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mikeyb2
09-25-2016, 12:47 AM
I'm waiting to glue up some braces(top and back), but the humidity is way too high (70+%) and doesn't look like it will come down anytime soon. I work in an open garage and wooden shed, so it can't be controlled.
Is there any simple and reliable way of drying the wood enough to allow gluing to take place? And how would I know when it is dry enough?
I think someone on a previous post suggested putting it in the oven for a time, but I don't fancy that idea. Thanks Mike.

greenscoe
09-25-2016, 01:02 AM
I bring things into the house (kitchen) to glue or finish.......but then I don't have a wife to chase me out of the kitchen! I also store timber literally under the bed not in the workshop. In winter this is better for me and the wood.

Wildestcat
09-25-2016, 01:39 AM
Hi Mike. I have insulated and draught proofed my attached garage such that I can run a small dehumidifier unit and maintain relative humidity at 50% to 55% when I need to. These days I run it most of the time. Power consumption is pretty low, so not a huge cost. I also added a small radiator fed from the house heating system! However if that approach isn't feasible, then for wood storage a luthier friend of mine recommends buying a cheap 2nd hand wardrobe or similar large cupboard, sealing it to minimise air movements and then install a small dehumidifier in the bottom section.

mikeyb2
09-25-2016, 02:41 AM
Thanks Greenscoe, but humidity in the house is 65 at this moment, even though I too have no wife to chase me out. I'm going to have to look into adapting Paul's idea , and make a sort of box with a dehumidifier inside. Cheers both of you.

Timbuck
09-25-2016, 03:20 AM
It's not the moisture in the air you have to worry about..it's the moisture in the wood..the idea is that all the pieces of wood and the air have the same ambient moisture content when they are glued together, and remember thicker sections of wood like necks and blocks take longer to lose or gain moisture, also different species of wood have different expansion and contraction levels when absorbing or losing water, as I've noticed on several old Island style ukes, where the Koa has shrunk across the grain more than the spruce braces have shrunk lengthwise, resulting in the ends of the braces sticking out of the sides of the uke body... Another thing to think about is! you can have all the pieces and the air at the same humidity and then you glue them together with a water based glue like hide glue or Titebond and you are putting moisture back in again :eek:..I remember Rick Turner of "Renaissance Guitars" overcoming this problem on necks warping by using epoxy glue for the fretboards.

So making a humidity controlled box for the components seems to me like good idea.

Michael N.
09-25-2016, 03:26 AM
Thanks Greenscoe, but humidity in the house is 65 at this moment, even though I too have no wife to chase me out. I'm going to have to look into adapting Paul's idea , and make a sort of box with a dehumidifier inside. Cheers both of you.

You need a cabinet/wardrobe. You can buy small wardrobe dehumidifiers or mount a couple of light bulbs inside the cabinet. You need around 30 to 50 watts of 'heat'.
The higher temperature will lower the humidity and of course the dehumidifier will do the same.
You then 'condition' the pieces of wood inside the cabinet. With tops, backs and braces the wood is so thin that it will condition in a matter of 3 or 4 hours. Take the wood out, glue and place it all back in the cabinet again. No need to rush. 20 minutes outside the cabinet isn't going to cause any problems. I don't even put it back inside the cabinet, most glues you can take the clamps off after an hour. You will need an accurate hygrometer to monitor the humidity inside the cabinet. You also need to watch the heat.

Kevs-the-name
09-25-2016, 03:46 AM
You need a cabinet/wardrobe. You can buy small wardrobe dehumidifiers or mount a couple of light bulbs inside the cabinet. You need around 30 to 50 watts of 'heat'.
The higher temperature will lower the humidity and of course the dehumidifier will do the same.
You then 'condition' the pieces of wood inside the cabinet. With tops, backs and braces the wood is so thin that it will condition in a matter of 3 or 4 hours. Take the wood out, glue and place it all back in the cabinet again. No need to rush. 20 minutes outside the cabinet isn't going to cause any problems. I don't even put it back inside the cabinet, most glues you can take the clamps off after an hour. You will need an accurate hygrometer to monitor the humidity inside the cabinet. You also need to watch the heat.


I find this really confusing.
If you are always storing wood in a tightly controlled environment, only removing the pieces to glue etc. At which point can you take it out and leave it out?

Michael N.
09-25-2016, 04:43 AM
I don't really understand the question but if you want to build for eg. 50% humidity and your workshop is saying 65% RH, you better condition the wood in the cabinet. It's all dependent on your target RH. If you happen to live in a dry place then it's pointless building a ukelele at 50% RH, you might need to build it at 35% RH or 65% RH if you live in a high humidity environment. The 50% RH quote is just an average, nothing magical about it. It's a Goldilocks figure that is deemed to be suitable for most (certainly not all) habitable places on planet earth.
It's low RH that is the problem. Going from 50% to 35% is probably going to be safe for an instrument that has been built at 50%. Going from 50% to 30% or under (especially for a lengthy period) and you've reached danger levels. Going from 50% to 75% is likely to be safe, although it may effect the sound of the instrument.

