Thread: Why is ancient (recycled) hardwood so much harder?

Cell colapse.

Once the timber dries out , and moisture is removed then the curing process begins,

100 year old timber has gone through thousands of cycles of hot,cold wet and drying out,

like any material this affects the cellular structures, .

..They just made em tougher back then....

calls it "case hardened". Recently we turned some fresh tallow wood. Wonderful. Could even get curlies. Usually old telephone poles. No curlies there!

Here is a bit about it! But it doesn't talk about the "hardness" of the timber to work.

Case Hardening in Timber


I guess it is just super dry! Like an old fence paling that you can't hammer a nail into!

Thanks everyone for your answers...

Originally Posted by rustynail

Cell collapse.

Originally Posted by vk4

[...] affects the cellular structures, .

Thanks guys. That gives me the clue. I guess what you're saying is related to this:

Cytorrhysis - Wikipedia, the free encyclopedia

i.e., collapse of the vacuoles in the cells.

Vacuole - Wikipedia, the free encyclopedia

Originally Posted by tea lady

... case hardening ...

This seems to be something different than cell collapse but perhaps I misunderstand. Is case hardening simply cell collapse on the outer layers of the timber only?

Very old timber seems to be super-hard all the way through and doesn't exhibit much movement even if I thickness off a generous chunk of surface layer.

Cell collapse is part of the answer but another contributor to wood hardening is the natural resins and other chemicals in the timber react with air to form harder materials than living wood. Because the outside surfaces are exposed to a lot of air they harden first and fast so that causes case hardening. As the wood dries out and air slowly makes its way further into the wood through cracks etc it eventually becomes harder all the way through.

I have some ancient black red-gum, and some very old red-gum fence posts that were at a church for >100 years, and both are similar hardness for me when turning.

Originally Posted by BobL

Cell collapse is part of the answer but another contributor to wood hardening is the natural resins and other chemicals in the timber react with air to form harder materials than living wood.[...]

Ah. Thanks.

I guess that would also partly explain why even stainless steel screws tend to snap if you try to withdraw them from an old deck. (?)

Originally Posted by dai sensei

I have some ancient black red-gum, and some very old red-gum fence posts that were at a church for >100 years, [...]

Red-gum posts in-ground for >100 years?? I would have expected the bottoms to have rotted significantly before that.

Every day presents an opportunity to learn something new.

Great signature line! Sometimes I get the feeling that most other people in the world regard each new day as an opportunity to do only variations on the same thing over again.

Cell collapse does not have to be total cell failure. The shedding of moisture and resins causes the cell to contract in size. This process is ongoing for as long as the timber lasts. Far quicker during initial drying (seasoning) and then slowing over the life of the timber with fluctuations caused by atmospheric conditions. Case hardening is this process being excellerated due to early stage rapid drying of outer surfaces causing premature shrinkage of outer cells. This in turn can cause inner cells to become sealed so moisture can no longer escape, thus inhibiting seasoning. In severe cases the timber can show definite signs of dimensional change in sectional shape caused by cell collapse caused by too rapid drying.

I would rather turn old timber than green timber. At least you know what you have as finished product is not going to crack and warp. ( at least I hope so )

Originally Posted by cookie48

I would rather turn old timber than green timber. At least you know what you have as finished product is not going to crack and warp. ( at least I hope so )

Yeah, that's why I like to use recycled timber for exterior use when the thickness must exceed 45mm. OTOH, I found out the hard way that epoxy filler (Builder's Bog) is not long-term durable for filling the large holes.

Old Fart (my step daughters named me)

Huh? Farts are rarely more than 24 hrs in the making, so yours are no older than theirs.

Wood in standing trees is wet. The cells are full of water for a moisture content of 35% more-or-less. The only moving water is in the most recent 10-15 yrs of growth.
At the molecular level, much of the water is "bound water". These H2O are stuck to all kinds of cellular structures as a coating, effectively preventing them from touching each other.

Dead tree, water loss begins. Outdoors, under cover, the MC will eventually settle down to something like 12-15%. The longer this situation exists, such as timber in service, the deeper the drying process reaches.

At the molecular level, much of the bonded coatings of water are evaporating. This allows the cellulosic and non-cellulosic components to touch each other. Without the water coatings, they stick and they will not come apart, hence the apparent increase in toughness.

Originally Posted by Robson Valley

At the molecular level, [...]

Thanks for the extra detail.