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Finishing an air dried stack3/11
I have a stack of 3 year air dried walnut. 300bf (7/8-1", beautiful stuff). I brought the stack in and finish planed and jointed one edge and sawed to a final dimension in November. The stack was measuring 12-13% then and 11-12% now (5 months later). I moved the stack to a heated area this week and have it in a plastic'd off chamber. Heater and fans running about 4 days now up to 94F in the chamber. I checked the wood in several locations with the ligno and am getting 8.5% on all measures. I was going to go get an air conditioner to help pull some moisture out of the chamber, but now it seems foolish if I got 2.5-3.5% in 4 days. Do you guys think it'll dry down to 7% in the next 2 weeks, or is my heat going to be insufficient for the final push? Heater is maxed, but no insulation. The wood was kept very dry in its air dried location under a roof, etc, so I am not too worried about wet spots in the pile. Interestingly, I had one board too many for the chamber and kept it out and labeled it and it, too, is now running at the same 8.5%, so I'm thinking the chamber has less to do with it than the general environment. Thoughts? Thanks.
I should add the new space is a heated area all year, the winter storage was in a garage without insulation.
This is an update to a post from a month ago, so not intended to be an overpost, but sort of an update now that I'm at 8.5%
If the water is coming out of the wood, where is it going? It has to go somewhere. Each 1% MC loss for 300 bf of walnut requires about 1 gallon of water loss.
I suspect you have moisture meter issues. The air dried stack at 12% is normal. But if wood dried so fast with only 94 F heat, we would not need kilns that often run at 160 F. The piece that is not in your room being about the same indicates this same ms meter issue.
You are a wise old owl Gene. I did a battery change and the boards are 9.5%. I didn't like the air dry board reading the same. The air dry board is about 11 still.
I went an rechecked the control and it is running about 9.5 as well. I took several readings instead of trusting one. Do I need to add a/c unit to get it done in 2 weeks?
So, I have tried all sorts of things to push the last 2.5% of water out of the lumber, but nothing seems to be working. I had an air conditioner running, but it didn't condense any water out of the stack. So, I tried a DH and the coils were cold in a hot chamber, but also not condensing any water. I had the temperature inside the stack up to 110F. Is that temperature too low for the final push? Thanks. I just want to build a desk for my wife! When I contacted local kiln operators, I could generate no interest at all in such a small job.
I have built a lot of furniture using air dried walnut & cherry with a moisture content of 10-11%. You just have to allow for the shrinkage that will occur when it drops down to 8-9%. Do a search and you will find the change in dimensions with MC changes. All wood will naturally expand & shrink, you just need to allow for it.
If you cannot get the lumber to dry when the humidity in the kiln is under 30% RH, then the lumber is 6% MC or a bit less. If your moisture meter or other measuring device, if it does not read this low MC, is not working properly. You cannot have 10% MC lumber in a 30% RH condition at room temperature or hotter and not have the lumber dry.
There are indeed some people that use air dried lumber for furniture and allow for shrinkage. However, it is more likely, they have the lumber dry a bit more in the dry shop while storing the wood, or while working with it. In Colonial Williamsburg, for example, they use air dried, but after air drying it then sits in the rafters (warm air rises and warmth lowers the RH) where it dries to a low MC.
Thanks Gene. I am going to test a piece of the wood with the oven or microwave method. I have never done it, but it should be pretty straightforward with a gram scale and a piece of lumber of known size. The mini ligno is behaving a little suspiciously as even with a good battery it is not consistently reading for me. I will report back my findings just for good behavior.
The moisture meter you have will measure the wettest spot alone the pins. So, if you have a dry piece, but it is early morning and there is temporarily higher humidity in the plant, the surface can pick up a wee bit of moisture and this will register on the meter as wetter wood.
As a quick demo, lick the surface or wipe with a wet cloth and then stick. The pins in the wet area. You will see a higher reading even though this small amount of water does not change the MC of the piece.
If you have a small piece of wood, crack it lengthwise to expose the inside. You could rip it too, but a saw makes heat. Then measure the MC inside the lumber at various depths or distances from the original surface.
