# Humidity and Warping



## Jeff86 (Apr 13, 2012)

Hi everyone,
I am a high school woodworking teacher and I am looking for some advice regarding my shop. I am in my third year at this shop, when I first arrived I noticed that any lumber I brought in would warp badly. Both hardwood and softwood. I bought a hygrometer and noticed that as soon as the heat gets turned on in the fall, relative humidity in the shop drops well below 30% (as low as 10% at times, its 22% right now). So the majority of the school year has these conditions. I have tried stacking lumber with stickers(spacers) and even strapping every 12 inches, it still seems to want to warp badly. I even get warping on old furniture that we bring in to refinish. Shop is approx. 50' x 50' with very high, angled ceilings with virtually no insulation, cinder block walls. New England climate. Any advice/information would help at this point. Could lack of humidity be to blame? 
Thanks
Jeff


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## wmodavis (Aug 28, 2007)

Absolutely low humidity can be to blame.

If the relative humidity is below what the equilibrium relative humidity of the wood as received, the wood will loose moisture to the surrounding air. As that happens the wood fibers shrink causing checking, warping, cupping and other defects to occur.

Besides the hygrometer you need a wood moisture meter.


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## oldworld124 (Mar 2, 2008)

Stand the wood vertically but not touching each other. I will try to post a photo of how to do it. The wood will be more stable this way. It will also have less checking on the ends. You need to keep the wood away from any direct moving warm air.


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## davidmicraig (Nov 21, 2009)

Is there anyway that a humidifier could be brought in to use during the winter months? I would think cost could be justified in comparison to the lumber lost due to the environment in the room.


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## killerb (Nov 1, 2011)

I would check the moisture content of your wood. It sounds like it is way to wet when you get it. I am in Wisconsin and we get your winters also. I build furniture and sell lumber, it sounds like whomever is selling you lumber is giving you wet stock. It could move some in the winter, but good kiln dried stock should never do what you are saying. Hope this helps. bob


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## Porosky (Mar 10, 2009)

agreed killerb. I just dead pack my stock flat on the floor.. maybe throw some heavier pieces on top.. Properly dried lumber is key.. I do try, not to shock my shop with sudden spikes in temperature.. cool in the summer, just warm enough in the winter.


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## oluf (Jan 29, 2010)

Warping is caused by changes in moisture. Is it possable that the heat is turned down or off at night or during the weekends. Ths would cause the moisture to be changing all the time.


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## fussy (Jan 18, 2010)

As killer said, check the mc of your wood. It's wet and drying too quickly and unevenly.

Steve


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## SnowyRiver (Nov 14, 2008)

I agree with killerb too. It sounds like the wood ihas a high moister content when you bring it into the shop.


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## Jeff86 (Apr 13, 2012)

I've tried buying wood from a wholesaler, a local lumber yard, and home depot, all with the same results=bad warping. I've tried strapping down the lumber and it still wants to warp badly. I have a moisture meter and most lumber coming in is 7-8% (which I think is normal). After a few months in the shop a lot of it is down to reading 0%. I bought a "whole house" 2500 sq ft humidifier from home depot and tried running it but it didn't seem to even make a dent in the humidity level of the room. Like you guys I still don't understand why I'm getting so much warping in the first place.


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## wee3 (Mar 6, 2012)

Interesting info,good luck with a solution.


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## Tomj (Nov 18, 2011)

Buy a humidifier and try to keep the room or where ever the wood is stored at 50% relative humidity. A humidity meter and a scale is really all you need when drying really thick wood but a moisture meter is valuable for lumber though a moisture meter will only tell you the moisture content for as far as the pins go into the wood. I build bows and when drying lumber/staves I can accurately know when my wood is dry and at what moisture content by monitoring the humidity keeping it at a certain level and weighing my wood until it hasn't lost any weight for 20% of the time its been drying. Keeping wood at 40% humidity, 80 degrees I know my wood will end up at around 8-9%, by keeping the humidity at 50% and temp at 80 degrees I know my wood will end up at about 9-10% moisture content. I have to do it this way because a moisture meter will not tell me the moisture content deep in the wood which can play havoc when building a bow of wood that is either to dry or to wet. I dry all my staves in a hot box (just a 8ft by 2ft high coffin type box that generates heat by clear 100 watt bulbs on a dimmer and thermostat) this is extreme for just drying lumber but you can achieve the same with keeping a dehumidifier or humidifier along with a humidity meter and a thermometer near where you store your wood and keep it at 50% humidity. I don't use a humidifier, I was able to raise the humidity by putting buckets of water in the hot box. Even a small dehumidifier would have been overkill for such a small place though I might have to buy one for some of the other places I store my lumber. Good luck.


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## Loren (May 30, 2008)

Use a humidifier. Forced heating is making your shop unusable.

You might try to get the school to spring for the materials to build
a wood storage room perhaps divided in half so you could bring
the wood to shop humidity slower using humidifiers.

Still, the shop is clearly way too dry and needs humidification.

This whole aspect of working with natural materials would be 
most instructive to the students to see firsthand. They can
learn about techniques and machinery from many sources,
but you have a valuable teaching opportunity in this specific
and difficult-to-grasp aspect of woodworking. It is fundamental
to industrial woodworking and wood technology: the science
of wood.


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## DIYaholic (Jan 28, 2011)

I certainly can't help solve your problem, but am thankfull that you posted your problem.

I was wondering what relative humidity level to shoot for in my basement shop. From reading this 50% sounds about right. I also have a wood moister meter to monitor wood stocks.

Thanks for posting, as it also help me, in the setup of my basement shop.


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## Tomj (Nov 18, 2011)

The only thing is "DIYaholic" and I'm not sure how much this matters when building furniture is some woods perform better at different moisture content, Hickory for instance will perform better in a drier climate meaning it will be stronger in tension and compression in lower humidity. Another wood well known for being used for bows Osage Orange will perform better in a little higher humidity at a equilibrium moisture content of 9%.


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