Kiln dried, air dried, MCs and EMCs

[GeneWengert-WoodDoc]

I suggest that we do not use the term "kiln dried" or "air dried" when referring to hardwood lumber, as there is no traditional or legal definition associated with those expressions. There are many kilns running at a maximum of 115 F.  They do not kill insects.  There are many that have lumber over 10% MC.  likewise, air dried lumber stored at a dry condition (I store mine in my attic) will be under 7% MC and will not have decay or insects due to the high summer heat in my attic.

So, we should sell lumber based on its MC level and not KD or AD.

Although KD kills insects, once the lumber leaves the kiln, it can be infected with the powder post beetle.

Note that for softwoods, KD means (according to the grading rules) under 19% MC at the time of grading and that the wood was heated to over 160 F.  Note that this sets the pitch real well.

Now, AD lumber can be quite dry.  Check out your local EMC using
http://www.fpl.fs.fed.us/documnts/fpl run/fplrn268.pdf
For example the average monthly EMC in Columbia, SC where I am now is 11.8-14.0.  At home in WI, it is 12.5-15.7. More humid than SC.

[scsmith42]

Gene, you make a good point; I would think that there are three things that a woodworker should be concerned about:

1.  Is the lumber suitably dry for their project needs (6 - 8% for indoor, 16% give or take for outdoor.
2.  Was the lumber dried in a manner that prevented drying related defects,
3.  Is the lumber sterile?

Many of the period furniture restoration folks swear by air dried lumber, as they feel that it works better than kiln dried.  From my own observations, lumber dried in low temp DH kilns seems to work similarly to AD lumber, versus lumber dried at higher temps seems a bit more brittle.

Many of the period furniture guys also say that black walnut that is AD has a more robust color that BW that is kiln dried; and that pigments can leach out of the BW when kiln dried.  Personally, I've not seen a difference in BW either AD or KD in a DH kiln, and the water coming from the unit is clear no matter what species is in it.

One problem with the KD designation is marketing and educating the customer.  Many of the home woodworkers are not familiar with the benefits of sterilization, and many of the AD customers are not aware that low temp drying produces a product that works similarly to AD material.

The biggest pest problem in my area is powder post beetles.  They seem to love oak and if I don't sterilize the lumber the tell-tale exit holes will show up in almost everything.  Do you know if PPB's a problem everywhere, or just in certain areas?

[Jay C. White Cloud]

I can speak to the PPB's topic.  They can be dealt with in a number of ways, including spraying down the wood with just a diluted borates solution in a bug sprayer.  There are also several botanical base sprays but they break down quick in heat and/or UV.  Wood is safe after in reaches a MC below 20% as the different coleoptera (beetles) like powder post, death watch, stages, etc. can't maintain viable eggs with out higher humidity.  In most cases in barns and furniture it is just the larva leaving the would and not a new infestation.   Sometimes in barns when the MC raises because of livestock you may see a re-infestation.  Any type of finish, even a light spraying of furniture polish will deter these different species.

Regards,

Jay

[Tree Feller]

I think you make a very valid point, Doc, but it will take a lot of educating for it to become standard practice. Most hardwood retailers sell their lumber as "kiln dried" and it is actually stamped on construction lumber even though the MC is 19%.

The ones who would probably welcome your suggestion are the hobbiest woodworkers who process their own lumber. Most of them tout "air dried lumber", primarily I think, because they have no easy way to kiln dry their own. Eliminating the designation kiln dried and air dried would eliminate a lot of discussion about which method is better.

[woodmills1]

I read this post with interest :P

[mesquite buckeye]

I can speak to the PPB's topic.  They can be dealt with in a number of ways, including spraying down the wood with just a diluted borates solution in a bug sprayer.  There are also several botanical base sprays but they break down quick in heat and/or UV.  Wood is safe after in reaches a MC below 20% as the different coleoptera (beetles) like powder post, death watch, stages, etc. can't maintain viable eggs with out higher humidity.  In most cases in barns and furniture it is just the larva leaving the would and not a new infestation.   Sometimes in barns when the MC raises because of livestock you may see a re-infestation.  Any type of finish, even a light spraying of furniture polish will deter these different species.

