wood moisture

[Ring]

Hi all looking for advice on wood moisture ,what should i be looking for in oak,i have made a few things lately but my last project [bedside cabinets]looked great when i finished it but they have started to warp badly,i have not got heating in my garage yet and i biscuit joined and glued all my pieces together but they are starting to warp really badly any advice would be great tnx
Jim

 

[Mdotflorida]

Hi Jim

Sorry about the project.

Did you acclimatise the wood indoors before the build ?

I spent the weekend rough dimensioning a load of Oak for a bedroom project. It is now stickered in the in spare room where it will stay for a couple of months before I get around to using it.

Jeff

 

[woodbloke]

Jim - sounds like your oak was to 'wet' (MC too high, at or over 20%) for indoor use, as Jeff has said it should have been aclimatized indoors for a few months before use - Rob

 

[Big John]

One cause may be the orientation of the growth rings on the boards. The general rule is to alternate to minimise warping.

 

[Alf]

One cause may be the orientation of the growth rings on the boards. The general rule is to alternate to minimise warping.

All that happens is you get a rippled effect as one board cups one way, the next the other way and so on. Many, many respected woodworkers totally ignore it and pick orientation on the basis of figure. Better to acclimatise the wood to the conditions it's likely to experience.

Cheers, Alf

 

[patl]

While we're on the subject, is there a rule of thumb about when you should sticker and when its not necessary? I've just received a load of planed boards which are between 10 and 15%, do they need stickering or not?

Thanks,
Pat.

 

[Mdotflorida]

While we're on the subject, is there a rule of thumb about when you should sticker and when its not necessary? I've just received a load of planed boards which are between 10 and 15%, do they need stickering or not?

Thanks,
Pat.

Hi Pat

I always sticker when storing wood. It lets the air circulate.

Jeff

 

[woodbloke]

Agreed - Rob

 

[Sgian Dubh]

Jeff, always?

Let's say you purchased timber that is currently 8%MC and your workshop has an average RH at this time of year of 75%, and the wood you've purchased is for a living room piece. Would you sticker the wood in your workshop, or close stack it?

What rate of moisture regain or loss would you expect if you put this 8% wood in your workshop, either close stacked or stickered?

If you think about it, does it make sense to offer the blanket advice that all wood should be stored in stick before you turn it into furniture? Slainte.

While we're on the subject, is there a rule of thumb about when you should sticker and when its not necessary? I've just received a load of planed boards which are between 10 and 15%, do they need stickering or not?

Thanks,
Pat.

Pat, the information that's needed before a recommendation can be given is what the wood is to be used for. Outside furniture exhibits different MC values to indoor furniture. Consistent 80% RH equates to ~16% wood MC and steady 40% RH results in wood eventually settling at about 7% MC. In truth RH values are much more dynamic than this and change by the minute, the hour, the day, weekly and seasonally.

If your workshop is unheated and poorly insulated then RH is likely to be around 75% to 80% in winter, and in the summer it will reduce to approximately 65% to 70%+ If it's insulated and heated to the same level as your house then RH will hover between an average of about 40% in winter to about 60% in the summer. With some insulation and intermittent heating you'll have RH figures somewhere between the two examples given.

Therefore stickering the wood in your workshop may not be of any real benefit. If you come back with some more specifics I'm sure some useful advice could be offered. Slainte.

 

[Mdotflorida]

If you think about it, does it make sense to offer the blanket advice that all wood should be stored in stick before you turn it into furniture? Slainte.

I don't think I did offer blanket advice. I simply stated "I" always sticker.

Therefore stickering the wood in your workshop may not be of any real benefit.

It may not offer a benifit but is there any harm. ?

Jeff

 

[patl]

Ooh more information than I can shake a stick at :wink: Where does all this come from? Just general knowledge or is there something I should be reading?

Well, the wood is oak and ash, ultimately destined for inside use. Its being stored on racks in the garage which is integral to the house and whilst having a few cracks around the garage door also contains the central heating boiler and tank so is probably not more than 10C, 15-20% RH away from indoor conditions (based on current thermometer readings).

Thanks,
Pat.

 

[promhandicam]

this is a useful link which gives information on moisture content in wood. Steve
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[Sgian Dubh]

I don't think I did offer blanket advice. I simply stated "I" always sticker.

True Jeff, you didn't offer your practice as blanket advice, but it could be implied from your original one line response that stickering per se is a 'good thing.'

You didn't give a reason why you always sticker. What's the benefit and what are the disadvantages of stickering up wood? It's not always a good idea to sticker timber-- see below.

Therefore stickering the wood in your workshop may not be of any real benefit.

It may not offer a benifit but is there any harm. ? Jeff

There could be. Let's take a realistic scenario. Some timber is acquired that currently measures out at 8% MC. This is about the right MC for wood that is to go into a residential property in the UK, assuming good insulation and heating. A typical UK house will exhibit RH (relative humidity) values of about 40% in winter and about 60% in the summer. Household furniture in these conditions will swing between about 7% MC in winter and about 11% MC in the summer.

