drying wood

[Barry wines]

I,d like to discuss wether to air dry or kiln dry wood.Me and my two boys have accumulated about 4000 to 5000 board foot of various hardwoods. Some from farmers who have let us have some downed trees, some from the shed of my late brother in law and I have purchased some logs from a timber man. Some of the wood has been in a shed for 50 years but it does,nt matter it still moisture tests 12-14%. We havn't had any disasters but we have had more shrinkage than we would like and one book shelf that has a slight warp.
Air drying;
Advantages:
1. Grain is more prominate
2. Wood machines better
3. Bends better

Disavantages:
1. More movement from seasonal humidity changes
2. More potential for warpage

Kiln drying:
Advantages
1. More stable. According the guys at the kiln all of the water in
the inner cells is evaporated and the cells are collapsed precluding
their ability hold moisture and the heat hardens the wood tissue
making it more stable. They said although all wood will experience
some movement it will be much less than air dried wood.

Disavantages:
1. cost if it is not necessary
2. Loss of the ability of the grain to stand out

I have 2 loads being dried right now But I have read in fww statements
by some professionals that they don't kiln dry their wood that they use for fine furniture. what do you all think? Thanks Barry

[Danny Hamsley]

If you kiln dry it and store it outside in a shed, you are wasting your time because the wood will eventually, over a series of months, gain moisture from the humidity in the air and equilibrate back to the 12 - 14% moisture content range. You have to store kiln dried wood in a humidity controlled environment if you want the moisture content to stay the same. That is not easy to do for 5000 BF unless you have a large heated and cooled shop or other such space.

[Barry wines]

The wood that I have taken is only a small portion of the wood that I have stored in the enclosed leanto. I took some of several vareties that I thought I might use in the coming months. What I took to the kiln will go in the work shop which is heated when I am working,which is often.

[Rich Aldrich]

I prefer kiln dried wood because of the stability. I was unaware of wood being more difficult to machine after kiln drying. As long as the wood is kept dry, only the outer layer will absorb moisture. If you leave it rough cut, you will machine of the outer layer that absorbs the moisture. Be sure to seal the end grain with sealer in either case.

Once it is kiln dried, store the lumber stacked without stickers. Only the outer boards are exposed to humid conditions. However, make sure the lumber is off the floor with stickers and make sure it does not get wet. This is a recommendation from the person who sells me rough cut at a reputable sawmill.

[Quinn McCarthy]

Barry,

I wouldn't use anything that wasn't kiln dried. People think that the longer you air dry a piece of wood the drier it is. That is not the case. Once the wood reaches equilibrium that is were it stays. If equillibrium takes a month or a year once it is there that is it. There are a ton of people that I run into that only use air dried. There is a lot of bending and twisting open miter joints. Where I am located it goes from 70% humidity in the summer to drier than the sahara desert in the winter. The kiln dried wood doesn't change with the seasons. Most of the work I do is for other people. It is worth the cost of kiln drying to have a peace of mind when the piece leaves the shop.

I hope that doesn't sound like a rant. Hope that helps.

Quinn

[Frank Drew]

Barry,

I wouldn't use anything that wasn't kiln dried.

You're missing out on a lot of nice wood, then. Air-drying certainly requires a lot more patience than kiln-drying, but the results are good, but I'm not going to get into an argument that one is better than the other all ways/all times.


The kiln dried wood doesn't change with the seasons.

Ha ha.

[James White]

Barry,

You don't have your location filled out in your profile. That can make a difference.

If you have the time. You can move your lumber in to a conditioned area. That area needs to have the same relative humidity as the final location of the piece of furniture. It is best if you have a moisture meter for this. It will take a min. of a month two months would be better. Even two months may not be enough if the equilibrium moisture content (EMC) difference is big.

Kiln dried wood does move less in general but it still needs to be acclimated to its final destination. Again a moisture meter is best.

A shop conditioned only half the time is not going to cut it. Also the idea that only the outer layer will be affected is only true for a short period of time. You need to think of the wood as a slow sponge. If it is exposed to humidity it will absorb it.

Edit: The best way I have found is to have a dehumidifier in my shop along with an inexpensive hygrometer. Then you can keep the humidity exactly were it needs to be. You can find digital hygrometers for less than $20. I keep one in my house as well. This lets me know better what humidity to keep my shop at.

James

[Jon Grider]

I use both. The fact that many museums and historical sites have 200 year old pieces of fine furniture constructed with joinery that takes into consideration wood movement and built with air dried wood illustrates that air dried wood can be used for interior applications. Another plus, of course is that bargains can be had for air dried wood.
One downside that has not been addressed in this thread is the ability to kill wood boring insects that the kiln affords. I try to inspect air dried wood very carefully before purchasing and bringing it into my shop.