Regards,

Jay

Mesquite powderpost beetles are active even when our relative humidity drops to 5%. No me gusta eses.

[Den Socling]

mesquite buckeye. I may be in Tuscon this week. Do you have a company I might visit? I don't want to bug you personally. I'll have my old dad and wife along but I would like to see your sawing and drying. For just a half hour or so. I'm taking dad down from Phoenix to visit one of his surviving ancient friends.

[Jay C. White Cloud]

Hey M.B.

You just got weird "buggy beetles," there in the desert, but from what I understand, even that subspecies of Powder Post family Bostrichoidea, don't like the dry stuff very much.  They all respond well to the treatments I described.

Regards, 

jay

[mesquite buckeye]

mesquite buckeye. I may be in Tuscon this week. Do you have a company I might visit? I don't want to bug you personally. I'll have my old dad and wife along but I would like to see your sawing and drying. For just a half hour or so. I'm taking dad down from Phoenix to visit one of his surviving ancient friends.

I will be out at the mill in Redington tomorrow and Wednesday if you want to stop by. If you have GPS, that will get you there. Redington is about 5 houses. Let me know if you need more.....

[mesquite buckeye]

Hey M.B.

You just got weird "buggy beetles," there in the desert, but from what I understand, even that subspecies of Powder Post family Bostrichoidea, don't like the dry stuff very much.  They all respond well to the treatments I described.

Regards, 

jay

We don't leave any sapwood unless we spray with timbore first. I've got a buddy who turns bowls who has trouble with his live edges turning to powder even if they are finished......

[Jay C. White Cloud]

Hey MB,

That has happened on museum stuff too.  The little "blighters," are in the wood prior to the wood being used.  There are different treatments.  What is "timbore," I want to add that to my list of remedies.

Thank's

jay

[mesquite buckeye]

Hey MB,

That has happened on museum stuff too.  The little "blighters," are in the wood prior to the wood being used.  There are different treatments.  What is "timbore," I want to add that to my list of remedies.

Thank's

jay

Just a brand name for a borate product.

[Jay C. White Cloud]

I tell you what, those borates products are just plan great, stop the "buggies," natural, easy to apply and a fire suppressant to boot...

[mesquite buckeye]

And less toxic to humans than table salt according to the manufacturer. 8)

[WDH]

This is a very complex topic.  It is also very interesting as nothing is static when it comes to wood.  That is why I love it.

[Jay C. White Cloud]

AMEN...WDH!

[Schramm]

I wish I never would of read this thread as now I am even more lost then before.

Rob

[GeneWengert-WoodDoc]

The lyctid powder post beetle is active from around 30% MC down to about 7% MC, maybe 8% MC.  They prefer the grainy hardwoods for laying their eggs.  Be aware that they are often deep within the wood and can do a lot of damage before they exit.  We see the exit holes.  A treatment applied to the surface will only protect the surface.  Meanwhile, those critters deeper in the wood will go on eating, for a year or more doing a great deal of damage.

In addition to lyctid, we have some PPB brought into the USA that are quite damaging and even like softwoods.  For hardwoods, termites and lyctid PPB are the only insects that attack drier wood.

Borates are very good, but they usually are only surface treatments as the wood is not soaked in the solution so the borates can go through to the middle.  So, borates may prevent a new infestation, but will have difficulty in controlling an existing population that is active beyond the surface.  With some species, we would not want to get dry wood wet again deep into the wood using the borate solution...for example, oak...as that will aggravate checks.

[GeneWengert-WoodDoc]

The early fine furniture makers did not have kilns, but after air drying, they brought the wood into their shop in the rafters near a stove, etc. to achieve a lower MC than they were able to get in air drying.  They would not use the wood straight off the air yard.  They were well aware of shrinkage issues as the wood would dry in the customer's home.  Certainly some farmers used air dried wood for tables, chairs, stools, etc. without further drying.  These items would crack, shrink, etc., but would serve their purpose even though they were not what we would call fine furniture.

