Drying Wood, Or Home Made Wood Kilns?

[Quarter]

I was wondering if any have built their own small scale wood kiln.

I've got a 8/4 piece of cocobolo that I'd like to accelerate the drying on, its down around 15% - 16% right now.

Web searches come up with a lot of interesting kiln ideas, solar, dehumidification, and vacuum systems, but all are fairly large scale.

I had the thought of maybe just building a suitable sized air tight chamber, or maybe a vac bag, and using a vacuum pump or venturi to accelerate the drying a bit.

It doesn't need to be super fast, just that I'd rather not wait another year or more to use it

Any other ideas for a simple and easy solution for small quantitys?

[John Abbett]

There are lots of ways to do it. For one board it might be tough. Part of the drying process causes the boards to warp. The kilns stack the boards in piles with stickers between the layers to let air flow. They put weight on top. It keeps everything flat. Be cautious, you might end up with warping or checking.

Dry air will do it, or heat and good air air flow.

I am building a 10x20 ft solar kiln out of a greenhouse. It will get plenty hot, even in the winter it will be warm.

Do some google searches, plenty of info out there.

-John

[zyonsdream]

you dont want air tight. Drying evaporates liquid from the wood which causes humidity in the air. You need a way for the moisture to get out. I've seen a lot of set ups where people use brick and make a small "dog house" like enclosure with a door. A couple of 100W light bulbs and you are in business.

[orgmorg]

A small box with a dehumidifier will work just fine for what you are doing.

Most dehumidifiers have an attachment for a hose so you don't have to keep emptying the bucket, this will take care of getting rid of the water, so you can make it fairly air tight. They have a fan, as well, so that will help with air circulation.

15-16% is a good point to start this process.

An old air conditioner will work as well, just don't vent the hot air, like you normally would to cool a room, keep the whole thing enclosed.

Either way, don't crank it full bore at first, start off slow, and see how it goes. you can always turn it up later if it is going too slow, but you don't want to stress the wood by removing moisture too fast and/or heating it up too much.

A dehumidifier or AC will kick out quite a bit of heat, in fact it may even shut down if it gets too hot. You will probably want to provide a means of venting excess heat.

I've dried quite a bit of wood this way, but all domestic stuff.

I'm sure Fryovanni will be along in a bit, he has more experience with exotics like cocobolo.

But don't bother messing with vacuum drying. It really requires a pretty heavy duty chamber, and much more technical setup.

Edited August 19, 2008 by orgmorg

[Quarter]

Thanks all for the input, it is much appreciated.

A quick Google turns up some small inexpensive dehumidifiers that would be a great size for a closet or other small area.

Slow going is fine for me. This piece has been air drying for almost 2 years, but at the rate its going, I just don't want to wait another year

[fryovanni]

Cocobolo does dry VERY slow, it is a pain(too bad it is such a great sounding wood, otherwise I would never deal with it). I would be careful with heat(very high heat that is) because you really don't want to case harden the Cocobolo, cause then you are going to be really frustrated. Your getting down to a low enough moisture content where accelerating the drying is less risky. I usually see the most nasty drying damage between 16-24ish percent(when the tension and pressure switches), after your down below 14% drying damage is very mild usually(case hardening not withstanding).

The first thing I would consider is, do you need that 2" thickness? If you are using it for a top, or acoustic parts bringing the dimension down a bit will really accelerate the drying( I am sure you already know that though).

If you use an aggresive method(say the "solar kiln" idea). Limiting the volume of air will act to control the amount and rate you remove the moisture. The garbage bag in the sun for a bit, then open and turn the bag inside out and repeat(solar kiln thing), has the limited volume of air acting as a safety check on rate. Other methods mentioned, controlling the balance between temp, moisture level, and air flow or volume of air are all going to dictate the rate of drying. I personally like to use mild temp, mild humidity and lots of air. Increasing the temp a little along with air flow and mild humidity(moving the wood indoors) is usually the next step for me. I have a small dehumidifyer, that will pull down the extra moisture in the air if I am drying a lot of wood. About the only time I really jack up the heat is when I overdry wood, and I only do that on wood that is down to 8 percent or less. I have a box that has heating elements, and fans that I can cycle. I use that only on soundboards(cycle them down, then bake them) which is not something I would ever do with solid body wood).

