Wood ambient moisture intake time.

[rafezetter]

Hi all

There's been threads about drying wood and such but my question is one of what happens after it's been stored and dried but you want to work on it.

I've had wood stored in my bedroom for quite some time now, more than a year, and my el-cheapo meter says between 5-9% (I'll err on the side of 9%) but I do all my woodworking outside, and once started it might have to stay out there a day or two.

The issue is mainly jointing up planks for boards and how the wood might behave, the wood is old T&G pine (no idea which) planks that had been used to board up a room in the 70's (like they did) 13mm thick.

How much time will I have to work it before it might become an issue?

I also have some very old, what might have been roof sheathing, boards 12" wide by 1" thick (can't tell the wood as they are so grimy) that I want to use for a dining table top.

Will I be restricted to mostly warmer weather outdoor work, or if I work it then move back indoors in the evening, will I be ok?

thanks in advance

Austin

 

[deema]

I think that it is a question of the type of projects you are doing. If it's highly accurate cabinet making, with accurately cut dovetails, fine stringing etc etc, I would not ever leave anything outside. If it's hard wood, again it would not leave it outside. If it's softwood, which tends to be more stable dimensionally once dried out, a few days as long as it does not get wet should be OK for most forms of joinery.

If you have flattened and squared stuff ready for further work, I would always clamp the pieces together to help keep them straight and true if I'm leaving them overnight. I try to clamp flat sawn timber with the rings centres together. This I believe helps to stop the face that will cup (concave) drying out faster than the other side.

If it's sunny, I would always ensure the timber is shaded and air can circulate all around. I once left some jambs for a door frame on my bench in summer and the early morning sun did a fine job of twisting them on a few hours into a banana by the time I had got back to them at about noon!

 

[Random Orbital Bob]

Yup......its a crap shoot to be honest. I would only work on them outside when actually processing them (I'm guessing you're doing this to avoid the mess inside??) and then once cut, planed, sanded etc rehouse them in an environment close to their current ambient conditions.

When I process sawn timber and finish it PAR, if it's to be left overnight I also clamp it to solid flat workbench to kep it square and flat. Its not just the moisture content changing that puts it at risk but also the changes to the inner tensions set up by the grain when you cut or plane it. However, if the project is something rough, don't worry so much.

 

[rafezetter]

Hi Deema, thanks for that info, that gives me some guidelines to work from, and I didn't realise (bugger off american spellchecker!!) hardwood suffered more than softwood, could anyone explain why that is?

The projects would be a dining table for the 12" stuff, but I had a possibly canny (or maybe crazy stupid) idea for keeping that flat by having a plywood backer to the top so the boards are glued to that although the final piece would be in a centrally heated house.

The T&G boards I was thinking of making some play chests / ottomans with them.

I found out about the direct sun effect last year - and used it to uncup some old feather edge planks for my planter (in my projects below).

 

[rafezetter]

Yup......its a rubbish shoot to be honest. I would only work on them outside when actually processing them (I'm guessing you're doing this to avoid the mess inside??) and then once cut, planed, sanded etc rehouse them in an environment close to their current ambient conditions.

When I process sawn timber and finish it PAR, if it's to be left overnight I also clamp it to solid flat workbench to kep it square and flat. Its not just the moisture content changing that puts it at risk but also the changes to the inner tensions set up by the grain when you cut or plane it. However, if the project is something rough, don't worry so much.

Well I live in a rented house so no chance of doing anything indoors pretty much - no space - unless I sell my big sofa n stuff and use that area for hand planing, an idea that's crossed my mind more than once, but sizing / sanding etc would still have to be outside.

I'd read about released tensions before and will prolly size with a bit extra, leave a day or two then finalise; but I'm hoping as most of this is old previously processed wood that it's done all it's going to do apart from anything moisture related.

 

[blackrodd]

Yup......its a rubbish shoot to be honest. I would only work on them outside when actually processing them (I'm guessing you're doing this to avoid the mess inside??) and then once cut, planed, sanded etc rehouse them in an environment close to their current ambient conditions.

When I process sawn timber and finish it PAR, if it's to be left overnight I also clamp it to solid flat workbench to kep it square and flat. Its not just the moisture content changing that puts it at risk but also the changes to the inner tensions set up by the grain when you cut or plane it. However, if the project is something rough, don't worry so much.

+1 For the above, Wise words indeed! Rodders

 

[Sgian Dubh]

Hi Deema, thanks for that info, that gives me some guidelines to work from, and I didn't realise (pipper off american spellchecker!!) hardwood suffered more than softwood, could anyone explain why that is?

Yes. I strongly suspect that assertion is incorrect. How quickly wood adsorbs or desorbs moisture has more to do with its structure and its chemical makeup than it has to do with whether it's a softwood (coniferous) or a hardwood (deciduous). Some softwoods produce hard wood that is dense (yew for example), and some hardwoods produce soft wood such as balsa which is light and has many voids. Adsorption and desorption of moisture tends to be slower in dense woods than in soft woods. You also have to take into account a hysteresis loop that's driven by moisture cycling, basically saying the ability of wood to adsorb and desorb moisture reduces over time and over a number of cycles.

However, in answer to your original question, it's likely that bare wood about 1" thick at, say, 8% MC left fully exposed in RH conditions of about 70-80% RH or more (typical for an uninsulated and intermittently warmed shed in winter) for about two weeks will rise to something in the region of 13% MC. I came to this conclusion after conducting experiments with some unfinished wood samples to determine how much wood changed dimensionally as its MC changed. Slainte.