When doing an oven test, you do need a piece of at least 50 grams and a balance or scale that reads to at least one decimal. The wood should be in the oven for 24 hours or so while at 215 F. The microwave is ok, but keep weighing and then zapping the wood another 30 seconds on need-low power until you get no further weight change.
OK, so here is what I did. I did a microwave test as per Lamb as I did not see Gene's instruction until just now. I only have a scale that weighs to nearest gram, but I used it anyhow. And I used the microwave at 30% power until the net weight stopped dropping for 3 cycles. My final weight was 176 grams. Start weight was 187 grams. Interesting thing about the ligno is it read the oven dry wood at 4.2% MC which is one of the spurious readings it gives me all the time (its zero for a bad reading I assume) , but I can't get any more weight to come out of the samples, so they are oven dry or darn close. I ran them about 3 minutes out of the gun and about 15 cycles of a minute each after and weighed the set each time until the weight stabilized at no change for 3 cycles. So, the final calculation of the MC of the wood would be 6.2% Almost bizarrely low for air dried stack subjected to heat and fans for 2 weeks only, but it is Minnesota winter. It was a top piece; the bottom pieces might be higher MC%.
Ligno readings prior to test 9.5% typical at 100F (edge readings only), control outside of hotbox was also 9.5%, but was at 70F, so the control MC was higher (but I was too ignorant to realize the 2% heat factor). The edge readings were probably not as accurate as an endcut, but I have found them to be close-maybe not anymore for wood that is running below 10% to start.
I shut off the chamber yesterday since it didn't seem like I was pulling any water out of the stack. I checked two boards today and got 6.8% in all cuts (end grain readings), so that is pretty close to my microwave test and pretty close to my correction for heat above. My air dried sample piece is also pretty dry on end cut tests, but running at 8.1-8.5%. That board never went into the hotbox.
I'd say the lumber is dried well enough to use and I was getting some errors in the ligno due to temperature conversions that I forgot about, my edge readings vs endcut readings, and due to the battery issues earlier. I used it before on green lumber and never even worried about any of these things.
If I try to drive more moisture from the samples, I'm guessing I'd be able to get another gram or two or 1%, so I might not be technically oven dry, but it is close. I'd rather not destroy our $1300 microwave in the process, so I could also just run them in the real oven overnite on low and might just for fun.
I guess the only question for the group is does it seem rational that I would have had air dry lumber at 10.5% mc in November in Mn (recall the battery and edge readings might have been causing some error), and then the lumber got planed and sat in the building and came down to 2% mc or 8.5% in Minnesota winter (my control piece reads 8.1 to 8.5%), and bringing it into a 100 degree dry fans climate for a couple weeks dropped it to 6.8-7% and the moisture just went into the plant/space? And would the 7% MC explain why I was unable to drive any more water from the stack at 110F?
Thanks, sorry if I'm an idiot; I don't do this everyday.
I'd say the lumber is ready to use and the reason I can't get moisture out of it anymore is because I'd need to heat it to higher than 110F and don't need to do so.
Thanks Gene. Your wisdom was very helpful to me.
After air drying, did you bring the wood into a heated area?
The best you can do in MN is 12% MC in air drying, even after years. With your short time of air drying, you would not likely reach 12% MC.
A pin moisture meter cannot read accurately under 6.5 %. At 4% MC, you are reading a short circuit in the meter, which is going to affect the higher MC you measure by giving you a false reading...it will act like two resistors in parallel.
I had the stack at 100F for 3 weeks and Mn had a very dry winter with very little snow even.
Between my microwave work showing 6.2% and the meter showing 6.8; I am accepting the lumber as unusually well air dried and picking up 1.5% drying in the ultradry heated atmosphere and heated chamber here now. The logs were many years aged lumber prior to sawing. I am wondering if that has contributed to this strange phenomena as well.
When I processed all the lumber through the planer; I ran white oak and red oak and cherry, so i am going to put them to the meter next week and I'll report back. Many of those logs were aged as well, but not nearly as long as the walnut.