Rich

[Quarter]

Thanks Rich ... good food for thought

[zyonsdream]

Also keep in mind the cost of drying it yourself and the cost of having it dried. I have a guy here who will do it for 33 cents a BF and when you factor in the cost of running a dehumidifier or any other heating source with today's energy costs it seems more cost effective to just have it done.

For example, if I run my air conditioner 24/7 for a month it's going to raise my electric bill about $50.00 (believe me; I know...I get the bill) so let's say you can adequately dry the wood you want in 2 months. That's $100.00 to dry the wood (not including what it cost to build the chamber.) For that money, I could have paid to have 303 BF of lumber dried and I'd get it in less time. Even if you dedicate a closet in your home to a kiln I highly doubt you could dry 303 BF of lumber in 2 months (without cracking the hell out of it.)

Most cabinet makers can help you find someone in your area that dries wood or even look up some smaller lumber mills.

Just my 33cent

[fryovanni]

Also keep in mind the cost of drying it yourself and the cost of having it dried. I have a guy here who will do it for 33 cents a BF and when you factor in the cost of running a dehumidifier or any other heating source with today's energy costs it seems more cost effective to just have it done.

For example, if I run my air conditioner 24/7 for a month it's going to raise my electric bill about $50.00 (believe me; I know...I get the bill) so let's say you can adequately dry the wood you want in 2 months. That's $100.00 to dry the wood (not including what it cost to build the chamber.) For that money, I could have paid to have 303 BF of lumber dried and I'd get it in less time. Even if you dedicate a closet in your home to a kiln I highly doubt you could dry 303 BF of lumber in 2 months (without cracking the hell out of it.)

Most cabinet makers can help you find someone in your area that dries wood or even look up some smaller lumber mills.

Just my 33cent

Very sensable idea, but I am not sure if it would apply to this small bit of pretty much dry wood. It would be very sensable if a person had just milled up a log, and wanted to speed up the process. I would also wonder what wood would be in the kiln at the time(obviously they won't dry this amount of wood by itself), would they mix a wood like Cocobolo in with any other woods that are going to be dried? Seems like drying schedules could be pretty varied, and using an overly aggressive schedule would increase the rate of damage, using a slower schedule is going to waste kiln time.

Your comments make good sense with the cost of energy rising, and a person should really consider that and how they are drying wood. If you have space that is already conditioned and have time available, it can make good use of the space with little difference in cost. If you have to dedicate and micro control or force accelerated drying then you really need to look over the costs to value. I personally limit 95% of my drying to existing available controlled space(or use uncontrolled for early drying). If I am going to crank up fans, and use forced air to speed things up a bit, I make sure I have a fair amount of wood making use of that effort. If I use raise the temp, drop the humidity, and move the air I make sure it is really needed, because it does cost a lot.

Drying and aclimating costs really make strong case for allowing yourself a good deal of time(meaning have a stock of ready wood) so you can have wood ready to use while you allow a back stock plenty of time to get ready for use.

Rich

[zyonsdream]

Also keep in mind the cost of drying it yourself and the cost of having it dried. I have a guy here who will do it for 33 cents a BF and when you factor in the cost of running a dehumidifier or any other heating source with today's energy costs it seems more cost effective to just have it done.

For example, if I run my air conditioner 24/7 for a month it's going to raise my electric bill about $50.00 (believe me; I know...I get the bill) so let's say you can adequately dry the wood you want in 2 months. That's $100.00 to dry the wood (not including what it cost to build the chamber.) For that money, I could have paid to have 303 BF of lumber dried and I'd get it in less time. Even if you dedicate a closet in your home to a kiln I highly doubt you could dry 303 BF of lumber in 2 months (without cracking the hell out of it.)