Wood at 8% MC as described above is at about the lower end of the range you'd expect it to experience in service. Edge joints (e.g., table tops) for one survive better as the wood expands (compression) compared to when they shrink (a tensile force.) So before making the piece of furniture you'd want to keep the wood as close to 8% MC as possible.

Now, if you take your 8% MC wood out to an unheated workshop in the UK with poor insulation, typically the RH will hover between about 65% and 85% as I described before. If the wood is stickered this facilitates moisture exchange so the wood will gain moisture, and this 65% to 85% RH range means the wood will settle out at somewhere between 13% and 18%, probaly at about 15% or 16% MC. These numbers are higher than internal furniture will experience, so stickering would be detrimental.

You'd be better to close stack the wood in the relatively damp workshop (if it's the case that you must store the wood there rather than in the house. Close stacking means that the boards at the centre of the pile will gain approximately 0.2% of moisture per four weeks. In theory then you could close stack wood that is 8% MC for about five months before it would rise to 9% MC. Of course the outside of the pile would be exposed to the higher RH conditions. Wrapping the wood tightly with plastic sheeting will reduce the speed of moisture gain here substantially.

What I've just written is no more than a summary of one possible scenario, and it fails to take into account a whole load of variations in circumstances, conditions and any exceptions that could have been discussed, but it does illustrate a situation where stickering a pile of wood would not perhaps be the best choice, and could even be extremely detrimental to the success of a project. Slainte.

 

[Sgian Dubh]

Ooh more information than I can shake a stick at --- is there something I should be reading?

wood---- being stored on racks in garage ---- central heating boiler and tank so is probably not more than 10C, 15-20% RH away from indoor conditions (based on current thermometer readings). Pat.

I guess until I finish my definitive tome on timber technology (ha, ha), if I ever write it, an excellent source of knowledge on the subject would be R Bruce Hoadley's Understanding Wood, about £23± from booksellers like Amazon. I suppose I get my knowledge of the subject from more years than I care to remember studying it in detail.

As to your specific question I'd guess that stickering your wood that is currently about 15% MC in your garage would bring the MC down. At this time of year Absolute Humidity (AH) values are low anyway-- cold air can't carry much water, and heating the air reduces RH substantially. (AH is a measure of the actual amount of water vapour carried in the air. RH is related to this.)

Temperature is not a guide to RH conditions though. It can be very hot, e.g. 38ºC and very humid, e.g., 90% RH. RH is the critical number to watch for, although temperature does have a minor influence on the final MC of wood, as does altitude and barometric pressure, three influences on wood MC I don't really have time to go into in a quick forum response.

Your best bet if you can afford it (about £15) is to get a digital hygrometer from somewhere like Maplins. This will give you a rough idea of the RH conditions in your garage on a week by week and month by month basis. If you know the average RH (generated by taking daily readings, noting them, and doing some sums) you'll be able to work out what sort of MC range your wood is likely to experience over the year.

Buy two hygrometers and you could monitor your workshop (garage) and the inside of your house too. This would give very detailed information that would allow you to avoid surprises. Of course, you'd also need a moisture meter to measure the average MC of your wood from time to time. Slainte.

 

[CHJ]

....snip... but my last project [bedside cabinets]looked great when i finished it but they have started to warp badly,....snip...Jim

Looking at another aspect that may have influenced the stability other than just moisture content.

Did you thickness the pieces at all, and if so did you take equal amounts of both faces?

 

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[patl]

I probably shouldn't admit this, but actually I do have thermometer/hygrometers in the garage, the conservatory and on all floors and they're all logged to my computer every 10 minutes...
So finally I have a reason better than 'just curiosity' to know what the RH is throughout the house )
(am I sad or what? My excuse is that the weather station was too good a deal to miss and I needed an additional thermometer to go with the 'proper' weather station, and this package happened to come with 3 remote thermometer/hygrometers. You can never have too much technology in my book :roll: )

 

[Ring]

Hi all and thanks for all the replies. i purchased 2 pallets of oak from my local saw mill £100 my mate is the boss so got a good deal on it ;-) it is stored outside raised up on pallets and covered with 3 layers of polythene and a great big plastic tarpoline, it varies in sizes from 2"x1" 3"x2" random lenghts probably about 8 or 9 cube of the stuff,i cut it to approx lengths and stored it in my garage 25ftx16ft double glazed windows and tiled roof ,then i dressed it out on my planer thicknesser and started my assembly . i made sure i was taking the same of each side and when gluing up made sure to alternate the grain i have been swithering about a woodburning stove for a while so i think my first step will be to order one at the end of this month and make a racking system up inside the garage to stack the wood and hopefully get the moisture to a better level.
Jim

 

[Sgian Dubh]

Pat, as you have a weather station monitoring all over the place I assume you understand 'weather' pretty well. I suspect I'd be teaching you to suck eggs if I tried to explain to you all there is to know about the relationship between the following: AH, RH, barometric pressure, altitude and air temperature-- the chances are you know more about this topic than I do.

It sounds like you just need to get to grips with how these factors affect moisture content in wood, develop an understanding of moisture gradients in wood, and an understanding of tangential and radial shrinkage, etc. in response to changing wood MC. Hoadley's book should put you on the right track. Slainte.