Kiln for thick slabs

[Seaman]

Sorry if this has been covered, I have looked and can't find specific answers.

I cut slabs with a Lucas. Maple, cherry, walnut, some oak. Some are green, but Most logs have been down for several years, lying on the ground. I cut 2 to 4 in slabs, over 24 in wide.
Is there anything I should do different than drying lumber?

My idea is to build a 18 x 7 foot solar kiln, then in cooler months seal it up and use a dehumidifier. I am following the bug killing thread with interest, seems like it would be easier to kill bugs with chemicals than heat.

I need advice from others who have dried slabs of this size.
Thanks

Frank

[Jay C. White Cloud]

seal and cleat ends supper quick, dry slowly, yes to chemical bug kill.  slower is better with slabs or work them "green" with the correct methods.

Regards,

jay

[GeneWengert-WoodDoc]

The problem with bug killing with chemicals for 4" slabs is that it will take forever for the chemical to get in deeply.  Heat is faster and cheaper, but heat only sanitizes at that mmoment, while chemicals may provide longer protection.  Chemicals may be in the planer chips and sawdust, which can be an issue for some people; heat would not be an issue for subsequent processing.  I have not seen any studies on the effects of chemicals like the borax related products and the effect on glue bond strength or finishing...what finishes have not issues and what finishes have an issue.

Note that the Borax related preservatives are in water, so you would be rewetting the lumber if you used that treatment.  Rewetting for some woods is not suggested due to checking and color issues.

In your case, the fact that the logs have been down for a while means that insects issues are indeed likely, so your concerns are indeed noteworthy and reflect your interest in providing a high quality product.  You should point this out to your potential customers, as not all mills have that concern or treatment.

[Seaman]

Thank you Gentlemen,
I have sent e-mails to the Borax folks so hope to talk to one of their SMEs.

Would a DH kiln be gentler on the slabs? I was looking at solar, but would like to be able to dry year round.

Doc, when you say the chemicals take "forever" to penetrate, how long, and is it several applications? Could this be done as they air dried, or will I have to pull them out of the kiln to treat?
Thank you all for the knowledge you are willing to share on this forum!
Frank

[Seaman]

UPON FURTHER REVIEW....

Seems to me... If you treat slabs with chemicals, the outer layer will be affected first, keeping out new bugs, and killing those that hatch and work their way out. So that at the end of the drying process, the wood would be safe.

This coming of course from one whom has never dried or treated wood before!

I will bow before the opinions of the wise.

[Jay C. White Cloud]

Hi Frank,

Seems to me... If you treat slabs with chemicals, the outer layer will be affected first, keeping out new bugs, and killing those that hatch and work their way out. So that at the end of the drying process, the wood would be safe.

Yes, and depending on the product, it can be very effective.

Would a DH kiln be gentler on the slabs?

Yes, much gentler.  We work in green wood almost exclusively, and/or just air dried.  A gentle dehumidifying kiln would probably be fine for slabs, accelerating the drying process but not case hardening or focusing any stresses that may be in the slab.

Doc, when you say the chemicals take "forever" to penetrate, how long, and is it several applications?

It depends on the type used, but surface application, early, is usually more than enough to dissuade nesting female wood loving Coleoptera, unless they are already in the wood.  Doc is correct about heat being the only real effective way of killing present larva, as far as I know.  DDT and Dursban, among others could, but I won't work with those anymore, they are just too toxic.

Could this be done as they air dried, or will I have to pull them out of the kiln to treat?

Pyrethroids could gas your kiln and kill everything but is an organic based on chrysanthemums and breaks down quickly, having no really long lasting effect.

Hope that helps, let us know what else you learn?

Regards,

jay

[GeneWengert-WoodDoc]

If the chemicals diffuse slowly into the wood, any insects inside the lumber can do considerable damage before they come out.  This needs to be considered.

Wood dries based on the temperature, RH and air flow.   A DH kiln represents hardware differences, but it still operates by passing air of a given temperature RH and velocity across the lumber.  Many DH kilns operate at the same temperature as a hot water or steam kiln.  Some DH kilns can operate at cooler temrpeatures.  Some Steam kilns operate at higher temperatures.  So, a DH kiln and a steam or hot water kiln can all dry lumber with high quality if operated at the same temperature, RH and air flow.  If somopen operating one of these pieces of hardware has a "magic" schedule, then it likely that the others could duplicate the conditions.  I recall that someone once advertised that their vent controls on a steam kiln resulted in half as long of drying time.  Vents are not part of the equation, so if a new vent thingamajig makes wood dry faster, it is because the RH is lower, temperature is higher oand or velocity is higher.  And, if we knew these new conditions, we could create the same  in any kiln (assuming the kiln has enough power, etc.).

