and the fans running, I found temps up to 144 degrees at the peak of kiln heat (usually around 4 or 5pm). I have another thermometer placed higher on a side wall (on the back side of the tarp) which consistently registered 7 degrees higher than lumber-side temps. Temperatures on the sunny side of the tarp were not measured. The vents were opened only about 1/8" (near the end of the kiln cycle), so moisture at that time was probably lower than 8%. As the temps stayed above 135 degrees for several hours on these days, I feel confident that any bugs in the lumber were killed. A later load during cooler temperatures failed to rise above 130 degrees, so I may have reason to worry about that load.
One more thing: the Virginia Tech plan I used here is designed to safely dry hardwoods such as oak. There may be better (higher heat, more air flow?) designs for softwoods.
Good judgement comes from experience... experience comes from bad judgement.
Thanks, Bill, Oakie. That 8" on-center OSB paneling really complicates things if you want the seams to match and the edges to rest on studs. The first full kiln load will be some oak I cut last year, a mixture of red, white and black oak. I'm currently involved in a walnut cabinet project and would like to reduce its moisture content a tad, so that small bit of walnut may preceed the oak.
Ditto Eddiemac looks great. Thanks for the pics.
Cheers!
Steve
Here's the last pics. Got a mostly 8' load in and started it up last evening. To make the recommended proportion of collector area to load, I hung a 2' wide silver tarp under the glass across the bottom this morning.
The black tin on top of the lumber collects solar heat. The black baffle seen in the following photo also collects heat and directs blown air down over the collector panels. The air then flows down the opening in the front and back through the sticker spaces in the pile.
I put the vents on the inside of the kiln; maybe not the best idea, but I didn't want to get the ladder out every time I needed to adjust the upper openings.
There's 1/4" hardware cloth in the front of the vents to keep out birds and some insects.
I can see how it works. Thanks for posting, it's a real inspiration. Let us know how the first load turns out!
Good judgement comes from experience... experience comes from bad judgement.
This is only a suggestion from my past experience, I cut a 10x12 tarp in half and folded in to what ever size I needed to hang on each end of the wood pile in the kiln and weighted it down with a brick to more efficiently force the air through the stickers on the pile and did not loose air through the gap at the either end. You can just lay it over the collector and weight it down and then weight it down to the floor. It surprised me how much more it efficient quick the drying process was. Hope this helps. It took me 2 attempts on my own kilns to get it right and then several I built for others, yours looks like you have been building them for years, great job!
LM 2000, 15 HP, Trailer Package, setter, sharpener, Kubota M5700, Husky Chainsaws, Stihl 660 chainsaw, Woodmaster 718 4/1 planer (planer,sander,router and molder)
Thanks Oakie, Citrafarm. I stuck pieces of siding at the ends near the front to prevent air flow around the pile. Yours, however, may be a better way - more flexible. Anyone got any guidelines on what and when as pertains to the vents?
Eddiemac, looks awesome . You do great work! One day I hope to build one so thanks for all the pics.
Cheers!
Steve
You've certainly done a very nice thorough job building your kiln thank you for taking the time for pics. and explanations.
Bill
Well, it's been 7 days since I put in the load @12-14% moisture content (oak previously air-dried from last year). I'm too lazy to follow the correct procedure of cutting sample pieces and weighing them every day, so I'm using a moisture meter. My testing now indicates 6-8% (oops: forgot to adjust for temperature; will have to do that). I hope that's not drying too fast, but I don't see any sign of cracking or checking. The vents are almost closed now and the kiln temperature yesterday was 130 degrees at 4:00 pm.
I never used the weighing method either, I am lazier than you. I used a moisture meter also. Your drying time seems about right, I put green white oak in once at about 35% moisture and in 30 days it was about 6 to 8% but since I did not air dry it, it cracked and checkered. I began air drying for about 6 six months in the Oklahoma heat, then put it in the kiln at about 14 to 18 % moisture and got it down to 6 or 8 % with fantastic quality. It took about 2 weeks to get it to 6 to 8% so yours sounds good. It is better to dry slowly let the wood condition itself by absorbing humidity and drying slowly thus cutting down on cracks, warping and checkering. You will learn how to measure the time in the kiln based on your weather and humidity in your location. Good Luck
LM 2000, 15 HP, Trailer Package, setter, sharpener, Kubota M5700, Husky Chainsaws, Stihl 660 chainsaw, Woodmaster 718 4/1 planer (planer,sander,router and molder)
Drying too fast is also said to cause "case hardening" - from a book I read one time. Leaves residual stresses that may not be apparent until you thickness plane, at which time new warp and curl problems arise. I'll be interested to see if this happens in our lumber, but first we have to get back to working on the kiln. Work pressures for both of us have left us with precious little discretionary time recently. Frame is up, structure is awaiting black paint on appropriate surfaces, glazing, and roofing of the back slope.
