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Ken W
06-13-2010, 07:41 PM
I've been watching the relative humidity rise in my shop over the past few days as we've been pounded with some heavy rain and I'm wondering how (or if) you all monitor or regulate the humidity in your shop. I've heard that building at 50% would be ideal because it would limit the wood movement as the instrument moves toward either extreme but I haven't seen much on this issue in the forum. Thoughts?

Bradford
06-13-2010, 08:35 PM
I'm on the Oregon coast and this time of year the rH is running 65 to 70%. I run a dehumidifier in my shop to bring the rH down to 45%. As I sell my instruments all over the world, it is vital that I do so. Any instrument built in a humid environment and sent to a dry one is very likely to crack. Some builders are lucky enough to live in a climate where humidity control is not necessary, some consider an acceptable range to be between 40 to 55%.

Brad

Allen
06-13-2010, 08:49 PM
Monitoring the RH and if necessary controlling it is absolutely critical to building a quality instrument. Building between 40 and 50% is considered the norm, with most favouring the lower range. I build right on 40% RH. Monitored with several high quality hygrometers. The digital ones you can buy may or may not be accurate to start off with, and they tend to loose accuracy with age.

Depending on your environment, you may need to add, or remove moisture from the air. In my case living in the tropics, its never too dry, so I only need a de-humidifier. Though a couple of luthiers only 4 hours from me will have to add moisture, or remove it depending on the way the wind is blowing. Either from the hot dry outback, or from the wet Coral Sea.

Building at around 40% RH for most people is considered ideal because when wood gains moisture from being in a more humid environment, it swells and top and back plates take on a greater dome. Nothing catastrophic other than the action might get a little high. However if it goes down below what the top and backs were braced at then the wood is going to shrink, and the top and back will go concave. Lowering the action. And if the RH is 10% or less and this happens too quickly, the result is more often than not a split in a top or back.

Some people are lucky and live in areas that have a fairly stable relative humidity, so they really never run into problems, but many have swings of 60 - 80 % and it's going to cause the builder all kinds of grief in those situations.

Hope that was of some help.

Matt Clara
06-14-2010, 03:39 AM
Building at around 40% RH for most people is considered ideal because when wood gains moisture from being in a more humid environment, it swells and top and back plates take on a greater dome. Nothing catastrophic other than the action might get a little high. However if it goes down below what the top and backs were braced at then the wood is going to shrink, and the top and back will go concave. Lowering the action. And if the RH is 10% or less and this happens too quickly, the result is more often than not a split in a top or back.

Interesting, Allen. Humidity is quite high here in Michigan right now (some areas reporting 100%, but it's only 88% here in Lansing). I did some cleaning up in my shop area over the weekend and picked up the first uke I built last winter, and noticed it has a pronounced (noticeable, anyway) dome to it. I built it flat. I looked inside, and everything appears to be holding together just fine.

(I should add--my dehumidifier packed it in this summer. I just ordered a well reviewed Frigidaire off of Amazon with super saving shipping (free shipping).)

Pete Howlett
06-14-2010, 03:39 AM
Kevin Hall the Canadian builder made a very astute observation: Condition you wood in a drying room. Store all your work there and glue up in that 'climate'.

I tend to keep all of my work in my house - the ultimate place where it will rest and resisit shipping to Arizone or Belize :) and my workshop fluctuates between 45% and 55% with my conditionaing room at 50%. I'm not too paranoid if their is a blip dues to climates changes as long as my wood and work are stored in a 'controlled' way. The Uk has a temperate climate so pushing the RH down is something I have to do in my workshop with 2 humidifiers working daily...

fahrner
06-14-2010, 03:44 PM
Two relevant links (Kinda). The first is from Timberline Guitars and the second is an interview with kevin Hall (Pete's reference above). The second perhaps not as relevant to this topic but I just found it very interesting and ties in to Pete's comment.
http://www.timberlineguitars.com/Pages/humiditymatters.htm
http://www.guitarbench.com/2009/06/03/kevin-hall-luthier-interview/

Moore Bettah Ukuleles
06-14-2010, 04:48 PM
Although I have a dehumidifier (two actually) I don't really like to use it. Gives off more heat that what is comfortable for me. My clean room, the room I build in and where all of my wood is stored, is on the small side 8' X 16') so I find that a small room A/C is idea in removing moisture and controlling the temperate I like (70 degrees and 45% RH). In fact the A/C does a better job in lowering the humidity than the humidifier does.
I'm glad the topic came up. Building in a climate controlled environment is probably the most important any single thing you can do. Without it, your wood selection, your bracing patterns, what kind of glue you use, how many routers to buy.........none of that is important if your instruments aren't going to last or will be constantly changing. If you are building for yourself and don't have the resources to build in a CC room, there are some things you can do to help cut your losses. If the humidity is high in your area, these include assembling, gluing up plates and braces, etc during the driest times of the day and never build when it raining outside. When you are finished with a procedure, throw your work in a dry box. This can be a closet, and old refrigerator, a large box, that is constructed or modified with a light bulb, small fan, etc. Keep it warm, not too warm, and keep the air flowing. Eva-Dry is a small closet dehumidifier you can find at Ace Hardware for about $50. It's small, quiet and works pretty well.

Ken W
06-14-2010, 04:59 PM
I appreciate the thoughts shared here. Chuck's suggestion about a dry box reminded me that when I worked in a welding shop we used to keep our welding rods for the stick (arc) welders in an old refridgerator. It didn't work, wasn't even plugged in, but because it was sealed it would keep moisture from soaking into the flux coating on the rod. I haven't given that a thought in terms of keeping wood dry through the muggy days of July and August but it might be worth a try.