[Scott T Smith]

Barry, I operate a kiln. Here is some additional information.

Re disadvantages to AD wood:

3. It is not "sterilized", and any pests such as powder post beetles, termintes, larvae, etc that were present in the log or milled boards will be present in your finished wood.

4. If the wood is a resinous wood such as pine, AD lumber may continue to bleed the sap out over time, and also gum up your tooling.

There are several different types of kilns; the most common three are Conventional (High temperature), Dehumidification, and vacume. Conventional is the most prevalent, and the "negatives" regarding KD wood are usually in reference to KD wood that has been dried at a high temp (machining problems, etc).

DH is the second most prevalent (although a very distant second place), to my knowledge there are no problems with grain standing out, machinability, etc assoicated with the low temperature DH process.

Vacume kiln dried products are probably the best, but vacume kilns are low volume and not very common.

Different species and board thicknesses react differently to the drying process too. For some species that lend themselves to air drying and are naturally bug resistant (cypress, cedar, walnut), air drying is a great option.

The prevailing temperature when the logs are harvested, how quickly that they are milled, and how quickly they go into the kiln also makes a difference in the ultimate appearance of the wood. Fungal degrade is not as common in woods harvested during cold months, and the daily drying rate is also reduced, so air dried wood that is harvested and milled during the winter, and then finished off in a kiln can provide the best of all worlds.

[Barry wines]

Thanks for the input guys. I live in northern Ohio and the humidity can get fairly high so by next summer I will get a dehumidifier for the shop. My friend the timber buyer talked me into taking a Hackbery log. I was hesitant because of what I have read about it going bad but he told me that when cut in the winter and gotten into a kiln that is not a problem. Besides he said that it has good machinability and dramatic grain that really pops out after it is stained.

[Karl Card]

i am a newbie getting ready to make my own kitchen cabinets. when i questioned the drying methods i was told by a professional to kiln dry then after you get wood home let it set in your kitchen (or in the house where feasable) to let it adjust to the humidity of the house.. then the warpage if any will be very moderate.

[Ed Bath]

Barry,

The moisture content of wood depends on the relative humidity and temperature of the surrounding air. For outdoor storage in northern Ohio, completely air-dried wood averages from 12.6 percent in the spring to 14.6 percent in winter. This is the equilibrium moisture content (EMC). So your moisture readings seem about right.

As temperature and humidity change, the wood will gain or lose moisture. This will definitely happen when you bring the wood indoors to an air conditioned/heated building. Typical EMC inside homes is in the range of 6% to 8%. That is the level that kiln operators shoot for.

As the moisture content of the surrounding air decreases, the wood will shrink in width (but not much in length). The amount of shrinkage depends on the type of wood and whether it was flat sawn or quarter sawn. Quarter sawn shrinks a little less.

For example, a flat sawn, ten-inch wide white oak board going from 13% moisture content outside to 7% inside will shrink a little more than ¼ inch in width. Your hackberry will shrink about 3/16 of an inch. As the wood shrinks, it can also warp and cup. Surfaces that were sanded perfectly smooth will become wavy (believe me, I’ve done this several times!).

I would be very concerned about the advice that you got from the guys at the kiln. The last thing that a kiln operator wants to do is collapse the cell walls. That would distort the board so severely that it would be useless. The purpose of kiln drying is to remove most of the water quickly without destroying the wood.

If you need to store already dried wood without it gaining any moisture, the easiest way is to keep it at about 20 degrees warmer than the outside temperature, like in an attic. Otherwise, storing it in an air conditioned/heated building would work (under the sofa?).

I apologize for the long reply, but the relationship of wood and water is very interesting to me. I wish I would have known more about it before I bought a sawmill. It would have saved me a lot of time and aggravation!

Ed

[Eric Sayre]

Barry, while kiln dried is generally trusted more than air dried, don't be afraid to air dry your lumber (or some of it.) I have 2 large lumber racks loaded with about 2,500 bf of various lumber. 60% of which was cut down and air dried.

These racks are located in my shop, which remains unheated/uncooled about 6 days/week. There is a lot of humidity here. There is little or no difference in moisture content variation between my KD & AD lumber.

There will be challenges in the drying process, however. Make sure you stack it flat and weight it down. You can't get too much weight on top of the stack. Do a little bit of research on the hardwoods you will be drying; I found out (the hard way) that pecan has a strong desire to warp if not stacked and weighted soon after sawn - Hackberry has a tendancy to become covered with blue spots (mold).

I've built many projects with my air dried lumber and it all looks great. The only two things I don't like about air drying are 1) Takes too long, and 2) Takes up a lot of space.

Good luck, whichever you decide to do!