I believe we are talking about the same thing, drying slowly allows the wood to "condition" which is to dry and absorb the humidity at night and repeat the process over and over slowly so it does not curl or crack, the same is true with concrete, that is why you have to keep it moist while drying. Anyway a old time "sawer" told me that solar kiln is 10 times better that electrical heat because it forces you to take it slower. Commercial kiln lumber has a far greater loss in quality board feet but has 100 times the production because of speed.
LM 2000, 15 HP, Trailer Package, setter, sharpener, Kubota M5700, Husky Chainsaws, Stihl 660 chainsaw, Woodmaster 718 4/1 planer (planer,sander,router and molder)
citrafarm
I expect we are, I just threw in the descriptor in case it rang a bell. I also expect you are right, commercial (or even agressive hobby) drying is all about shortening the cycle. If you don't extract at extreme rates, it would seem less likely to do harm. I have a pile of 15% lumber, but I also have quite a pile of soon-to-be-fresh-cut lumber. I could throw the greenest wood in the kiln first, to dry it quickly, but I suspect that won't be satisfactory. I'll more likely dry the fresh stuff for a year in the air, then kiln it when my pal wants to use it. Big problem will be getting him to predict his needs far enough in advance to allow kiln drying off-season.
Gene Wengert, kiln drying expert, says "casehardening, also called drying stress and tension set, develops very early in drying." Therefore, I'm crossing my fingers that it won't happen to the previously air-dried lumber I'm practicing on in my new kiln. Only time will tell. Even though I started this thread, it is open to anyone who wants to post pictures of their solar kilns --- hint, hint.
My load of oak dried to 6% moisture content from an initial 12-14% in 11 days. I removed it from the kiln this morning and found no evidence of degrade. I'm convinced this design provides a safe means to quickly and cheaply dry lumber. Killing bugs, I don't know. The highest temperature I recorded was 134 degrees behind the lumber stack at the back of the kiln (inside), so I'm unsure if the temp in the wood got high enough to kill the eggs of powder post beetles. I didn't experiment with turning the fans off during the day with the vents closed, but may next time to see if the temp gets high enough for long enough. Is that safe for the lumber (cracking, warping, etc.)?
TY for keeping us posted Eddie sure happy for you the wood came out nice after the great job you did on the kiln.
Bill
Great to hear that your kiln is working. Pulling a load out of the kiln for the first time must be about as exciting as pulling your first log off the sawmill. As long as you have the kiln closed up so that it isn't removing moisture, you shouldn't have a problem going to bug killing temps. 135 deg F seems to be the accepted temperature, for an hour, plus 1 hr for each 1" thickness of wood. The warmer air holds more moisture, so there will still be some drying taking place. The safest procedure would be to shut it down in the morning after the wood has conditioned, and leave it shut down until the next morning. Adding one day to the kiln schedule to kill the bugs is a good deal.
Good judgement comes from experience... experience comes from bad judgement.
Oakie, I think the first log was more exciting. Taking boards out of the kiln is just work , though satisfying. Unlike cutting up a log, the boards don't look much different coming out than they did going in. I like your idea about the bug-killing; will do that next time. Should be plenty hot in July. Thanks for the compliments, Bill. I believe the lumber from trees you have in the northwest could go into a kiln immediately after cutting rather than air-drying first. Isn't that the way they do it there?
Eddie the mills around here stick it straight into the kiln and some of my customers take it straight to a company that has a large kiln that will put it through for $40 a thou. Once I get a kiln built I may try it both ways depending on the moisture content to start with.
Bill
I have had my kiln get close to 180 to 200 degrees with all the vents shut, that was when it got so hot it melted the plastic fan blades causing them to sag. But that temp is just a few degrees hotter than what it is in normally in Oklahoma outside in July. Mine with the fans and vents open is around 150 degrees.
