Replies

1. 
   SgianDubh | Jul 11, 2008 10:44am | #1

   It depends on what you're trying to produce in your workshop. You've also posed one of those questions where there are no hard and fast rules.

   However, you state that the humidity in your workshop hovers around 40% and above. I assume you mean the relative humidity. You don't say what the upper number is. Nor do you say what sort of typical daily, weekly or monthly cycle you experience.

   Anyway, be that as it may, 40%RH maintained for significant periods means wood heads towards about 7% moisture content (MC). 60%RH, sustained for a long enough period equates to approximately 11.5% MC in wood. 80% RH = roughly 16% wood EMC (equilibrium moisture content). But at every RH figure I've mentioned the wood needs time to reach the EMC or MC numbers I've given. 

   So, if you're buying kiln dried wood, dried to US standards, you'll be buying stuff that is kilned to 7% MC. Note that that figures also ties in with the 40% RH number you mentioned in your question. If your workshop cycles from about 40% RH to about 60% RH during a typical year that happens to closely match the typical RH range of most houses that have good insulation and climate control. So in that scenario your pretty well set up using kiln dried timber to make furniture for indoor use in your workshop.

   If, on the other hand, you like to mostly make wooden artefacts for external use then you should bear in mind that most wood used outside tends to hover between about  16% MC and perhaps 22% MC, or at least it does here in the UK. I'm not sure about Tennessee typical annual weather conditions, but if you were in Arizona I'd expect those numbers to be substantially lower, eg, perhaps somewhere between about 7% and 13 or 14% MC. So, given the scenario described in this paragraph you'd probably come to the conclusion that using kiln dried wood and making furniture for outside use in your workshop might not be the best match. You'd probably want to use air dried wood that doesn't get as dry in the first place.

   In order to keep this post reasonably short I'll leave it at that, but I could go on for several pages on the subject of wood, relative humidity, absolute humidity, temperature, moisture gradients and so on, but that might be too much information, ha, ha. Slainte.

   Richard Jones Furniture

1. 
   Hambone | Jul 12, 2008 02:57am | #3

   Thanks SqianDubh !!  obviously you are very knowledable on this subject and according to you I don't have a problem, especially sinse I bought a dehumidifier for the shop. Thanks again.  Gerald.   (Hambone).

2. 
   dkellernc | Jul 11, 2008 06:12pm | #2

   Hambone - As a point of reference, I live in Raleigh, NC, and we have very similar climates.  My shop is in the basement, so it stays a little damper during the winter than it would if it were in a separate building.  To prevent my tools from rusting in the humid summer, part of my house AC is directed to the basement, and I've installed a low-temp dehumidifier.

   The dehumdifier is set so the shop is consistently held at 51%-53% relative humidity during the summer, and varies between 38%-42% in the winter.

   Generally, I've had no issues with any of the furniture I've built that's been subsequently placed in someone else's home, though most of these pieces have gone to homes also in the Southern US.  I'd attribute some of that to avoiding cross-grain construction.

   Regarding working stock in a shop, my thought is that consistency in humidity is far more important than the actual value, provided it's not at the extremes (i.e., 10% or 80%). 

1. 
   Hambone | Jul 12, 2008 03:05am | #4

   Thanks for your responce Dkellernc!!  I don't think that I will have any more problems with rust.  I was tired of having to constantly clean and wax my table tops because my health isn't as good as it use to be, now I can spend more time in actual woodworking...  Thanks for your again for your responce.    Gerald  (Hambone)

1. 
   coolbreeze | Jul 12, 2008 05:45am | #5

   40 percent RH????

   Here in south Mississippi the humidity is sometimes double that. On a few occasions, the RH was so high that I had to run the catfish out of my vegetable garden:-)

1. 
   Hambone | Jul 12, 2008 04:36pm | #6

   Hello coolbreeze,  Thanks for your responce!  I was wondering where the Lions club got all those catfish that they were serving at the " Dave Macon Days " (A musical celebration) this weekend. Darn good catfish!  Gerald.

2. 
   dkellernc | Jul 12, 2008 05:54pm | #7

   Gerald - It's worth buying one of those mini battery powered "weather stations" from Radio Shack and put it on your shop wall.  Most of these are under $15 and will display both RH and temp, and also include a facility for recording both the min/max of each of these readings.  That's quite handy for figuring out where to set your dehumidifier to optimize humidity control and power usage.

   Most dehumidifiers have a "normal" "dry" "very dry" and "continuous run" setting, which ain't too helpful in knowing what the actual humidity is.  With the aid of the Radio Shack meter on the opposite wall of my shop, I was able to determine that "dry" would keep the shop at about %50 R.H., which is enough to keep the tools from rusting (that seems to happen with Relative Humidities in excess of %60) without blowing out the power bill.

