Drying re-visited

[Ken - Ottawa Valley]

I wanted to share some information regarding the earlier post on kiln versus air drying. I researched the topic in the US Forest Products Laboratory’s Wood Manual because of its importance to what we do. It’s pretty obvious that the wood we use should be at the moisture content equilibrium expected in its final use. For interior applications this is averaged at and recommended to be 8% throughout the continental US. Air drying wood, given sufficient time, can bring the moisture content down to only 12-15% in most regions. (Interestingly this varies from 4% (Reno in June) to over 18% in Juneau). For furniture building you are more likely to have problems in the future if you use air-dried stock versus wood that has been kiln-dried to somewhere in the range of 7-9%. Moist, coastal areas can use 11% as a guideline for furniture stock but they also have a much higher equilibrium moisture level achieved through air-drying alone. I realize this may be controversial but the FPL is a respected source and their research merits consideration in the debate. -Ken

[Ken in Regina]

Thanks for the follow-up, Ken. Now, does anyone have some sources for an inexpensive moisture meter that's ballpark accurate??

[Bill Guthrie, Toronto]

I use the mt110 from Electrophysics about $110 and accurate. It goes up to 40% so useful when you are drying wood from green.

In my experience 10% is sufficent here in Ontario. This can be acheived by bringing your airdryed 15% inside in fall and winter, provide airfloe and a dry atmosphere and 75 to 80 degree temps and in a month you will have 10% or less.

Many projects with my home dryed oak and no problems. See link below. Bill G

http://www.electrophysics.on.ca/pins.htm

[Roman]

A simple method for measuring moisture content.

cut a piece off and weigh it and record the weight. preheat your oven to 214 to 221 degrees. Bake the wood until the moisture is gone. A couple hours. Weigh the wood again.

weight when cut- oven dried wood
-------------------------------- X 100= moisture

oven dried weight content

the longer you bake it the more accurate the read.

[james]

As Ken stated, the fact that you can take air-dried lumber into your heated home and shop and equalize is definitely possible. There are two things to consider. Do you have the time and do you have the space?
You will have to cram all your drying into about a five month period when your storage area is heated. If you do not get a batch done before the heat goes off you will have to wait until next year.You will be limited to the amount you dry in a confined space and a dehumidifier may be required if the relative humidity becomes to high.
If the moisture in the air rises, the point at which the moisture content stabilizes will also rise. The dehumidifier will be needed to bring it back down.Thus increased energy costs.

"The reason you kiln dry is to eliminate that time. With proper kiln drying you can use the lumber immediately."

Moisture content is the big issue here.If you use fully air dried material outdoors you will have very few problems. If you are steam bending material you do not want kiln dried material because it is much less pliable and will more likely to break.
Kiln drying prepares your wood for indoor use and stablizes it to an indoor enviroment during that enviroments driest period.
A friend built a beautiful set of oak raised panel doors for his new kitchen. He was a beginner and used air dried material.He put a beautiful dark stain and then put clear finish coats over top. He installed the kitchen in the late summer. Come January he noticed about a 1/16" line on the outsides of his panels where there was no finish. His panels had shrunk and areas that were under his stiles that had not been finished were now exposed.Needless to say he had to remove the doors so he could strip sand and refinish the doors. Had the wood been dry he would not have had this problem.
Do yourself a favor and buy a moisture meter or ask your retailer to take a reading for you. If they are unable or unwilling then approach your purchase very cautiously.

Hope this helps.
James

[Ron Evers, Beeton, ON]

Hi Roman.

The method you describe is how the MC of materials is determined in a laboratory where accuracy is paramount. No moisture meters used there. It is known as drying to a "constant dry weight". The specimen is placed in the oven, taken out and weighed at specified intervals and when the weight does not change from one reading to the next it is dry. Leaving it in longer can change the physical characteristics of some materials and produce erroneous results. For instance, if we were trying to determine the MC of a sample of asphalt pavement, leaving the sample in the oven beyond the "dry" point could start driving off some of the lighter oils and give false results. All this said, you need a very accurate weigh scale, which few of use would have at home.