Michael Smith
09-25-2016, 09:44 AM
I believe it's best to build around 45 percent humidity. People here in California bring me instruments to repair that were built in Hawaii in poorly controlled environments and they are coming apart, frets sticking out and all kinds of problems. I'm not refering to any of the fine builders who post here and are careful about this. The point is the instrument might not stay in a high or low humidity environment and should be built to withstand (as much as possible) swings in either direction.

Also I have begun supplying customers Bovida two way humidity packets for all my builds and instructing purchasers to use them and keep using them. They add humidity to the case and instrument if humidity is too low and remove humidity if too high. They consist of certain salts that want to stay at about 50% humidity. If the packets get hard from drying out you can leave them outside for a night and recharge them a few times. Not in the rain but a moist night.

I see a lot of people that have put strait humidifiers in their cases that were meant for guitar size cases or taken sponges and put them in a bag and poked holes in the bag. They take their instrument to Hawaii in very high humidity and have problems and wonder why their case smells of mold. (NO NO don't do that) Use a two way humidifier like the Bovida (sometimes marketed under Planet Waves)

Allen
09-25-2016, 10:06 AM
It's no good to dry out a top or back in an oven and then brace it up, only to then leave it open to the elements while you go about working on other parts to close up the body. This is a sure way to turn that part into a potato chip shape when the moisture gets back into the parts.

You need to control the humidity of all your parts while it's being assembled. That is until the box is closed up. After that you are pretty much good, and can work without too much concern......extremes either way can still be an issue, but that goes for caring for any instrument.

Some will use a small cabinet with a low wattage light bulb inside to increase the temperature, and this will decrease the RH of the environment. Even adding a small computer fan inside to stir up the air to help the process. They store their building timber and parts inside when not working on them.

As I live in the tropics, I have a dedicated "dry room" that has a commercial dehumidifier running 24/7. Same idea as the smaller box, but several years worth of building timber are stored in there, along with my go-bar deck etc.

mikeyb2
09-25-2016, 11:40 AM
Thanks again everyone. I raised the question because I made the mistake during my first and only complete build to date, of gluing up without considering humidity. The outcome was that the top dipped very slightly and the radius flattened a little on the back, once humidity returned to normal. I'm in the middle of my 2nd build and the box is now closed without issue. This time I glued around 45%, a few weeks ago. It's my 3rd body I'm waiting to glue, so I'll take note of all your suggestions and tomorrow I'll be looking out for a small dehumidifier. Mike

mikeyb2
10-01-2016, 06:29 AM
well I've been experimenting with a large clear plastic storage box with a lid to seal, a hygrometer and a scrap piece of wood the same thickness as a top would be. Also a Unibond moisture absorber. Starting rh is approx, 65%, put wood into box with hygrometer and Moisture absorber, put lid on and spring clamps to hold it down and seal it. I can see the hygrometer through the box wall, and it gradually decreases as the hours pass. Left overnight, it went down to 40%, so I took the wood out and immediatley tested with a pronged moisture meter, which measured 6%. Ideal, I thought, but only 2 minutes later it went to 12%.
Now I know that wood this thin dries along with the RH and only takes a couple of hours or so to reach a reasonable state(if the RH is ok), but I don't really believe it will soak back moisture in 2 minutes, so my thoughts are that the moisture meter only reads the surface of the wood, so that may well return quickly to the previous level, but the centre of the wood is probably dry enough to quickly glue up some braces before the mc goes up again.
I'd be interested in your experiences and thoughts, thanks.

Wildestcat
10-02-2016, 01:05 AM
Hi Mike. I'd be a tiny bit suspicious of the pronged moisture meter - they tend to be targeted for use by surveyors for detecting dampness in houses, where the danger zone is a lot higher than the range you are testing. Did you check the wood moisture before it went into the box and have you tried re-testing every few minutes over a longer period after removal? Unless you have a very expensive meter I wouldn't expect super high accuracy and repeatability down around 6%.
I have a "Protimeter Mini" pronged moisture meter which I obtained second hand, but new would cost around 150. I have checked the calibration is spot on against a 17% standard resistor, then taken a piece of spruce soundboard offcut that has been in my workshop maintained at between 50% & 55% relative humidity for over a year. In that enviroment it is repeatedly reading 6% to 7% moisture on the Protimeter. I have now moved it into my cellar, which with the aid of a dehumidifier I keep at around 75% RH. After 30 minutes the wood is registering 7% to 8%, so a very slight increase of about 0.5%. I'll leave it in the cellar and check again later, but that jump you report from 6% to 12% in 2 minutes looks suspicious to me .... unless the wood simply had not had long enough in the box at the lower humidity.