Let me be clear that ordinary, open air drying is a risky process, as you can get staining, checking, splitting and warp, depending on the weather.  For that reason, I like sheds for air drying, as the sun and rain, and sometimes wind, are no longer big issues and so quality is improved.  Likewise, in a kiln or predryer, we control drying conditions in order to prevent these defects.

There are a few times when air drying has an advantage...such as oak for barrels.   We will have a vanilla flavor develop and have less tannins with 2 years of air drying with rain.  However, with excellent kiln drying, we can get the same quality wood as with air drying.  It is a myth that air drying gives wood that machines better, etc. than excellent kiln drying.  But in kiln drying, we do have people that do not equalize, that over dry, and do not remove stresses.  They may also rewet the wood when it is partly dry and increase warp.  I have worked with three companies that make musical instruments and they cannot see a difference.  When you see today's high quality reproduction furniture, made with KD wood, it is clear that the quality is equal or better.  Our industry has lots of wive's tales and this stuff about AD being better than proper KD is one of them.  Maybe it is because there are some kiln operators who are more concerned about time and money than quality.

[GeneWengert-WoodDoc]

Regarding borate treated wood, does anyone know if borates can be safely burned?  I am thinking that borate treated wood would be planed and the planer shavings with high borate contents could be made into pellets or maybe burned as shavings.  Is the that safe?  Is the air more corrosive?  What about the high boron content in the ash...can this be put on soil?  Can borate treated wood be composted and used as garden mulch?

As far as Tim-bor being safe, and other borate preservatives, check the link www.prginc.com/Borates/timborlabel.pdf
I am not sure that it is as safe as table salt.

[Ianab]

I am not sure that it is as safe as table salt.

Possibly, but eating enough table salt can kill you too....

Only thing I can find about the ash or compost is that high concentrations of Boron can affect plants. Small amounts are probably no issue (it's probably a vital trace element?) but an excess amount left in compost might be an issue and suppress plant growth, which is sort of the opposite of what you want compost to do...

Ian

[mesquite buckeye]

Regarding borate treated wood, does anyone know if borates can be safely burned?  I am thinking that borate treated wood would be planed and the planer shavings with high borate contents could be made into pellets or maybe burned as shavings.  Is the that safe?  Is the air more corrosive?  What about the high boron content in the ash...can this be put on soil?  Can borate treated wood be composted and used as garden mulch?

As far as Tim-bor being safe, and other borate preservatives, check the link www.prginc.com/Borates/timborlabel.pdf
I am not sure that it is as safe as table salt.

Most soils in high rainfall areas either don't have excess boron or are actually deficient in it, so it would be beneficial in these areas, unless you continually dumped your ash in the same place for a long time. Since borate is so soluble, it will move around with the water.....

Usually to get boron toxicity in nature, you have to be in a desert.

[GeneWengert-WoodDoc]

If you burn borate treated wood, do you still have the water soluble borate salt?  I suspect you have elemental boron...is this soluble in water?  If so, how long before it gets into ground water and then into drinking water.  Cities have deep wells, but many people do not and rely on clean ground water.  Boron is a health issue for young children and pregnant women.  When you spread the ash, the boron is in extremely high concentrations...ash is the mineral part of wood with no wood left in it.

If you sand borate treated wood, what are the issues for the sanding dust?

Spreading wood ash is known to be an environmental issue and I do wonder if spread ash with boron is even more of an issue.  In WI, a special permit is required for spreading ash, but of course not for someone putting ashes on their garden every year.

[scsmith42]

But in kiln drying, we do have people that do not equalize, that over dry, and do not remove stresses.  They may also rewet the wood when it is partly dry and increase warp.  I have worked with three companies that make musical instruments and they cannot see a difference.  When you see today's high quality reproduction furniture, made with KD wood, it is clear that the quality is equal or better.  Our industry has lots of wive's tales and this stuff about AD being better than proper KD is one of them.  Maybe it is because there are some kiln operators who are more concerned about time and money than quality.