Best Regards, Ron.

[Ken in Regina]

Those are excellent points, Ron. I have a fairly accurate scale that I use for weighing golf club components. It's a high end food scale and weighs to a tenth of a gram. Wood that be good enough?

If I chose to use the laboratory method, how frequently would you suggest I check? If I was starting with wood that I suspected was already dry enough or pretty close?

I'm not sure I have the patience for this method, but I'm equally sure I don't want to pay $100 for a meter, either. Maybe I can find one cheaper.

[Ron Evers, Beeton, ON]

Ken, According to ASTM D 4442, for a precision level, of 0.5% MC, a Minimum Balance Sensitivity of 5 mg is required.

Oven: Convection oven that can maintain 103 ±2°C.

Sample size: 50 by 100 mm in cross section and 25 mm along the grain. This size specimen will usually attain constant mass in 24 h.

The endpoint has been reached when no appreciable change is noted in readings made at approximately 4-h intervals.

Fun stuff eh?

Best Regards, Ron.

[Ken in Regina]

Actually I find it very interesting, Ron. It's just not very likely that I'll do it. First, I don't have a convection oven. How frequently do you suppose I would have to open the oven door, and for how long each time, to simulate it? [grin]

Second, the oven in our electric stove isn't likely tolerant to +/- 103 degrees, never mind +/- 2% !! And constantly opening the door to allow the moisture out won't help any. [chuckle]

...ken...

[raymond from the sault]

james: are you saying that if i but kiln dried lumber that was dried to 6 0/0 it will not react to the moisture in the area that it is stored ie 10 0/0 in my shop, it will stay at 6 0/0. ray

[Don in Brantford]

Tell your friend to finish the panel first before assembling the door door so that sort of problem is avoided.
Don

[james]

Ray
If material is kiln dried to 6% and is introduced to an enviroment of higher humidity it will eventually pick up moisture. It will stablize to that enviroment. It does not happen over night but may take weeks or months.THe best example I can think of is a wood door or window.In the winter it fits fine and in the summer it is sticky or tight.In summer the humidity rises,the door picks up moisture and expands and thus becomes sticky.

[Roman]

Hi Ron

Yes Ron this how they do it in a lab but it is also a cheap and relativily easy way to do it at home. I feel the shavings after running it through the planer myself,if I use air dried lumber.

I have access to a triple beam and there are cheap scales at any head shop that are reasonbly accurate. Not all smokes are tobacco so to speak. Its a great idea to keep taking it out to see when the weight quits changing.

I think the point being was " is air dried lumber as good as kiln dried". I guess that the real question should be is what is the relative humidity where it is being built? versus what is the relative humidity is where it will sit when finished?, assuming the wood is stable. You can build a piece of fine furniture in Edmonton in the winter and ship it to Vancouver where the humidity is far different which in turn affects the furniture.

Is air dried better than kiln dried..... ? care to answer that one. The answers are far more complex and so many factors must be included. Humidity and moisture content are just the beginning.

Cheers

[Ron Evers, Beeton, ON]

Roman, you ask, "Is air dried better than kiln dried..... ? ". I am not sure, but for a given MC, I would personally prefer air-dried. Why, because the drying process has taken place over a longer period of time and stresses in the wood have had a chance to relax, i.e. less chance of "case hardening". As a hobbyist I am able to work this way, however it is not practical for folk such as you in commercial enterprise.

Certainly changes in the environment must be a consideration when working with solid wood furniture. I made a dresser and front fold-down desk for our son out of ash, which was stable in our home for several years, and when he moved to his own home with electric heat (no humidification), panels in the furniture split within the wood. Similarly, some of our own living room walnut furniture and oak dinning room floor cracked, after many years without problems, after we installed a wood burning fireplace insert. The problem was no humidification from our oil furnace/humidifier because the fireplace became our primary heat source. We have finally, this year, purchased an independent stand-alone humidifier.

Roman, from the tone of your post, I have the impression you thought I was being confrontational, I assure you this is not the case.