As mentioned, DH has the ability to operate at cooler temperatures than steam, but it does not have to stay cooler.  There are a few cases where cooler (under 100 F) can improve quality, but not with 8/4 and under North American species.  So when considering a kiln, make your decision based on items such as cost (capital and operating), and whether you want a boiler (steam or hot water), have electrical power, and so on.  If you are under 1 to 2 million BF annual, you will find that DH will often come out on top.

Note that probably any kiln can be operated improperly and give poor quality.  This reflects the operators skill and not the hardware basics.

Hope this perspective gives you guidance and also affirms the direction you are considering.

One last thought...always plan where you might put a second kiln...many operations that start in drying find that business is good enough that they need another kiln.  Hopefully the first kiln is located in an optimum spot.

Havng said all this, note that I ignored vacuum kilns, such as Den has.  I do not know what annual volume you need to make them profitable.

Also, if for example you think that you might also dry some 10/4 basswood squares or other special items, consider farming out the drying for these specialty products rather than designing your equipment to dry all thicknesses and all species (expensive to do).

Anything I said that does not make sense?

[Jay C. White Cloud]

Gene, that was awesome! I have learned so much from you about the "true" realities of kilning and you confirmed many of my thoughts about it.  It is an art on to itself. and in the hands of a capable person, it sound invaluable for commercial or semi-commercial applications in drying wood.  If I was ever to produce a kiln for drying wood, at any production rate, I would look to you for guidance.  I have always thought that a steam kiln could both dry and relax wood at the same time, there by relieving stress and avoiding some of the issues like case hardening, even in timber frames size stock.  We have even thought about using a steam kiln for foreign vintage frames, like Japanese Minka farm houses, for rendering them pest free for domestic use, there by avoiding the chemical treatment method.  We just aren't sure that it would be cost effective or have the residual effective of a pest control treatment modality.

Regards,

jay

[GeneWengert-WoodDoc]

Jay C. White Cloud...and others

Thanks for your kind words.  If you do indeed want to make real money--lots of money--then you will want a kiln or two.  Sell the sawmill!

Drying stresses are a normal part of drying because the outside dries first before the core.  The key is to control those stresses so that the lumber stays flat (Stresses can help keeping lumber flat so we often do not want to remove them too early in drying.) and so that the stress does not exceed the strength of the wood.  The idea of using steam to relieve stresses during the cycle instead of at the end has been proposed and was tried by John Divine about 50 years ago.  I would say that if it worked and was beneficial, we would see it being done today.

Actually, we do see stress relief being done during the cycle in a solar kiln, as each evening the RH in the kiln reaches 100% which does relieve the stress that developed during the day.  We also see a similar effect with air dried lumber.  That is, after solar drying, the wood will usually have no residual drying stress (casehardening is another term for this stress).  Air dried lumber will have a lot less stress than lumber kiln dried green from the saw.  (This reduced stress in air dried is often why someone claims that they can relieve stress easily in a kiln with their new, fancy stress relief system or procedure...there was minimal stress to begin with.)

[Jay C. White Cloud]

Morn'n Gene,

Air dried lumber will have a lot less stress than lumber kiln dried green from the saw.  (This reduced stress in air dried is often why someone claims that they can relieve stress easily in a kiln with their new, fancy stress relief system or procedure...there was minimal stress to begin with.)

This statement, put this way, is what I have been saying for years, (but not so few words. :D)  Thank's again.

We have toyed with the idea of a large solar kiln for a few years now, or maybe just a large drying barn?  We have slabs to store, and not everything can or will be worked green, (well by me green, but we do have other work that needs dry... ;D)  What are the largest solar kilns you know of?

[Ianab]

In Australia they build big commercial solar kilns. Lots of sun and difficult to dry species makes it viable. This page shows a pair of kilns holding 100 m³ (~40,000 bd/ft) each
http://www.solardry.com.au/solardry/solar-timber-kiln-100m.htm

As Gene says, it's about temp, RH and air flow. The kiln can be scaled up or down, as long as you keep the conditions similar, the wood will dry the same.