Gene, thanks much for the insight on this.  Are you saying that there is no difference in properly dried lumber, irrespective of whether it was dried in a Solar, DH, conventional or vacuum kiln (I'm excluding the ultra-high kilns)?  If so, that is good information to know.

[SwampDonkey]

I will also tell ya that 'most' softwood kilns here in New Brunswick do not get the core up to the 160 F. Only a small number and I believe mostly Irving mills. Irving supplies Home Depot in Canada their lumber.

[GeneWengert-WoodDoc]

Yes, that is what I am saying, but to repeat, not all the kilns you mention would be properly operated by all operators.  I also must say that wood issues can result in defects that are not affected by drying procedures.

[scsmith42]

Yes, that is what I am saying, but to repeat, not all the kilns you mention would be properly operated by all operators.  I also must say that wood issues can result in defects that are not affected by drying procedures.

Understood - thanks.

[mesquite buckeye]

If you burn borate treated wood, do you still have the water soluble borate salt?  I suspect you have elemental boron...is this soluble in water?  If so, how long before it gets into ground water and then into drinking water.  Cities have deep wells, but many people do not and rely on clean ground water.  Boron is a health issue for young children and pregnant women.  When you spread the ash, the boron is in extremely high concentrations...ash is the mineral part of wood with no wood left in it.

If you sand borate treated wood, what are the issues for the sanding dust?

Spreading wood ash is known to be an environmental issue and I do wonder if spread ash with boron is even more of an issue.  In WI, a special permit is required for spreading ash, but of course not for someone putting ashes on their garden every year.

If the wood is burned, you should still have the oxidized form, unless you are making charcoal.

[kderby]

Thanks for bringing this up.  I have a good commercial kiln.  I also appreciate air dry.  I tell people the kiln kills the insects, speeds the drying process and can set the pitch.  Much of what I sell does deserve the insect treatment.  Moist of what I run is a heat treatment process more than a kiln drying process.  I still call it kiln dry.

I regularly encounter the idea that kiln dry means the lumber will stay straight.  People just love to think kiln drying leads to a better product.   I remind them that the Stradavarius (sp?) violin was not made from KD lumber.

The kiln is not a miracle machine.  In my woodworking experience, air dry lumber seems to have a nicer feel than the cooked material.  All of the material goes to EMC anyway.  Still, people ask with a hopeful look, "Is the lumber Kiln Dry?" 

Kderby

[SwampDonkey]

I find that kilned hardwood will chip out easy around pilot holes. If you push a threaded rod through a pilot hole, when it emerges it can splinter. Always have to run a countersink bit at the exit of the holes if your using something that is disassembled and the hole is only a touch oversized and it's not friction fit.

[GeneWengert-WoodDoc]

I would suggest that low MC (under 6% MCe) wood will chip, as you described and not necessarily KD wood.

However, if the kiln uses temperatures in the main part of the schedule over 160 F, we do see some brittleness in the wood that does not go away.  Also, if the kiln uses a very low EMC (50 depression which is about 3% EMC), at least the outside of the wood which is where we are machining, will be over dried and brittle.  A good kiln operation would avoid these extremes, but not all kiln operations do.

[mesquite buckeye]

I would suggest that low MC (under 6% MCe) wood will chip, as you described and not necessarily KD wood.

However, if the kiln uses temperatures in the main part of the schedule over 160 F, we do see some brittleness in the wood that does not go away.  Also, if the kiln uses a very low EMC (50 depression which is about 3% EMC), at least the outside of the wood which is where we are machining, will be over dried and brittle.  A good kiln operation would avoid these extremes, but not all kiln operations do.

I've had air dried hardwoods chip out too.

[SwampDonkey]

Gene, the wood I've used is no where near that dry. I don't have a meter, but it sits for months in an unheated warehouse so it's closer to 16%. And also I would have no idea who the operator was or if they know their stuff. I'm in NB, Canada and the wood comes from as far as Ohio and probably Ontario and lots from right here. Some comes in green and some all kilned. The place has their own kilns for the green stuff. They are suppose to be all certified up here. But if CSA is any indicator of the integrity of the certification, than it's not worth beans.

mesquite, are you talking about holes that are tight fitting or loose? I'm talking loose, but not sloppy loose. I the bottom line is to counter sink to be sure. I notice in particular on bench seats made by loom makers the holes are all sunk.