LM 2000, 15 HP, Trailer Package, setter, sharpener, Kubota M5700, Husky Chainsaws, Stihl 660 chainsaw, Woodmaster 718 4/1 planer (planer,sander,router and molder)
I've been to Oklahoma and it gets hot, but not that hot --- not too much different than here in southwest Missouri. I put a 2' X 10' silver tarp across the bottom of the glass to be in accord with the recommendations of Virginia Tech (1:10 ratio of collector area to bd. ft. lumber). It probably would have gotten hotter without that --- should have removed it at the end I guess. I learn as I go.
Second Thoughts:
The spacing of studs and joists is not clearly stated in the V.T. plans. I suggest careful planning of floor joist spacing with board lengths in mind.
I put numerous screws along the roof edges to counter wind forces and seal the roof sides. All holes into Tuftex must be drilled oversize to allow expansion and contraction of the glazing and, even though I did that, I guess the edge screws were too close and too tight. There are now small cracks around those screws, but none over the main roof.
The massive doors weigh a lot and soon sagged to where they grate along the bottom threshold. I have to use a couple of hay hooks to grasp the door handles and pull with great force to open them. Always doable, but not ideal. I installed chains that hook to the doors from the front piers to hold the doors steady in the wind when open.
The black tarp I bought shrunk in width during the first kiln cycle, so its attachment points had to be redone - something to keep in mind.
When I start the kiln up with a load of air-dried oak, I open the vents only one or two inches. As the lumber approaches 6-8 percent moisture, I close the vents down to only about an 1/8".
That's all I can think of now. I'm storing some lumber in the kiln during this winter weather, but will probably not try another load until summer. I think I did four loads this last summer.
Nice work, Planning on building one. Eddie, hope you don't mind me asking, Whats the expenses looking like on this project? rough total? Seemed like when I looked at the plan, making the materials would just be more work. easyer to buy and get started.
My location would be remote, would have to be solar powered.
Hi, Sal. My total, including fans, electrical hook-up, timer, and tarp came to around $1900. But I already had the foundation poles, nails, some roofing screws, a ridge cap, purlin boards, and tin for the collector. There are probably a few corners I could have cut to lower the cost. For instance, I could have gone with 3/8" plywood all around instead of Smart Siding on the outside. Instead of the expensive Blackjack Rub'r Coat #57 I used to coat the inside, I could have just used roofing/foundation tar. Rather than 3/4" treated plywood for the floor, I might have used untreated, thinner stuff. Virginia Tech recommends ordinary box fans which are cheap and readily available. And anyone with a sawmill can cut their own lumber. I didn't however.
duplicate post, sorry.
One thing I would add if I could do it over, and may still, is a small door on the side to insert, water, and remove seed flats in the late winter and early spring. It's not hot enough then to effectively dry lumber, but just right for starting plants. My front doors are too burdensome to be opening every day.
Another thing: I wouldn't use black weatherstripping directly under the glazing as I did along the edges - it apparently needs to reflect light there, not absorb it. The weatherstripping sold with Tuftex is white.
Now I feel stupid!
Thanks Eddie, My guess was 2000 so I was really close. My spot will be remote, So I will have to use an inverter and solar power... that site you guys posted is great. Thanks
Hi, it's fall 2014 now and there's nothing in the kiln. I did two or three loads this summer. It was not as hot as many previous summers and only got to 100 degrees a few days here in Missouri. I carefully measured temps every couple of hours during one kiln cycle and recorded thermometer temperatures at the back of the lumber pile on 95 degree days. With full glass exposure (no compensation for a less than a complete lumber load) and the fans running, I found temps up to 144 degrees at the peak of kiln heat (usually around 4 or 5pm). I have another thermometer placed higher on a side wall (on the back side of the tarp) which consistently registered 7 degrees higher than lumber-side temps. Temperatures on the sunny side of the tarp were not measured. The vents were opened only about 1/8" (near the end of the kiln cycle), so moisture at that time was probably lower than 8%. As the temps stayed above 135 degrees for several hours on these days, I feel confident that any bugs in the lumber were killed. A later load during cooler temperatures failed to rise above 130 degrees, so I may have reason to worry about that load.
One more thing: the Virginia Tech plan I used here is designed to safely dry hardwoods such as oak. There may be better (higher heat, more air flow?) designs for softwoods.
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