moisture content

[Lynn Reid]

Hi...I just bought a load of spalted maple from a sawmill. It has been air drying outside and uncovered for 2 years. The moisture content is anywhere from 10-13% What I plan to do is make 2" rails and stiles for cabinet face frames and cabinet doors. Is that doable at that moisture content? I live in South Carolina and it has rained practically all summer...in addition to the high humidity. I would think the movement would be minimal for a 2" rail/stile at 13%...but I wanted to ask the experts before I make the face frames. A few of the boards are 15" wide and 14' long...although they aren't nearly as spalted as I would like. I wonder also if they would be stable enough to make raised panels for cabinet doors. Thanks!
Lynn

[Richard Coers]

Also consider any insects that may be in the wood. Spalted and sitting outside for 2 years is asking for bringing bugs, and wood eating bugs, into the house. I'd have it kiln dried just for that reason. Wetter wood may not shrink much, but if you do any longer doors, like pantry doors, it may move a little.

[Lee Schierer]

In my opinion 10% is too high to work with. Typically kiln dried will be 7-8% after adjusting to your shop. Making parts with lumber at 13% will likely result in noticeable shrinkage and potentially warp, twist and or cupping of finished parts. Get your lumber in side for at least 6 months to a year before investing time and energy working it or get it kiln dried.

[Bill Davis]

My question would be... What is the average relative humidity where the project will reside? If it is 55 to 70% then 10-13% MC will be just about right. If it is more like a normal home of 25 to 40% RH than the woods MC should be closer to 5-7%. The more difference in the MC could result in dimensional and warpage changes in the finished produce. And depending on whether the wood is more plain sawn vs quarter sawn Maple has an approx. 4-10% shrinkage in radial vs tangential direction. Rail & stile construction is frequently used to minimize effects of dimensional changes due to RH changes so you might be OK but... If it were me I'd like the wood MC be closer to 5-7%. Particularly if there are drawers and doors or any close fitting construction involved.

[Danny Hamsley]

Your equilibrium mositure content in your house in SC will be more like 9.0 - 9.5%. In the North, it will be lower. I know because I have measured it here in GA. It depends on your area and climate. 5 - 7% here would result in wood swelling, and that would cause problems with our humidity. If you allow for shrinkage in your design and do not have cross-grain joints, you will be fine. The shrinkage on the rails and styles will not be noticeable, and you could make the grooves for the panels a little deeper. You do need to finish the panels before glue up so that any shrinkage will not reveal unfinished wood. You could bring the maple inside for about 3 weeks and stack it with spacers and it will dry down to equilibrium. Maple is one of the faster drying woods.

[Mark W Pugh]

In my opinion 10% is too high to work with. Typically kiln dried will be 7-8% after adjusting to your shop. Making parts with lumber at 13% will likely result in noticeable shrinkage and potentially warp, twist and or cupping of finished parts. Get your lumber in side for at least 6 months to a year before investing time and energy working it or get it kiln dried.

Question. I have a lot of cherry that has been stickered in my shop for about 10 years. Moisture content still at 10%. I live in SE OH and the boards are only 1" thick. Even if I kiln dry it, won't the moisture content rise once stored back in the shop?

[bill tindall]

Glue issue. At that high moisture content glue will be very slow to set even if the rest of the considerations don't result in failure. It gets very hot in SC. Find some dry place that gets sun and no rain. Attic, loft of garage, inside a seldom used van, neighbors greenhouse....get creative. A few sunny days in one of these locations and good air circulations and you will be down in the 10% range that will be acceptable for framing components. Doors are another case. You better find some way to get the lumber dry for doors or they will warp upon drying further this winter. One of the above suggested drying environments may do the job. I have dried lumber to 5% here in TN in a barn loft next to the roof. It gets 120-130 degrees up there on a sunny day in July.

[John TenEyck]

What Bill said. The EMC in South Carolina is probably at least 13% right now. I actually find it astonishing that the MC of the wood is not higher than that if it sat outside and uncovered, since it never gets below about 12% here in NY even covered. There are many folks who regularly work wood at 12 - 14% MC and they claim they have no issues with it as long as they plan for what the final MC will be. Anyone right now in the Eastern half of the US who buys KD wood and then puts in their uncontrolled shop is probably using wood at 9 - 12% MC right now, whether they know it or not.