[mesquite buckeye]

Just from drilling. Same problem on the exit side sawing crosscuts, even with a sharp blade unless I go really slow. My air dried stuff is probably 5% moisture, as our average RH  is probably 20% here. Perhaps it's just so dry the wood is embrittled. Don't know..... ??? : ???

[Ianab]

I've had air dried hardwoods chip out too.

In a desert environment you could get air dried wood down to ~5%. Abusing it in a poorly operated kiln to get it there just makes things worse.

But heck, sometimes wood just chips out because it can.  :D  I've had air dried wood at 12-14% chip out in weird ways.

Ian

Edit: You replied with the 5% air dried comment while I was typing  :D

Perhaps it's just so dry the wood is embrittled

. This is certainly possible. Moisture content certainly affects how wood behaves.

[SwampDonkey]

You get tear out on any piece if you don't use backer board under the piece, the pressure as you thin away the wood near the exit will tear out any wood if not set up right. Even plywood. On the sawing, you need a thin Japanese blade for fine wood working. They cut on the pull upward, not on the force downward. The blades in them are a consumable, toss'm when the teeth go and replace. Kinda like the idea of a hack saw, as far as disposable goes. A regular skillsaw or hand saw is just for roughing.

So, now I know we were talking about something different. ;D

[mesquite buckeye]

You get tear out on any piece if you don't use backer board under the piece, the pressure as you thin away the wood near the exit will tear out any wood if not set up right. Even plywood. On the sawing, you need a thin Japanese blade for fine wood working. They cut on the pull upward, not on the force downward. The blades in them are a consumable, toss'm when the teeth go and replace. Kinda like the idea of a hack saw, as far as disposable goes. A regular skillsaw or hand saw is just for roughing.

So, now I know we were talking about something different. ;D

Even backed up..... still happens if the wood is brittle enough.

A sharp chopsaw is ok if you are slow enough on the cut..... Some of the more brittle stuff chips anyway....

[Jay C. White Cloud]

Hey MB,

I perked up when I heard S.D. mention Japanese saws, a specialty of mine.  I know when I do use dry wood, (unusual for me as I build green 90% of the time :D) like say "Lace Wood," or some "case hardened" tropical, if I use a good japanese saw there is zero chipping.  If you score the cut and use the pull saw. it just can't happen.  Just my two cents...sorry to get off post topic.

Regards,

jay

[SwampDonkey]

Nothing is fool proof. But anyway, my original post was talking about pushing a rod in the hole, not while drilling the hole.

[mesquite buckeye]

Fine, I'm going back to Quicky Quiz Jackpot to pout.

[LeeB]

I think the lack of chipout with a Japanese saw as compared to a western saw is due to the ultra thin blades and lesser set, not the direction of cut. You stilll have teeth exiting from the board. The tooth geometry may also be involved.

[SwampDonkey]

By making the cut on the pull your pulling the fibre toward wood and not toward air. Like a drill press, if you drill against a backer board instead of over a hole, it doesn't tear through. And yes, to the other things as well. There's always something to add if you want to analyze it long enough. ;D Now with the drill press, if you exceed the depth and make a hole into the backer, your next hole is going to tear. Back to square one. ;)

[LeeB]

You get the tear out when the blade exits the wood, it just exits on the side facing you with a Japanese saw. Push cut or pull cut does the same thing in that respect. Has to be blade thickness.

[Jay C. White Cloud]

Hi LeeB and SwampDonkey,

Your both right in a since.  It does have to do with set and tooth geometry.  Lee your also correct about, push or pull, it can still splinter wood either way.

However, what S.D. is getting at is the technique you use with a Japanese saw can mitigate this, or if your trained in there use by someone that actual makes the saw, you should have absolutely none.  I can cut through any species of wood timber, with several different types of Japanese saws, and the tear out is about zero.  If you score the cut, as you should for crucial cuts, it is zero.