PS I am not applying the Protimeter calibration correction for Spruce, as it will essentially be the same for both cases. However the temperature difference between workshop & cellar is about 5 C, which from the Protimeter calibration data would be expected to increase the cellar reading by ~0.5% which accounts for most of the change seen so far.

PPS It's now an hour in the cellar and moisture is still reading around 8%

Dan Gleibitz
10-02-2016, 01:21 AM
"Now I know that wood this thin dries along with the RH and only takes a couple of hours or so to reach a reasonable state(if the RH is ok), but I don't really believe it will soak back moisture in 2 minutes, so my thoughts are that the moisture meter only reads the surface of the wood, so that may well return quickly to the previous level, but the centre of the wood is probably dry enough to quickly glue up some braces before the mc goes up again."

Sounds right to me. I don't know much about instrument building so take this with a grain of salt, but my work is in the fire science field. For fine fuels, the rule of thumb is about an hour lag per mm fuel diameter. This applies to twigs etc, which have a higher surface to volume ratio than a flat board, so I'd expect the board to respond slightly more slowly. I reckon you'd be fine for an hour or so.

This applies in both directions. So as you noted, waiting for a brief period of low humidity after several hours of high humidity won't work. I like Allen's idea of a drying box.

mikeyb2
10-02-2016, 02:46 AM
Hi Mike. I'd be a tiny bit suspicious of the pronged moisture meter - they tend to be targeted for use by surveyors for detecting dampness in houses, where the danger zone is a lot higher than the range you are testing. Did you check the wood moisture before it went into the box and have you tried re-testing every few minutes over a longer period after removal? Unless you have a very expensive meter I wouldn't expect super high accuracy and repeatability down around 6%.
I have a "Protimeter Mini" pronged moisture meter which I obtained second hand, but new would cost around 150. I have checked the calibration is spot on against a 17% standard resistor, then taken a piece of spruce soundboard offcut that has been in my workshop maintained at between 50% & 55% relative humidity for over a year. In that enviroment it is repeatedly reading 6% to 7% moisture on the Protimeter. I have now moved it into my cellar, which with the aid of a dehumidifier I keep at around 75% RH. After 30 minutes the wood is registering 7% to 8%, so a very slight increase of about 0.5%. I'll leave it in the cellar and check again later, but that jump you report from 6% to 12% in 2 minutes looks suspicious to me .... unless the wood simply had not had long enough in the box at the lower humidity.

PS I am not applying the Protimeter calibration correction for Spruce, as it will essentially be the same for both cases. However the temperature difference between workshop & cellar is about 5 C, which from the Protimeter calibration data would be expected to increase the cellar reading by ~0.5% which accounts for most of the change seen so far.

PPS It's now an hour in the cellar and moisture is still reading around 8%
Hi Paul, I'm sure my meter isn't super accurate and I'm not relying on it entirely, it's just a guide. The point is, that after the wood has been in 40% humidity for a few hours, it should be dry enough to glue up. I'm happy to hear that your wood increased very slowly as you state above, so by that rule 30 mins gives me enough time to glue up and set. I think I'm going to have to take a chance, as there's no other way I can control RH and the weather doesn't look like changing anytime soon. Thanks for the input. Mike

mikeyb2
10-02-2016, 02:47 AM
"Now I know that wood this thin dries along with the RH and only takes a couple of hours or so to reach a reasonable state(if the RH is ok), but I don't really believe it will soak back moisture in 2 minutes, so my thoughts are that the moisture meter only reads the surface of the wood, so that may well return quickly to the previous level, but the centre of the wood is probably dry enough to quickly glue up some braces before the mc goes up again."

Sounds right to me. I don't know much about instrument building so take this with a grain of salt, but my work is in the fire science field. For fine fuels, the rule of thumb is about an hour lag per mm fuel diameter. This applies to twigs etc, which have a higher surface to volume ratio than a flat board, so I'd expect the board to respond slightly more slowly. I reckon you'd be fine for an hour or so.

This applies in both directions. So as you noted, waiting for a brief period of low humidity after several hours of high humidity won't work. I like Allen's idea of a drying box.

Thanks Dan for the encouraging words. Mike

Wildestcat
10-02-2016, 03:12 AM
Hi Mike. I think you will be OK. It's now over 2 hours since my test piece went from 53% RH to 75% RH, and in that time the measured moisture content has increased from about 6.5% to 9.0%. I'm now interested enough to check it going the other way, so it is back in the workshop where RH has risen slightly to 55%.