Best Regards, Ron.

[Roman]

Howdy Ron

I can assure you Ron of one thing and one thing only.

You are a great guy and I frequently if not always look up your posts and always know that what you speak is the truth. I frequently use your knowledge of materials, wood included to my advantage. I have placed bets on your postings and Ive never lost yet. When I want an answer about wood and its properties... what can I say .... you always have the answer

It is my nature to be the devils advocate and it is often that this is percieved as confrontational. for all of you that percieve it this way Im sorry

I personally believe that kiln dried lumber is far superior in any application of building wether it be framing a home or building a fine piece of furniture.

In any of the personal pieces of furniture that I have in my home and not to be confused with commercial work, are made with KD. If I had a choice I would make mine with the KD.To argue about it, thats silly.

The longer wood sits and settles its own arguements the less chance you might have to argue with it later. So long ago jointers passed there trade along, with wood that might have been aged for generations. If those guys had a kiln would they speed up the process?

Kiln drying through scientific methods that use absolute measurements with accurate scales and convection ovens cant do what I could if I had the time, but then again I dont have the time. lol

I think it comes down to money Ron. Anyone who tells me they have a butt roast that is better than a prime rib roast has convinced themselves and there is nothing I can do to convince them otherwise. Not to say I wouldnt stay for dinner.
and certainly not to say thatI wouldn't enoy the dinner. I love pork too.lol

Regards Roman

[Steve in Kemptville, On.]

Since I bought my M. Meter I have found that the air dried lumber I have stored in my garage is <10% even in the summer. I brought it up to my shop for about 1-3 weeks and re-measured and it was down to 7-8%.

KD lumber will take on moisture just like air dried. Most people go to a lumber yard, pick out thier stock and away they go. Problem is that the stock has been there for a while, not fresh out of the kiln which means it will no longer be 6% (in the summer) but has more likely stabalized to a higher MC. Point is, if I take a piec of my air dried wood and a similar KD board and stick them up in my shop for a couple weeks as you would when building a project, I'd bet that the MC will be the same between the 2 samples in no time.

If it's air dried to 10% it will only take a couple weeks to get it to stabalize with your shop environment (stickered for air circulation naturally). The same would be true for KD (in reverse) so in your shop it would likely stabalize to the same MC in about the same time but coming from the other direction.

Bottom line is that if you can get Air dried lumber at 10% or less I see no real advantage to KD in the end. The big advantage is for the suppliers as they don't have to wait 2 years from milling to have a saleable product, a lift of Oak could go from green to 6% in a matter of weeks.

About the panel movement... As others have stated staining the panel first is a must and will solve the problem due to seasonal movement.

My 2c.

[KOOTUR Lumber and Sawmill]

More often then not the hottest debate is over Moisture Content in wood. Back before kilns the industry was at the mercy of Mother Nature. Then came quarter-sawn wood, a bandage but never the less one type of solution for stabilizing wood movement. The industry demanded more, the invention of kiln to speed up things. And so, the birth of kiln dried lumber, however all kilns are not the same. There are many system and many different ways to kiln. To add to the confusion we add the fact that not all kiln dried lumber is dried to 6-8% example construction grade 18%. Storage and shipping is always interesting topics as well.
The water itself within the cell is a complex topic; you must understand the cell structure of the living tree. The different species of wood is an issue as well. We didn’t even mention how to use moisture meter and how they apply to wood. Courses are offer on each and every one of these topics. The key is you must take in account all the different area of concern. We will be offering a course that will include from tree structure to method of cutting and drying in the near future though one of the colleges. We will once again address this topic in an upcoming issue of Canadian Wood Working if we have enough space.

Once again information that everyone is adding is great. This issue is not a simple one it is complex deal over many different fields from tree structure to kilning to meters.
And last but not lest if we use the butt or prime rib theory (Roman-posting) its better to consider that the meal would be of the same type of roast, the difference is in the cooking!!!! I guess it all comes down to the chef………..Woodworker abilities to make the best with what knowledge you've learned.