Thursday, 29 April 2021

How much moisture does wood lose when it dries out?

We once had a client who ran a facility for drying wood (to make wood chips for incinerators). I asked him how much lighter wood was after you'd let it dry out for a year, i.e. how much moisture it lost and he didn't appear to know.

So when I chopped down some leylandii branches a year ago, I weighed one chunk, marked the weight and date on it with felt-tip and tucked it at the bottom of the pile so I wouldn't burn it by mistake.

The results are in - original weight 2,107 grams; weight today 1,080 grams. In other words, it was nearly half moisture (it's still surprisingly heavy). I live and learn. I'll weigh it again in a year if it's still there.


Doonhamer said...

It would be interesting to know if / how much the volume / density changes.
Which is best for boats and rafts.

Mark Wadsworth said...

D, don't use leylandii, it's bloody heavy. I filled the sink and dropped a piece in, it's still two-thirds submerged (after a year of drying out). A nice bit of pine which had been drying out for a century was slightly less than half submerged.

James Higham said...

Makes wood an interesting building material.

Andrew Carey said...

That's a great little experiment. Please keep it going.
Provisionally it supports a claim that trees are vertical columns of water, and so they benefit the climate change by reducing sea level rise and flooding, compared to the counterfactual of pasture. CO2 uptake is rather an irrelevance so long as the land supports vegetation.

Bayard said...

D, some woods become less dense as they dry out, e.g. chestnut, but others remain at the same density, but shrink, e.g. oak.The first type is obviously better for making things out of, although durability is also a factor.
JH, I read an interesting article years ago, called "The Wood That Missed Its Vocation", about how Cupressus Leylandii was as fast growing as spruce, the main construction timber, but much stronger and more durable.

Bayard said...

Mark, I found a list on the internet, giving the percentage of water in various green (freshly cut) timbers. I'm not sure if it gave the figures for Cupressus Leylandii, but poplar and elm were the wettest at 60 and 59% water and ash and sycamore were the driest at 32 and 41%.

Sackerson said...


Mark Wadsworth said...

B, if leylandii were so great for timber, they would use it. I suspect the reason are
1. It's a bush not a tree, so you don't get big trunks to slice up into floorboards and joists.
2. Even when dry, it is bloody heavy (it might be stronger, but hey).
3. It is much more flammable than other wood.

Re water content, thanks, so leylandii at approx. 50% seems plausible.

Bayard said...

" It's a bush not a tree, "

From Wikipedia, "A large, evergreen tree, Cupressus × leylandii reaches a size between 20 and 25 m high". Some bush!

Mark Wadsworth said...

B, the ones I've seen were all bushy. But I live and learn.

Why do you think they don't use it?

Bayard said...

Pure conservatism, probably. No-one wants to plant Leylandii and grow them only to find no-one wants to buy them as they aren't familiar with what they are. Everyone knows about spruce, so that's what they will stick to.