John

[Lynn Reid]

Thanks for the info. Out of curiosity I checked lumber that has been in my shop for awhile...most of it is around 7-9%. My shop is air conditioned and heated. Odd thing was that BB plywood was 11% and it has been in the shop for more than a year. Anyway...I cut the stiles and rails oversized and stickered them with a fan blowing on them. I think I will stick them in the attic though for a short while...I am glad I read that...I was thinking of making a small hot box. Now I am more concerned with the raised panels...if I use them...they will be significantly larger. I don't have any space to put all the lumber inside my shop...it's only 16X24...I do have a covered porch though and thats where the remainder is now.I have milled 25 pieces 7/8 X 21/4 X 36...any of you have a guess how long that would take to get below 10% in a hot attic? I need to finish these cabinets as soon as possible! Thanks! By the way...these will be kitchen cabinets.
Lynn
Lynn

[bill tindall]

Hot and with good air circulation you can loose several per cent per day. In any case you are talking days not weeks. As far as the BB, don't take moisture meter readings too literally. The various principals that they depend on to measure all depend on what the substrate is. When one wants the correct number the only way to get it is to oven dry and measure weight loss. Dry to constant weight at 220F. Weight loss divided by final weight x 100 is the true percent moisture. If 10% or less I would not hesitate to use it after a few days of equilibration in the shop. You can stick the panel parts in the attic and they will be dry enough in a few days. It should not be difficult to get the rough cut pieces in some place to get them hot and dry.

[Scott T Smith]

Lynn, 4/4 spalted maple should acclimate in about a week or two in your hot attic. I'm with Danny; I would suggest that you dry below 10%. I would strongly advise you to sterilize the lumber too; if your attic routinely gets above 135 degrees for a few hours you can sterilize it up there.

Per my kiln operators manual,

At 75 degrees, and 50% relative humidity, the EMC of wood in a house will be about 9%.
At 75 degrees, and 40% RH, the EMC will be about 7.7%

Regarding your BB plywood, you don't mention what type of meter that you're using but the most accurate meters have adjustments built in for temperature and species. Unless yours has the ability to enter corrections for these factors, the readings can and will vary by a few percent between different species / thickness of lumber and plywood.

[Lee Schierer]

Question. I have a lot of cherry that has been stickered in my shop for about 10 years. Moisture content still at 10%. I live in SE OH and the boards are only 1" thick. Even if I kiln dry it, won't the moisture content rise once stored back in the shop?

If your shop is in a basement or has an uninsulated floor I would expect the moisture level to be that high. Cherry in my shop was at 7% when I brought it home from the lumber mill and after 3-4 months in my shop it is at 8% in NW PA where the humidity has been unusually high this summer.

[Lynn Reid]

Hi...the moisture meter is nothing fancy...probably came from Rockler or Woodcraft...certainly nothing that measures by species. I put the maple in the attic...I measured again this morning and after one day in the attic the average reading was 11%...one stick on the top was at 8%. I'm thinking about putting all the lumber I just bought up there before it breaks for cooler weather. How to sterilize if the temperature up there doesn't reach 135? Build a tent and fog it with insecticide? Thanks for all your input!

[Lee Schierer]

I would strongly advise you to sterilize the lumber too; if your attic routinely gets above 135 degrees for a few hours you can sterilize it up there.

I'm not sure what you mean by sterilize, but "sterilization" does not occur at 135 degrees. You might kill insects, but that is about all at 135 degrees.

[Scott T Smith]

I'm not sure what you mean by sterilize, but "sterilization" does not occur at 135 degrees. You might kill insects, but that is about all at 135 degrees.

Lee, in the context of a post about lumber moisture content and drying on a woodworking forum, my advice is related to the sterilization of lumber from a woodworking perspective.

For purposes of sterilizing lumber (ie killing common wood-borne insects, larvae, mold spores, fungal stain, etc that may reside within the lumber), the US lumber industry standard for kiln operators is to heat the core of the lumber to 133F (56C) or higher for at least 30 minutes.

See page 145 and 146 of the USDA Forest Products Laboratory Dry Kiln Operators Manual, Chapter 7 (linked below) about kiln schedules and sterilization:

http://www.fpl.fs.fed.us/documnts/us.../chapter07.pdf

Length of time and temperatures vary; it is possible to sterilize lumber at 125F over the course of several days, or 140F for a much shorter period of time. Also time/temps will vary slightly depending upon the MC% of the lumber and a few other, kiln specific items (RH% drying management versus wet/dry bulb management, as well as the kiln drying schedule).

Lumber produced to make pallets that are shipped to European countries requires a different sterilization schedule, and the lumber must be marked/graded accordingly.


Now, in the context of sterilizing surgical instruments for my wife's Veterinary practice, temperatures in the autoclaves are much higher.... but then again this isn't a medical forum!


Lynn, I would advise against fogging your lumber, for a variety of factors. You can build a simple sterilization chamber out of foam board and a space heater and sterilize in your shop. I you send me a PM with your e-mail address, I'll be happy to send you a copy of an article that appeared in FWW a year or two about about this same topic.