Most cabinet makers can help you find someone in your area that dries wood or even look up some smaller lumber mills.

Just my 33cent

Very sensable idea, but I am not sure if it would apply to this small bit of pretty much dry wood. It would be very sensable if a person had just milled up a log, and wanted to speed up the process. I would also wonder what wood would be in the kiln at the time(obviously they won't dry this amount of wood by itself), would they mix a wood like Cocobolo in with any other woods that are going to be dried? Seems like drying schedules could be pretty varied, and using an overly aggressive schedule would increase the rate of damage, using a slower schedule is going to waste kiln time.

Your comments make good sense with the cost of energy rising, and a person should really consider that and how they are drying wood. If you have space that is already conditioned and have time available, it can make good use of the space with little difference in cost. If you have to dedicate and micro control or force accelerated drying then you really need to look over the costs to value. I personally limit 95% of my drying to existing available controlled space(or use uncontrolled for early drying). If I am going to crank up fans, and use forced air to speed things up a bit, I make sure I have a fair amount of wood making use of that effort. If I use raise the temp, drop the humidity, and move the air I make sure it is really needed, because it does cost a lot.

Drying and aclimating costs really make strong case for allowing yourself a good deal of time(meaning have a stock of ready wood) so you can have wood ready to use while you allow a back stock plenty of time to get ready for use.

Rich

Good points! It really comes down to how affective you can be at it. I've thought about building my own and even planned one out but I get most of my wood dried and rarely do I have anything I need to have dried. The only reason I know about the local guy with will do it is because my neighbor chopped down a perfectly good maple tree and I wanted it. I'm going to be looking into all of this bit more as my grandpa has a few black walnut trees that will be coming down soon and I would hate to see any of it not end up in my shop!

If anything, building your own kiln is a great learning experience on how drying wood affects it's stability.

[Quarter]

Thanks zyonsdream ... great suggestions and good grounded advice.

... Drying and aclimating costs really make strong case for allowing yourself a good deal of time(meaning have a stock of ready wood) so you can have wood ready to use while you allow a back stock plenty of time to get ready for use.

Absolutely, I couldn't agree more. I normally buy dry wood and rack it up for future use, but once in a while I come across a piece I like that is not dry. Usually I'll pass, but have increasingly been considering drying my own.

In a perfect world, I could run it through a kiln, then rack it up for future use. Problem is that its hard to justify building a kiln for just the odd piece here and there.

I'm going to explore the topic some more and may try my hand at building a smaller scale kiln. For a one off piece, its not a good investment, but as a learning tool and possible future use, it has merits.

Right now, a solar type seems the most economically sensible, but the vacuum types appeal to me due to the lower temps needed.

[cherokee6]

As stated above go solar. Using a dehumidier or other method is too costly. There was a solar kiln designed in Fine Woodworking a number of years ago you could probably look up at the library. It had a fan built in for air circulation and was built to hold quite a bit of wood. It was probably 8ft x 10ft. The article also discussed how to stack the wood, etc. It was slower than a regular kiln but you ended up with less checking, etc. I don't recall the details. You may have to go back 15 years ago.

[Nicko_Lps]

All the ideas above are respectable,but then again an air-dryied wood is much better...

When you force wood to dry fast some of the fluids contained are vapored but some crystalise and stay inside,that cause the wood to be heavyer not that stable comparing to air-dryed and if you use water-alcohol dyes directly to the wood it could not stain some pores of the wood that are filled with the crystalised tree juice whatever its called,it happens to happen rarely,but its a bit more expectable with to happen with ash.

A hard wood as cocolobo will dry a lot slower than others,as fryovanni said.

But then again it takes looong,cant be sure how much but 4 years at least are disirable(air-drying),if you can leave it and find something else it would be better for you since that project youre gonna built is not a chair...

