Changing moisture content

[Woodmatt]

Good morning all,
I have some kiln dried Maple and Walnut that has been sitting in my unheated workshop for four months,generally moisture content is around 16% for most stuff in the shop,so my question is how much would the moisture % rise in general after sitting for that length of time and if I bring it indoors roughly how long should I expect it to take to reduce back to 7-9% ?The boards are 1" thick,thank you

 

[Yojevol]

Difficult to say without knowing your house atmospheric conditions. Do you know what the MC was when you got it? How do you know that most of wood is at 16%?
I suppose the quick answer is that it will take a similar amount of time to get back to where it was. However I think you could start using it long before those 4 months have elapsed.
You could take a small sample and determine the present MC by the weighing, heating, weighing method over a few days until there is no more weight loss.
It would then be worth considering an initial cutting/planing exercise before bringing it in for a final drying/resting period. This would allow any movement to manifest itself before working it to it's final dimensions.
Brian

 

[Sgian Dubh]

Interestingly, because of the phenomenon hysteresis, wood adsorbs moisture quicker than it loses it. However, that's not particularly important, but knowing the current moisture content is. As Brian says, you can test for this using the oven drying method, in this case using a microwave. Alternatively, a decent moisture meter should be able to give you reasonably accurate figure to work around. If you're wanting to use this wood for indoor furniture it would certainly be better to be drier, and about 13% MC and below would be okay.

Keeping the wood stickered up in relative humidity (RH) conditions averaging 50% for three or four weeks should bring it down from about 16% MC to 13% MC and below. An average 50% RH condition will eventually result in all wood species settling out at somewhere between about 9.5 - 10.5% MC. Any wood at approximately 20% MC and below is primarily affected by RH conditions to increase or decrease moisture content rather than air movement to remove moisture.

As to how much your wood will gain moisture if left in your workshop is almost certainly impossible for any of us to assess because we don't have a good knowledge of your workshop's conditions, its structure, insulation, and so on. You could buy a relatively inexpensive hygrometer and place it somewhere in your workshop so that you can monitor atmospheric RH, and knowing that would allow you to assess likely MC of your wood. And dead or close stacking of your wood vastly reduces the speed at which wood adsorbs or desorbs moisture.

It's a fairly complex subject that could take a few pages of text and charts, etc, to give you a pretty substantial understanding of all the mechanisms that affect wood MC, ha, ha. Slainte.

 

[profchris]

Any wood which has been in that workshop for months will be at a similar MC to the other wood there.

From experience, a 2mm thick board takes a couple of days to acclimate to indoors from the workshop. So a 24 mm board should take 12 days or so - a couple of weeks.

If I were using that wood, and humidity control was important, then I'd give it three weeks. If really important, I guess I'd even measure its MC

 

[Woodmatt]

Thank you for your replies,I think the general moisture content is around 16% as I did have a moisture meter a while ago and that was a regular reading the machine has since pack up working,I have now ordered a new one so once it arrives I will have a better idea of the current % and depending on what I find I will take all your advice a bring it inside for a period of time and measure the changes on a daily basis until I get down to a usable level,thanks again for the quick replies.

 

[johnnyb]

by no means perfect but common sense says it must be a fact. I have a load of planed beech i brought used in the summer. it was flat. I've stood it in my damp cold store and its cupped. I cut a few feet for a shaker table top then planed it flat and marked it. so one side used to be flat and the other side is flat.
I popped them behind the TV for 3 weeks. checked and they have returned to being flat. and the planed side has cupped. these are 11/2 thick.

 

[Just4Fun]

The question you are asking (long should I expect it to take to reduce back to 7-9% ?) is fine if you need to schedule your work so you know in advance when it will be possible to use the wood. If that is really your situation then that question makes sense.

Personally I take a different approach, because I am a hobbiest who does not need to plan my work in advance. So instead of asking "how long will this wood take to dry?", I ask "is this wood dry enough yet?". To answer that question I accurately weigh a small sample, then weigh it again every few days until the weight is stable. At that point I am ready to use it.

Using this approach I never know, nor need to know, the moisture content of any board. I just know if I can use it or not and that is good enough for me.

 

[Woodmatt]

The question you are asking (long should I expect it to take to reduce back to 7-9% ?) is fine if you need to schedule your work so you know in advance when it will be possible to use the wood. If that is really your situation then that question makes sense.

Personally I take a different approach, because I am a hobbiest who does not need to plan my work in advance. So instead of asking "how long will this wood take to dry?", I ask "is this wood dry enough yet?". To answer that question I accurately weigh a small sample, then weigh it again every few days until the weight is stable. At that point I am ready to use it.

Using this approach I never know, nor need to know, the moisture content of any board. I just know if I can use it or not and that is good enough for me.

Thanks Just4Fun,I like you am a hobbyist so I am in no hurry so your answer is very apt,maybe I need a different approach to my work

 

[AJB Temple]

Whatever you do, the moisture content is going to vary over time. There is no set single point. In the UK typical average relative humidity in summer is around 50-55% (maybe as high as 60% and in winter around 45-50%. Temperature swings in a centrally heated house can also be as much as 10 degrees C through a 24 hour cycle.

For most furniture this range does not matter much, but it plays havoc with some things. Pianos for example. You will hear a spruce soundboard piano going out of tune within days as humidity swings take effect.

Don't worry too much. What is best avoided is big swings and sudden changes.