Regards,

Jay

[LeeB]

If you score the cut before using a Western style saw you get no tearout. As you said, it's the technique, not just the saw. Just for the record, I do prefer the Japanese style saws.

[bedway]

For what its worth, after woodworking,cabinet making for over 35 years my preference is to work with air dried wood. It is easier on the equipment and is more stable than wood that has been kiln dried. Seems to take finish better in my opinion.

[Jay C. White Cloud]

I hate getting off post... this is good info, shouldn't this be on it's own post?  I'll do it if others think we should so this info isn't lost here under drying wood.

By the way I still like using only air dried or green wood.

Regards,

jay

[mesquite buckeye]

  wait_smiley

[GeneWengert-WoodDoc]

If air dried wood appears to be more stable, it is because you have it closer to its in-use MC, which reflects well on your operation.  Many tests have shown no difference between AD and KD if at the same MC, and if the KD has not been over dried or dried over 160 F and it has been equalized and stresses relieved.

[Jay C. White Cloud]

Sorry Doc,

I was going back to edit what I wrote, but you beat me to it.  I like working in green wood or air dried, as I said.  However, Doc is more than correct, there is absolutely no difference between AD and KD would as long as the drying process of the "kilning," was done well.

Another way to look at it, just about anyone can AD wood.  I find very few KD wood that is of the quality I am accustom to in the wood I work, that could be me, but seems to be the case with many Furniture Makers and Luthiers I know as well.

[SwampDonkey]

I still say on a pull with a saw you have less damage and you have more control. Any time you try to be careful, even with a western saw, you still draw the saw toward you to minimize damage and light touches on the push forward. I always do anyway, that's when being careful and gentle. ;D Both saws require down pressure or you would be sawing air. The damage is always to the underside and sides. And as I said before I agree with all the extras to. It's not just the way you saw. It's a combination. I have cut a lot of wood with both and the Japanese wins on a fine cut, every time. Just take a piece of dowel and use both saws and see the obvious difference. Night and day.

[GeneWengert-WoodDoc]

This is from an article that will be in SAWMILL & WOODLOT called "Sawmill Genealogy."



At some point between the 9th and 5th centuries B.C., the Romans began to use iron and steel for manufacturing saws.  Sometime between 500 B.C. And 50 A.D., these iron saws had teeth that were raked, so that the saw now only cut in one direction; the rake was toward the handle, so the saw cut on the "pull."  Saws were not strong enough (too floppy) to also cut on the "push."  The raked saw, which meant faster cutting, was used for ripping wood and not crosscutting. Cross cutting was done with saws using teeth without rake.

The idea of setting the teeth to make the kerf (the cutting groove) wider than the saw to eliminate binding of the saw developed within the same time period.

[Dodgy Loner]

Sorry Doc,

I was going back to edit what I wrote, but you beat me to it.  I like working in green wood or air dried, as I said.  However, Doc is more than correct, there is absolutely no difference between AD and KD would as long as the drying process of the "kilning," was done well.

Another way to look at it, just about anyone can AD wood.  I find very few KD wood that is of the quality I am accustom to in the wood I work, that could be me, but seems to be the case with many Furniture Makers and Luthiers I know as well.

I agree completely with this point. If you didn't personally kiln dry your wood, then you have no way of knowing if it was done properly or not. Air-drying is hard to mess up, which is why many fine furniture makers prefer it. A couple of bad experiences with poorly kiln-dried wood is all it takes for someone to form their prejudices against it.

[Jay C. White Cloud]

If you didn't personally kiln dry your wood, then you have no way of knowing if it was done properly or not.

Thanks D.Loner, that said it for me best, I'm going to use that, with your permission, because that sums it up perfectly... ;D

[GeneWengert-WoodDoc]

I would add to D Loner's excellent comment

That also is why all major and many smaller wood products manufacturers...furniture, cabinets, flooring, caskets, etc...run their own kilns--so they get the quality that they want and need.