Air Drying vs Kiln Drying

[Jazzflooringco]

Hi I am new to the forum. I thought I would start by opening a new topic with one of my questions of many. I am in the process of milling a 60" bur oak into lumber and then into flooring. We are taking it to a guy in my area to have it dried. He told me that he would be able to put it right into the kiln. I was under the impression that wood should air dry for a certain amount of time before going into the kiln. What are your thoughts on this? Should I be concerned the guy I hired is going to dry my lumber too fast? Thanks in advance!

Also if there are any unwritten rules of the forum that I may not know about feel free to text me @ 262-385-1250. Don't want to step on any toes here...

[Ljohnsaw]

First thing is to update your profile so we know where you are. What thickness are you going to mill the wood? Inch and an eighth? Inch? Seven eighths? Three quarters? The thinner the faster it will dry. I milled some 1" cedar and it lost more than half the moisture in a week. If you are in a dry area, a month of air drying I'll shorten the kiln time.

Drying experts will be a long shortly. There are some oaks that behave well, others that are a pain. I know you don't want to dry ok too fast.

[doc henderson]

Welcome!  the rules are written, but it takes a while to figure it all out.  A few folks never figure it out.  Members here will let you know.  the big stuff, it is a family-oriented forum, not a macho roughneck one, so any foul language will auto correct, or you will be admonished by computer.  If you want to sell or advertise something, you have to read those rules and essentially there should be a donation by % to the forum, state in the text you have read and understand them. 

There are at least two issues.  You must have some knowledge as you asking a good question.  filling in your profile or giving some history about your background will help us temper our answers to your knowledge level.  Oak in general needs to dry slow.  air drying would need to be controlled with medium airflow and no direct sunlight and covered to keep rain off.  air drying can be harder to control, but cheap if you have the area.  Kiln drying is easier to control (the whole point of a kiln) and if your kiln guy is good, he will follow a schedule.  How will you be charged.  Is he busy?  If he goes slow per the schedule and charges by the board foot, all is good.  If he then speeds it up to clear the kiln, then he may damage your load.  if he charges by the day, you may get a big bill at the end. 

A combo of initial air drying then finish in the kiln may make sense.  Much irreversible damage is done early, so if you are airdrying oak, you need to know what you are doing.  A busy kiln might provide air drying initially, and then they need to know what they are doing.  Are you and the kiln operator professionals, or hobby guys?  what is the wood for and for whom?  Your handle implies you are a professional flooring guy?  others will chime in soon.  @YellowHammer @Southside

[scsmith42]

A 60" burr oak would be a great candidate for quartersawing.  You'll lose some yield, but end up with a much more valuable (and stable) floor board.

Presuming that you're milling at 1-1/8" green to make a 3/4" dry flooring board, there is no reason why you can't go into a kiln green with your lumber.  A DH kiln will take around 4 weeks to dry green 4/4 oak down to 8%MC.

A lot of the "internet wisdom" about having to air dry first is a bunch of bunk.  It all comes down to using the proper kiln and kiln schedule.  Yes, very thick woods of certain species are better air dried first, but not a 1" board for flooring.

[Jazzflooringco]

Thanks for the info guys. We are rift and quartersawing it. Super excited. Stopped by the saw mill operator the other day and it's some of the coolest looking wood I have seen.  Drying it down from 1 1/8". Only concern I have right now is I just hope it doesn't crook.

[beenthere]

Could very well crook, as a result of the growth stresses laid down in the tree as outer rings are added each year. 
Just means after drying, that the boards need straightening (jointing) an edge (which is normal before running through a moulder regardless). 

[YellowHammer]

It will most definitely crook, if it is true riff or quartersawn wood, as these techniques will put the stress intentionally in the crook or edge direction (shear plane) vs the face or bow direction. So if done correctly, quartersawn boards will dry very flat with some crooked edges that you can remove later during secondary processing with an edger, SLR, or some multi head moulders. 