   If you're going to buy a dehumdifier, make certain that you buy one that's a low-temp model specifically made for basements.  Even though your shop might not be in a basement, you still want the low-temp operation, because it has a defrost cycle that prevents the coils from icing up.  It's a real drag to have a spate of rainy weather in the fall or spring when the temp is in the 60's and your dehumidifier ices up after 15 minutes of operation.

   David

3. 
   saschafer | Jul 12, 2008 07:30pm | #8

   Just as a general rule of thumb, if you can keep the relative humidity of your wood storage in the 40-50% range, you're in good shape for almost anything, unless the things you make are expected to end up in places with extreme humidity conditions (either very low or very high).

   -Steve

4. 
   knuts | Jul 13, 2008 03:22am | #9

   I'm in Raleigh too, and I run a small fan 24/7 to keep the humidity under control.

5. 
   Tinkerer3 | Jul 13, 2008 06:59am | #10

   Here in West Virginia the RH probably runs about the same as in your area.  My shop will run about 30% to 40% in the winter with inside temperatures of 65° to 70°.  I run the dehumidifier in the summer when the outside temps are above sixty and regulate the RH to 48% to 52%.  If I don't have the dehumidifier on the RH will stay about 70% to 80%.  I don't know if those Rhs are desired or not but it seems to control the rust.  Last summer, I didn't have a dehumidifier in the basement.  It stayed around 70° with a 70% RH and got a lot of mold.

1. 
   Hambone | Jul 15, 2008 06:55pm | #11

   Thanks to ALL who responded to me on this subject.  I now have a better understanding of it and you were all very helpfull.  This was my thoughts, " RELITIVE" humidity??!! What is it relative to? The dictionary says:  1. Connected; 2. considered in comparison to relationship with something else. RELAITVE to what?  The to the amount of rain that we've had?  The temperature?  And how does it effect my wood working? As it turned out I don't have a problem. Especially since I put in a de-humidifier and left a fan going whenever I think that the humidity is getting to high.   Thanks again to all  Geralg.

1. 
   dkellernc | Jul 15, 2008 07:04pm | #12

   What's important here is consistency.  A fluctuating relative humidity will result in wood movement (cupping, twisting, expansion/contraction in width, etc...) that lasts for several days to weeks after the change.

   From the technical standpoint, relative humidity is "relative" to the saturation point of water in the air at a given temperature.  It can be calculated from the absolute humidity (which is a measure of the mass of water per mass of air) and the temperature by means of something called a "psychometric chart", which displays the relationship between the air temperature, the absolute humidity, relative humidity, and the dew point at a given atmospheric pressure.

   But you don't need to know all of that technical stuff.  What you're interested in is the relative humidity.  At a higher relative humidity (expressed as a percentage, with 100% equaling the saturation point of water in the air at that temperature), wood will have a higher equilibrium moisture content, and at a lower relative humidity, it will have a lower equilibrium moisture content.

   This re-equilibration of wood's moisture content occurs whether or not the wood's been "dried" in a kiln, and because wood expands when it absorbs water and contracts when it loses water, you want to keep its moisture content pretty close to constant.

1. 
   Tinkerer3 | Jul 16, 2008 05:54am | #14

   Very well said.  I think one of the other aspects of RH in relation to a wood shop is the affect of a high RH to rust on tools and equipment.  I'm not too sure what the breaking point is but holding it to below 50% seems to help a lot.

1. 
   dkellernc | Jul 16, 2008 04:26pm | #15

   I agree - I found significant light surface rust on my Lie-Nielsen and Stanley handplanes when the shop humidity went over about 60%.  I hate rust, but I hate "polishing" tools even more.  The breaking point on buying the de-humidifier and paying the extra $$$ on the power bill came when I found a light coating of rust on a couple of antique Norris planes - that was completely unacceptable.

   I don't doubt that there would still be a light surface coating of rust on the steel portions of my tools if my shop was left unattended for the next 10 years at 55% R.H., but there seems to be no problem at that humidity level and with occasional wiping with 3 in 1 oil.

2. 
   Tinkerer3 | Jul 17, 2008 05:24am | #16

   For the small tools that you are talking about, you might place them in a cabinet with a small light.  It would take very heat to lower the humidity a great amount and if the heat is contained in a cabinet it wouldn't be uncomfortable in the room.  My problem is more big iron, thought I do have some small tools also.  You just can't containerize the big tools.

3. 
   dkellernc | Jul 17, 2008 04:57pm | #17

   Indeed.  I was finding corrosion on the tops of my table saw and jointer as well as my handplanes.  Lapping the sides and sole of handplane is easy, if a bit tedious, but re-flattening a table saw table or a jointer is beyond my capabilities.  The dehumidifier and some regular maintenance with Butcher's Bowling Alley wax was a lot cheaper.

6. 
   WillGeorge | Jul 16, 2008 03:13am | #13

   Illinois here.. I GAVE UP on working in my shop.. AND I waited all winter!

   Wood moving all over the place.. I work in a old garage without any air conditioning...