You can do as you wish,but i would not even think to start a guitar project with a wood piece that im not so sure if its dryed or not.It could be a total disaster if wood is not dryed well or dryed correctly,they have ways to do that im not aware of..

Peace

[fryovanni]

There are different issues to deal with when drying wood, and a lot of the issues deal with the state the wood is at in the drying process. Any kiln you put together has to be able to adjust for these issues to regulate your rate and risks. Remember wood has to wick the water out from the core, and that is the trick. When wood is green, it has a high moisture content. The shell will obviously release moisture faster than the deeper moisture in the core. You need to allow that moisture to wick its way to the outer shell so it can release. If you block that ability for water to wick to the surface you trap the moisture(case hardening). Keep in mind drying damage also relates to this uneven rate of drying. As the wood releases moisture it shrinks, this means the shell will shrink and the core that has not been able to release its moisture will not. This gives you a picture of what is happening to the pressures in the wood initially. As this process goes along, and given the core moisture is able to continue to wick at a fair rate the core will start to lose moisture and shrink. If the outer shell has become rigid from becoming extra dry it will hold firm(kinda like a ring around the shrinking core). This is where you go from shell damage to core or heart damage. From my experience it seems like this transition generally starts in the upper to mid twenty percent moisture range, and settles in the mid teens or there abouts.

So consider this generic picture of what is happening when you decide on how you want to speed the process. It is all about finding the spot where moisture is allowed to wick quickly and not do too much damage by building to much stress. The greater(to a point) the difference in dryiness you have between the shell and core, the faster the core moisture will wick to the shell and release. The greater the difference the higher the difference in shrinkage(core to shell) and thus the more damage you will see.

This is why you will often see logs allowed to air dry for a spell(get some of the initial drying out of the way as gently as possible). Then milling to ruff dimension(allowing for shrinkage, damage, and distortion). Early in the kiln the process is mild, to limit the stress and in so limit damage. When the wood has become fairly dry, the schedules become more aggressive, because the volume of water being wrung out so to speak is smaller(smaller shrinkage=less potential for stress). They can get very aggressive at times(when the wood has become very dry) forcing the wood to an overdry state, and then condition it back up to closer to equilibrium(at the very peak of heating during these overdrying schedules, you may even crystalize or set the pitch).

The schedules for drying vary, because you are looking for a sweet spot(damage to rate the wood can release moisture). Drying Cocobolo on a schedule for certain softwoods is likely to lead to high damage rates. Getting aggressive with Cocobolo too early can lead to case hardening which will halt the drying. These schedules are a bit of an art(knowing your kiln, the wood, your climate, and where the wood is at(in the drying when you recieve it). You should be able to look up schedules that people have used, and recommendations for many commercial woods(exotics may be more hit and miss), based on the kiln set up they use.

Personally, I would and do defer to a slower less agressive rate if I am not sure( I am not about to risk my high dollar or hard to impossible to replace woods, because I am in a hurry). You will make the process less damaging and minimise risk. Remember, some woods will have high drying damage even when mild air drying is used. A lot of the learning is going to be school of hard knocks, and will cost you $$$ in drying damage. Just remember not to blame the wood when you push it too hard and get heavy losses.

Also; Regarding the solar kiln(plastic bag). The concept is good and works fine. The beauty is that it regulates itself. If you add air flow you lose the regulation, by allowing for more transfer, you add more air volume you increase the amount of moisture pulled from the shell during a cycle(more stress). With a method like this, you are able to use heat to assist in drawing moisture, but in cycles that limit the imbablance. Low cost, straight forward, self regulating, elegant for the small volume of wood. The one caution would be to be careful with light colored wood and warm moisture in a sealed bag. This can lead to mold and discoloration. You have to stay on top of the process, of course at any time you can just pull it out of the bag and go back to air drying(kind of cycle at will).

Rich