Ian

[red oaks lumber]

the best money i make is drying lumber, it makes money without you needing to be there 24/7.

[GeneWengert-WoodDoc]

In VT, there would be six months or more with little sunlight, so solar would be limited production much of the year.

I think an open shed is probably good for initial drying followed by an appropriate kiln.

I would argue that a large solar kiln is too expensive per BF of lumber produced.  The structure is in the same price as a conventional kiln, labor is the same, and drying would be slower than in conventional.  So, spend a few more dollars to get a 24/7 system.  Do you want to bet your money on sunshine?

Lest anyone thinks I am against solar kilns, I wrote my Masters Thesis on them, played with them starting 1961, and developed the Virginia Tech design in 1978.  There is a place for them, but not every place.

[Ianab]

That's why I mentioned those big solar units where in Aussie with MUCH more sunshine. I bet they would have good sun 90% of the year. But for a commercial enterprise have a six month "off season" would be a big problem.

I can see for Jay's application even a smaller solar kiln could work to finish off air dried pieces. If it was only to get them from ~15% air dried to ~8% kiln dried it would probably only take a week in a solar kiln?

Then just a big pole barn for air drying.

Ian

[Jay C. White Cloud]

Thank's Ian, and Gene,

We are discussing both, but leaning toward Genes approach in a way.  Big drying and storage shed, with roof solar gain through clear roof, then a bio fuel, pellet furnace for the kiln, if money comes in, maybe even a steam unit, I'm just thinking, if I put the kiln(s) in the end of the green house, I can get a lot of bang for my buck with excess heat and humidity.  This is several years away, but I like to really plan and examine design principles, not to mention this might be part of the votech for your local high school as well.

Thank's again,

jay

[Biocmp]

I would start a new topic but this is packed full of information.

If someone were looking to build a kiln for flooring, furniture slabs and timberframe components, and they lived outside of St. Louis, MO, is a solar kiln a viable option?

This wouldn't need to run any sort of commercial turnover, but enough to be profitable on a part time basis and give me enough wood for my projects.

I know this has to come off as a very uneducated question because it could likely be answered in a number of ways but I'd like to hear from the forum experts. I'm just beginning this process and I want to have a working plan.

Thanks

[GeneWengert-WoodDoc]

From a technical viewpoint, certainly solar would be reasonable in St. Louis, probably 8 months of the year.  I am not sure however, if it would be highly profitable, as you may get only 3 to 4 loads of lumber through in a year.  That is maybe 6000 BF and your profit would be fairly small.  I do believe that a small DH or hot water kiln that produced 12 months a year would be better, along with an air yard (maybe an open shed) to pre dry the lumber before it goes into the kiln.  With an air yard and a 1000 BF kiln, you could get 26-30 loads a year through the kiln, which, even after expenses, would have maybe 8 times more profit at the end of the year.  (All this is wrt 4/4 and 5/4.)

[vfauto]

In VT, there would be six months or more with little sunlight, so solar would be limited production much of the year.

I think an open shed is probably good for initial drying followed by an appropriate kiln.

I would argue that a large solar kiln is too expensive per BF of lumber produced.  The structure is in the same price as a conventional kiln, labor is the same, and drying would be slower than in conventional.  So, spend a few more dollars to get a 24/7 system.  Do you want to bet your money on sunshine?

Lest anyone thinks I am against solar kilns, I wrote my Masters Thesis on them, played with them starting 1961, and developed the Virginia Tech design in 1978.  There is a place for them, but not every place.

If not every place then where would they be good, I live in Massachusetts.

[Ianab]

Places with more sun.

They use some large solar kilns commercially in Australia, where there is plenty of sun, pretty much all year round, and the Eucalyptus needs to be dried slower anyway. So the slower schedule of the solar kiln isn't so much of a problem.

For a "hobby" setup, where you aren't under such time constraints (it doesn't matter if it takes 2 months to get wood dry, or 4 months in winter) then it's a good option. The set up and running costs are less, so it's easier to justify.

Like Gene says, the kiln will work in a less than ideal climate for most of the year, and any wood in there in winter will at least be safe and dry slowly. But not so good when you have customers and the bank manager waiting for the load to finish.

Ian

[BtownCutter]

I built a solar kiln last summer.  It holds about a thousand board feet.  I'm a few hours due east of St. Louis.  I'll let you know how it goes.

[WDH]

Post some pics.