Any wood can be kiln dried from green off the mill as long as the proper schedule is followed to never exceed the max allowable moisture removal rate as well as the temperature profile to not cause enzyme stain, or other issues.  However, drying from green is fraught with danger as many serious drying defects occur in the initial stages of drying. So the question is what are the credentials of the kiln operator?  What drying schedule is he following?  What kind of kiln does he have and how long has he been doing it?  There is a very narrow error band between high quality kiln dried wood and cracked garbage kiln ruined wood. 

[jimF]

As mentioned, the green state of the wood in a drying condition, sun exposure, breeze, is when most damage is done, ie. on the green chain. For oak, surface checks are easy to start, can never heal or cure it once it starts. As also mentioned, air drying has almost no control and kiln drying is a method that is able to have the most control.

On the green chain stack under a roof and block any breeze. During air drying cover with a roof to protect from rain and sun. Use of "shade-dry" can be used to reduce air flow through the stack. If the wood smells like vinegar it is bacterially infected and is more prone to surface checks.

It is possible to cause staining in oak but not the biggest concern; just keep an eye on it and if mold develops increase air flow..

[Ianab]

The reason for air drying first is to reduce the time that the kiln is tied up. You can of course dry from green in a kiln, but you have to set the schedule to one that's safe for thew wood type. As mentioned above, white oak might take a month in the kiln, and you have to operate and charge for the kiln time by the day. Now if you can get some air drying in first, that cuts down the kiln time. So maybe air dry for 6 months, then it only needs a week of kiln time to finish. Now you are able to get a lot more wood though your kiln each month. 

Down sides are that air drying isn't well controlled, it's possible to mess up some species by drying too fast (or too slow). Other one is that you now have to wait 6 months to be able to use or sell the wood, and that has an economic cost involved. 

So the best method depends on "things".  

You can ruin wood by poor air drying or poor kiln drying. Try and up the drying settings to get that oak dry in 3 weeks, probably ruin it. Set it out to air dry in the middle of Summer in a dry climate, same. problem. 

[customsawyer]

I would be a little cautious of a kiln operator willing to take green oak strait to their kiln. It can be done but ties up the kiln longer.

[scsmith42]

Thanks for the info guys. We are rift and quartersawing it. Super excited. Stopped by the saw mill operator the other day and it's some of the coolest looking wood I have seen.  Drying it down from 1 1/8". Only concern I have right now is I just hope it doesn't crook.

You can reduce the amount of crook by minimizing the amount of juvenile (pith) wood along one side of the board, and minimizing the amount of sapwood along the other side.

For the best figure, use Yellowhammer's "Reverse Roll" quartersawing method.  It will yield 75% or greater high fleck boards.  You can read up on it on this forum and on Yellowhammer's Facebook page.

For the best compromise between milling speed and amount of high figure, use the "Woodmizer" method of pulling 3 or so boards from the middle of the log, and then putting the remaining 1/3 log sections face to face stood up ont he mill and mill down.  This will yield around 50% high fleck, and 50% low fleck / rift.

Removing slab offcuts to turn the log into an octagon before milling will help reduce the crook related to sapwood.

[jimF]

This the first time I've seen anything concerning reverse roll.  I put that in the search engine and just get articles referring to it. Does anyone have a link to the description?

[doc henderson]

It was done at a sawing project, and I think 123maxbars has a you tube of the event.  It is the second half of the video.

https://www.youtube.com/watch?v=zNwzXUzHhMk&t=106s


here is one thread.

Reverse Roll Quarter Sawing - Page 4 (forestryforum.com)

[longtime lurker]

I'm going to be a bit of a heretic here and say kiln drying is way overrated unless you own a sawmill.

Anything made of wood pre mid 1800's - and that's less than 200 years ago - never saw the inside of a kiln. Now the argument goes that pre air conditioning and central heating wood never needed to get below EMC kind of overlooks the inconvenient fact that people actually keep  Louis XIV furniture or great grandma's rocker inside their 200 year old house- that's been updated to include all the mod cons - with little thought that apparently it should all collapse around their ears. Wood moves with moisture shifts and the two greatest factors to long service life are wood quality and quality of workmanship, not moisture content at manufacture.

