I will be woodworking in my unheated garage throughout the year, in Victoria BC, Canada. The winters are cold and damp, and the summers are hot and dry. I am wondering what time of year to expect wood to shrink, and when to expand. Does expansion/contraction in wood only occur due to moisture, or does the temperature effect it as well? Thanks
jim
Replies
Wood movement is a function or moisture, not temperature. I don't know about your area, but when the seasonal relative humidity is low, the wood will shrink. When the relative humidity is high, the wood will expand.
For the amount of movement, go to http://www.woodbin.com, click on "on-line" calculators and then on "Shrinkulator". Input the species, range of seasonal relative humidity and the starting width. The output will be the amount of expansion/contraction.
"Wood movement is a function or moisture, not temperature"
In general terms I agree Howard, but there is a relationship between RH, temperature and wood MC. If you subject a piece of wood that represents the average of all wood species to an RH of 50% at 20ºC for a long enough time it will eventually reach an EMC of ~9.5%. At 15ºC and 50% RH, it will reach an EMC of ~10%. At 25ºC and 50% RH it will reach an ~EMC of 9%.
Similarly, expose the same representative piece of wood to an RH of 50% at 60ºC it will reach approximately 8% MC. And sticking with 50% RH as the constant but now with 80ºC as the temperature it will eventually reach about 6.5%MC.
Kiln drying operations use the relationship between RH and temperature to dry wood. It's quite clear that higher temperatures at any given RH value results in lower wood MC. In the examples I've given there is a resultant difference in final wood MC of approximately 3.5%.
I'll not deny that I'm being pedantic and striving for accuracy. In most cases the difference in wood MC at 'comfortable' temperatures eg, between about 10ºC and roughly 25ºC are quite small, but the relationship certainly does exist. Perhaps I'm being unfair as your answer was of course useful to the the original poster. It gave enough information to send them on their way better informed, and I suspect you know all about the stuff I've just written and didn't want to confuse the questioner with too much information. Slainte.Richard Jones Furniture
Temperature doesn't directly affect the dimensions of wood, wood doesn't expand and contract in response to temperature the way metal does.
While you describe the summers in Victoria as hot and dry, I suspect that the summertime relative humidity there must at least be moderate since the city is surrounded by water.
The wintertime relative humidity in your unheated shop is probably in the same general range as the summertime relative humidity, so there wouldn't be a lot of wood movement between winter and summer if the piece never went indoors.
You will most likely have moderate shrinkage of wood going from either your winter shop conditions, or summertime conditions, to the piece being indoors in your home in the winter. In a home in your climate the relative humidity indoors is typically lower because of the heat being on which drops the relative humidity unless you actively humidify the house.
John White
I am in Vancouver. I used to store wood in an unheated detached garage. After it had been raining for several cold winter days (weeks?!) in a row, I would get humidity readings of 90% or more at 5 degrees C. In the summer it would get down to 40% at temps of 25 degrees C. Granted, my garage was also quite poorly sealed!
If your garage is better sealed it might not get so extreme, and you might be able to take the edge off the winter humidity with a dehumidifier.
Dan
Jim, my abode is on an island just west of Seattle, so not far from you at all. Cannot imagine working in an unheated space for much of the winter. We had 2 or 3 weeks recently that barely made it close to 40° and the nights were in the 20's. Any chance you can get some heat in there somehow??
My unheated shop is in Vancouver, where the temperature has been sitting around 0-6 degrees Celsius for the past while. All my visitors comment on how the shop is "freezing". I stay busy and keep moving and never find it cold. I have a small ceiling-hung heater which I never use.
So my unheated shop increases productivity in two ways - less visitors for anything more than a hello, and an incentive to keep busy!
Chris @ flairwoodworks
- Success is not the key to happines. Happiness is the key to success. If you love what you are doing, you will be successful. - Albert Schweitzer
Edited 2/10/2008 1:56 pm by flairwoodworks
I simply don't function in that temperature range! With the horses, if I'm riding I'm OK, but as soon as I get off and am just locomoting on my own, I get miserable (dressage is very hard physical work, gets the blood pumping). So if I try to do shop work in that kind of temperature, it's a lost cause.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
I find it hard some days to get motivated to work when the tem is near freezing but I have little choice for the time being. Once I get working for 10 minutes or so, I get warm enough to work. Thanks for all the responses.jim
MY SHOP is in Vancouver as well, if your garage is insulted & or sealed well your wo0d movment should be less ,as well as keeping that nasty mosture we have off the tools. rust is from moisture and not so much cold as well
Edited 2/16/2008 12:35 pm ET by woodguydan
I mill and airdry both softwood and hardwood lumber just across the ditch from you.
In dense hardwoods like Garry Oak, Bigleaf Maple and Pacific Madrone stacked outdoors you can expect a high of 18% MC by the end of December dropping to a low of 8-12% in summer depending on how dry the summer is.
In unheated covered and enclosed storage like my unheated shop, the swings will run from around 8-15%.
Less dense woods like Red Alder, Western Red Cedar and Doug Fir have smaller moisture swings.
Wood used for household furniture needs to be stabilized at 9% or lower here before use. That usually means stacking your winter supply behind doors in the house before the rains commence.
On Hood Canal I may have larger swings than y'all on the edge of the Olympic rain shadow. We get 60" of rain annually from October to May with attendant 100% humidity, you get less than that.
Temperature affects relative humidity and relative humidity affects vapour pressure. Low temps increase relative humidity and that increases vapour pressure. Higher vapour pressure increases the takeup of moisture by wood.
I'm about 80k up the Island from you and have had a homemade device that gives me a clearer picture up on the wall in my semi-heated shop for better than ten years. It's a 1/4" thick cross grain slice of a 3/4" by 12" wide oak plank with one end anchored and the other connected by a pin to the short lever arm of a pivoting pointer. The pointer tracks through about 45 degrees of arc according to the takeup and release of moisture by the oak strip. I marked the travel for the first couple of years to establish the range and now have a quick reference to current conditions and how they relate to previous seasons.
I'd have to go check the markings for seasonal change to be precise about the timing of the changes, but basically, winter conditions here cause wood expansion and summer conditions cause contraction.
I'll see if I can get a reasonable photo of the markings I've made to give you a better guide.
Here are the pictures. First one is the marked readings. Far left marking is mid-February, far right is mid-August. Difference in readings represents about 1/8" change in approximate 12" length of crossgrain oak strip.Second is the gauge itself just to clarify how the marks were arrived at. Pointer is about 4" long. The pin on which the pointer is mounted is about 1/4" below the pin that connects the strip to the short lever arm of the pointer. The strip is fastened to the backing board at the left end only.
Edited 2/18/2008 1:42 am by observer
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