Humidity and Moulding Storage

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free2beme

CGF, Certified Grumble Framer
Joined
Mar 21, 2011
Posts
149
Loc
Brookings, SD
Hey Grumblers!

We are doing some remodeling here and are wondering what the ideal humidity percentage would be for moulding storage. I have some verticle storage and some flat storage. Any tips or advice would be greatly appreciated!

I have been seeing some warpage on my flat storage since the weather switched to super dry from the summer's super humid here in the midwest. contemplating closing in my storage and chop area and climate controling it.
 
The problem lies within my chop and storage area being upstairs in a non climate controlled warehouse. It is very humid and hot in the summer time, which doesn't pose a problem, but then in the winter it is bone dry and cool, and just since it has snowed in the last two weeks i have litterally seen my moulding warp. Trying to prevent more warping....
 
Equilibrium Moisture Content (EMC) of wood is dependent mostly on Relative Humidity (RH) and to a much lesser extent, temperature.

Following is a list of EMCs at various RH, at 70 °F:

10% RH = 2.5% EMC
20% RH = 4.2% EMC
30% RH = 5.9% EMC
40% RH = 7.4% EMC
50% RH = 8.9% EMC
60% RH = 10.6% EMC
70% RH = 12.7% EMC
80% RH = 16% EMC

A change in temperature from 30 °F to 100 °F will only change the EMC +/- 1% if the same RH is maintained.

Assuming the wood was properly dried, and the moulding properly stored after production, a RH of 40% is ideal. 30 - 50% is probably a feasible target to shoot for. This is all based on the fact that humans are comfortable at around 35-45% RH, therefore lumber destined for use in living space is dried to 6-8% MC so it doesn't move much.

I will agree with Hugh that stability is important, but you don't want your storage at a constant 10% RH because then when you send the frame home with the customer they will likely have troubles in their 40% RH home. Unless, of course, you both are in Phoenix.

EDIT: should have said that the data presented above is extrapolated from Figure 8, chart M 144 246 on page 9 of STORAGE OF LUMBER, Agriculture Handbook #531 USDA/Forest Service, 1978.
 
Here in Florida we had ours in climate controlled humidity at 47-53% range. Had to use dehumidifiers because the average humidity was 70-100% ( mostly 80-90%) most of the time. Glad I'm retired, don't have to worry with it anymore.
 
free2beme said:
Hey Grumblers!

We are doing some remodeling here and are wondering what the ideal humidity percentage would be for moulding storage. I have some verticle storage and some flat storage. Any tips or advice would be greatly appreciated!

I have been seeing some warpage on my flat storage since the weather switched to super dry from the summer's super humid here in the midwest. contemplating closing in my storage and chop area and climate controling it.
Click to expand...

You should try Alaska for trying to maintain humidity! When it's 35 and 40 below zero outside and the furnace kicks on every 5 min. moisture is hard to come by. My molding comes from the Pacific Northwest, and I can almost watch it take on a new shape when I unwrap it! I actually do not stock any molding to speak of. Everything is ordered once a week, and shipping is then passed on to the customer. I would love to maintain 40 or 50% humidity, but I'm lucky to get 10 or 12%.

One thing that I can do is to leave the molding in the cold, although I'm not sure what that would do to the finish. That at least freezes whatever moisture is within the wood, and it seems to be stable that way. Anyway, if you can maintain something between 40 and 50% I think that would be ideal. Avoiding extreme changes I think is important as well. Products that acclimate slowly seem to be more stable. I was just responding to give you an idea of what people in the far North have to go through. I had to spray the back of a piece of mat board yesterday with distilled water to get it to relax enough to get under the rails on the Wizard. This morning that same mat was curled 2 inches sitting on top of the counter top after drying out overnight. Such fun! I'm careful when I get mat board to make up any space in the storage cabinet with pieces of foam core. As long as the mat board dries out flat, it at least seems to stay that way.

Cheers,

Troy, in Fairbanks where it's warmed up to a balmy -20 below today. -43 below at the airport yesterday. You folks in the lower 48 have it made!
 
I store a lot of molding in a steel barn through Canadian winters and summers. The temperatures range from 95 F to -15F. I have so much of the stuff I can't get some of it into heated quarters. The cheaper junk will show some crazing, but all the quality stuff stays stable. Keep it off the floor, upright, and ventilated, with good support. Twisting, warping, bowing has never been an issue. If it comes straight, it will stay straight.
 
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