Kilns used to be the preserve of big mills due to cost of installation and the big mills pushed KD as an ours are better than yours thing for a century. Lower capital cost equipment  changed that after WW2, and the building and manufacturing industries were quick to take advantage of the initial working stability of KD lumber to go to faster and easier so cheaper jointing and fastening methods. If KD was so much superior you should expect a chair from Ikea to outlast great grandma's aforementioned rocker and we all know how that will turn out. I know of one great grandma's rocker built by great grandpa in West Texas that's been around the world in every thing from desert to tropical jungle and back to Texas and is still in service. Great grandpa didn't have a kiln, he just knew how to build things to last.

Nope, KD lumber is a rort, and the only real beneficiaries of it are sawmillers because what a.kiln really does is not improve lumber quality so much as it improves the sawmillers cash flow cycle, and that's why I need more kilns, cuz I can't wait for lumber to air dry to get paid.

[Magicman]

This is framing lumber and not actually related to the topic subject, but it may interest someone about sticker drying framing lumber:

In the 1950's, I remember seeing lumber stacked at sawmills in a sorta stepladder arrangement, crisscrossed at the tops.  The lumber for the home that I grew up in was stacked that way and I remember watching my Granddad flipping it end over end.

I stopped counting several years ago when my number of "whole house" framing lumber jobs reached 25, and I am quite sure that it is easily double that now.  The lumber is stickered, never kiln dried, and used whenever the building need arises.  I seldom get to see it after sawing but I do have a few pictures:






Store bought framing lumber has been dried to 18% and stickered SYP lumber will easily dry to below 20% within a couple of months.

[scsmith42]

I'm going to be a bit of a heretic here and say kiln drying is way overrated unless you own a sawmill.

Anything made of wood pre mid 1800's - and that's less than 200 years ago - never saw the inside of a kiln. Now the argument goes that pre air conditioning and central heating wood never needed to get below EMC kind of overlooks the inconvenient fact that people actually keep  Louis XIV furniture or great grandma's rocker inside their 200 year old house- that's been updated to include all the mod cons - with little thought that apparently it should all collapse around their ears. Wood moves with moisture shifts and the two greatest factors to long service life are wood quality and quality of workmanship, not moisture content at manufacture.

Kilns used to be the preserve of big mills due to cost of installation and the big mills pushed KD as an ours are better than yours thing for a century. Lower capital cost equipment  changed that after WW2, and the building and manufacturing industries were quick to take advantage of the initial working stability of KD lumber to go to faster and easier so cheaper jointing and fastening methods. If KD was so much superior you should expect a chair from Ikea to outlast great grandma's aforementioned rocker and we all know how that will turn out. I know of one great grandma's rocker built by great grandpa in West Texas that's been around the world in every thing from desert to tropical jungle and back to Texas and is still in service. Great grandpa didn't have a kiln, he just knew how to build things to last.

Nope, KD lumber is a rort, and the only real beneficiaries of it are sawmillers because what a.kiln really does is not improve lumber quality so much as it improves the sawmillers cash flow cycle, and that's why I need more kilns, cuz I can't wait for lumber to air dry to get paid.

LL, I think that the benefits of kiln drying will vary depending upon where in the world / country that your lumber is sourced.

My my area (NC USA), we have a lot of lyctid powder post beetles that will inhabit milled lumber.  The sterilization cycle performed at the end of the drying process will kill the beetles, their eggs and larvae, preventing an infestation from occurring after the flooring is installed.  If for no other reason, kiln drying is highly advised for lumber produced in my area that is destined for indoor use.

[Stephen1]

KD is beneficial north of you here in the land of freezing and boiling. Our houses moisture swing so much. LL our 200 YO old furniture is not that great. 

[Magicman]

our 200 YO old furniture is not that great

But it has character and it's home. 

