moisture content of wood

[ciscoeuk]

hi all

i been given a large chunk of unseasoned cherry for services rendered,

i would like info, posts or charts for moisture content of wood, before i can use

also looking for moisture gauge??

 

[Doug B]

Rule of thumb for drying is 1 year per inch of thickness, when air dried.
I have not long been given a 15' x13"x 9" green oak beam which i`ve had cut up into 2" planks to help speed up seasoning.
The trick is is to have some idea what you are going to use it for, then cut it up oversized to your requirements.

 

[9fingers]

I bought a cheapo meter from ebay
4 pin model MD-4G.
At the time several vendors were selling the same model but badged with other names. I bought from Hong Kong at a lower price.

I've nothing to compare it against but damp wood brought into my shop gradually achieved the same reading as stuff that had been there for a while.

The was about 10-11% on the display. I only wanted a comparator and it certainly does that and lots cheaper than other meters for sale in UK.

As for the cherry, you need to cut it into the rough sizes you want and then air dry it steadily - many people say 1 year per inch of thickness. I'm not a turner but I think people do turn wood in the green state. Ask in the turning section.

hth

Bob

 

[bjm]

If you want to determine moisture content you will need a balance and an oven. Take a piece of wood* and weight it (Wet wt). Dry in an oven at just over 100 deg C (105C recommended) for an hour or more depending on size (you can use a microwave oven but you may regret it when you have to clean it out as the wood can explode) - weigh again and put back in oven for ten minutes - reweigh until you get a stable reading (Dry wt)

* The size required will depend on the accuracy of the balance you have - for digital kitchen scales you may need something the size of a small matchbox.

Moisture content is: ((Wet wt)-(Dry wt)/(Dry wt)) x 100

(as this calculation is based on the dry weight of the wood you can get a result that is in excess of 100% if the timber is freshly cut (green)).

Moisture meters are only reliable in the range 5-30% mc so wouldn't be much use in the early stages before drying.


Brian

 

[Ironballs]

Cherry moves like hell until it is seasoned so make sure it is nice and dry before using

 

[ciscoeuk]

Rule of thumb for drying is 1 year per inch of thickness, when air dried.
I have not long been given a 15' x13"x 9" green oak beam which i`ve had cut up into 2" planks to help speed up seasoning.
The trick is is to have some idea what you are going to use it for, then cut it up oversized to your requirements.

looking to make a few hand tools with possbly a jewerly box i there enough left, but it depends how i cut it

will be slabbing it in to 1 - 2 inch chunks

 

[CHJ]

...i been given a large chunk of unseasoned cherry for services rendered,
....

Then the first thing you need to do is seal the endgrain and prevent it loosing any significant moisture until you have decided what you intend doing with it.

If it is in log form then there is a need to urgently decide what you want to do with it and at least cut it through the central pith.

Cherry in my experience is very prone to splitting as it dries, try and equalise the rate of moisture loss over the whole of the surface and slow down the drying as much as possible.

The thicker the sample the more risk of it splitting.

 

[ciscoeuk]

brian

thanks for that

-------------------------------

i will take onboard whats been offered

when is it best to use at 15 - 20% moisture??? or less

 

[bjm]

Moisture meters are OK below ~30% mc but if you're looking to make furniture or anything that will be indoors you are aiming for around 9-10% mc.

30% mc is the approximate moisture content at which shrinkage will begin to occur as further drying takes place. It is called fibre saturation point (fsp) and is the point where all the free water has been removed from the cells and the only water remaining is bound within the cell wall. The free water has no impact on the dimension of the cells but the bound water is physically bound to the cell wall and 'bulks' it (a similar analogy is the effect that 'bulking agents' in washing powder have on cotton towels). It's removal will therefore have a direct bearing on the physical dimensions of the cells, and hence the overall dimension of the wood.

Brian

 

[ciscoeuk]

thanks bjm

i intend to use some of it to make tools, handles and possibly draw fronts depends on e=what i can get out of half of a 5ft log

i have decided to slab at 1,1/4 in to allow for shrinkage and plaining!

should this be ok ?

 

[chipchaser]

Hi Ciscoeuk,

Good advice on here so far. If you can reduce the log to pieces sized to suit the end use with allowance for shrinking and planing away twist rather than leave it as thick planks it will dry out quicker. If not plank it and seal the ends. Stack with sticks between to allow air flow and store under cover in a dry well ventilated place out of direct sun. Keep the lowest plank 6” or more above ground level.

You are unlikely to get the timber dry enough for internal use just by air drying outside. You will need to bring it into a comparable environment to reach the desired moisture content. Practically you will probably need a moisture meter to know when the timber is ready unless you can leave it drying naturally for a long time and can spend time sampling and weighing pieces of the wood. If using a moisture meter take several readings along the piece as it may vary.

If a wood turner making bowls turn roughly oversize and thickness whilst green and then dry before final turning. Search this site for more advice on this.

Key moisture levels in timber are: less than 20% to resist fungal decay and 18% is safer; 12% or less for joinery to avoid significant movement in heated buildings but much lower if you have a hot dry environment, 8% or maybe even 6 %.

There is some useful info at these two locations:

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr06.pdf

http://www.comproteccanada.com/meter.htm

The first document is 20 years old but the basic science hasn’t changed.

You need to follow all the links on the Comprotec site to see all the info there. I have never used one of these meters but they are not expensive for what appears to be a robust professional tool. Protimeter was the uk market leader with architects and surveyors but they are now owned by GE and are relatively expensive. The cheaper Protimeter models are aimed at assessing damp in buildings rather than accurate measurement of timber moisture content.

If you google DIY kiln drying timber you will find lots of info, mainly from USA, on building your own kiln which could be solar powered or artificially heated. It could be as simple as a piece of large plastic pipe or duct with a light bulb in it.

Also try googling Drying timber in a microwave. I had some success with this. Put the timber in a plastic bag in the microwave, maybe when the wife is out :wink: I found it didn’t make a mess or smell but I wouldn’t try this with say Yew because it is toxic. Of course the size is limited to what will fit in the microwave.

Regards

Graham

 

[ciscoeuk]

graham thanks for the info, great help in my decision on dimentions to cut and dry

decison made

i going to cut 1"-1/4" thick to allow for shinkage and plaining, then stack in the eves for my apex roof in the garage, with a 25kg weight on top to keep flat the final boards i have worked out will be 9 x 12"x 3/4" finish size

i think this will do the job

i have slso found out today that i will be getting a share of a 22' x 4' dia ash tree for free, for fixing this chap computer!!, can't be bad

by the way if any of you need computer help drop me a pm with email and phone details,

 

[joesoap]

There is a very good article in the Dec/ Jan edition of the Brlitish Woodwoorker mag on that very subject of turning with 'green' . Seems to be common practice with the turning fraternity . Cheers !