[Larry]

During the winter, I heat my shop 24/7 with a wood stove. The shop is toasty warm with very low humidity due to the wood heat. If I bring air dried wood into the shop in the early fall within a few months the MC will drop to the same MC as wood fresh out of my kiln. The wood will remain at this level until late spring (actually I air condition so once dry wood stays fairly dry).

I suspect the woodworkers 200 years ago did most cabinet work in the winter using low MC wood from wood heat in the shop. During the warm season they probably were out logging, running the sawmill, or farming. Not much got made during this time.

I have no idea, but I'm guessing most of the furniture built 200 years ago is gone due to poor construction, misuse, or even barroom brawls. Only the high end stuff has survived and we don't know how many times some of that has been rebuilt.

[doc henderson]

or it was an expensive piece, and no one was allowed to set on it for 5 generations.  

[longtime lurker]

LL, I think that the benefits of kiln drying will vary depending upon where in the world / country that your lumber is sourced.

My my area (NC USA), we have a lot of lyctid powder post beetles that will inhabit milled lumber.  The sterilization cycle performed at the end of the drying process will kill the beetles, their eggs and larvae, preventing an infestation from occurring after the flooring is installed.  If for no other reason, kiln drying is highly advised for lumber produced in my area that is destined for indoor use.

I don't disagree with that Scott but the same argument applies... there are plenty of items about that pre date the common use of KD lumber and the borers haven't eaten them yet.
And you know as well as I that heat sterilization will kill borers but should the material get wet again borer re-infestation can occur. I also know that you guys now have far more restrictions around the use of chemical barriers to insect pests than we do here.  Was it always that way in NC or was the use of borates, oil or pitch or some other preventative common there 100 years ago? Lead based paint would be pretty effective too I'd imagine.

I'm not saying kiln drying isn't a good thing or that its sometimes not the best thing, so much as that there are more than one ways to skin this particular cat.  As a processor the main benefit of a kiln I see is the accelerated cash flow cycle through not having to wait a year an inch for wood to dry, every other benifit of kiln drying has an alternate historically proven solution.

[Peter Drouin]

Bring a  M meter to a big box store and check the lumber, you might be surprised. I do air dry some before it goes in the Kiln.

[doc henderson]

I am not sure the lead in paint kills borers, but they tend to have a heck of a time with math.  

[Ianab]

When you look at (surviving) old furniture you will see it's been built with wood movement in mind. The stuff that wasn't has fallen apart years ago. 

Here in NZ it's often humid, but houses aren't climate controlled. We have basic heating and usually AC now, but it's only intermittent use. Generally you open a window if you want cooler, unless it's the middle of Summer and hot outside, then we now have a heat pump / AC. But average humidity year round is in the 60-100% range. Met Service says humidity is 88%, and temp is 17C. Couple of degrees warmer in the house, but not by much. So building with wood dried to US standards could actually be a problem, it's going to suck moisture from the air, and expand. Some companies import KD flooring (oak etc) from the US, but before it can be used reliably they have to unpack and sticker it, to GAIN moisture before the floor is laid. Putting down 6% wood in a 12% house is even worse that the reverse. 

The comment about killing bugs is valid, if you have air dried wood it's possible for borer to get into many species, and then hatch out later in someones dining table. NOT a good look. But kiln drying doesn't prevent re-infestation later on. What generally protects furniture is a film finish. Be that varnish / shellac / paint / wax etc. The female beetle is wandering around looking for a place to lay eggs, and the trigger is tasting cellulose, that means it's wood, and a good place to lay eggs. If all she tastes is polyurethane (or anything that's not wood), no point laying an egg there. But when selling wood that's susceptible to borer, having the peace of mind that "there are no live bugs in there" is a good thing. So again, that old furniture either had some finish (shellac / wax / curing oils) or was a species of wood that naturally resists borer attacks. 

[jimF]

Shops here in the US 200 years ago were not sealed as tight as what we have now. In the winter, at least in the south, is very damp, 15-18 % EMC, if there is no modern insulation and house wrap on the house