air dried v kiln dried

[se7enthdevil]

i've just be cutting up the last of my sycamore slabs for my skittles that i bought 4 years ago. they had already been sitting around for another 4 years so are at least 8 years dry.

 

as a user of both i have noticed that the quality of the air dried is better than the quality of any kiln dried timber i've ever used. species i include in this comparison are oak, beech, elm and sycamore.

 

i should point out that i am referring more to the eventual hardness of the timber over colour or grain quality.

 

whenever i use sycamore or beech for my skittles the kiln dried material is always nice and clean as you would expect from a lumber yard but a bit softer than the air dried timber i get cut for me by other arbtalkers.

 

my question is,

 

is there something that kilning does to the wood or have i just been lucky with my air dried timber i've bought over the last few years?

[spiral]

I wood guess heating up anything with a substantial amount of water in it will soften it slightly?

 

Its the basis of cooking really.. {mind you over cooked is the opposite.}

 

But thats just my thoughts. I have no evidence.

 

I am sure theres some out there though!

 

To me kiln dried seems less tough than many air dried timbers as well.

[se7enthdevil]

annoyingly the toughness is what i would like as it's for the skittles which get quite a beating most nights...

 

i had thought that it was possibly the heat that broke down some of the lignin between the cells???

[spiral]

Indeed!

 

If I think about it a little more, it a 1 inch hazel, yew or ash walking stick air dried is very resilient, Out of a kiln it would snap like a matchstick under pressure....

 

Many ash tool handles on spades forks etc. seem the same as well.

 

Found this..

 

This research seems quite empirical...

 

http://naca.central.cranfield.ac.uk/reports/1920/naca-report-68.pdf

 

The Conclusion seems to be many timbers vary, but with many timbers kiln dried, toughness & resistance to shock will be damaged.

 

That seems to match both your & my experiences..

 

Guess that means that's the reality...

[se7enthdevil]

some good info there...

 

 

i've long suspected that most companies fast track their kilns drying it out way too fast rather than drying it out properly.

[slackbladder]

Very interesting thread

[slackbladder]

Iv'e always preferred air dried mainly because I can't see the point of kiln drying to something like 8% and then putting it in the shed for it to take on moisture again, Plus air dried works better

[spiral]

some good info there...

 

 

i've long suspected that most companies fast track their kilns drying it out way too fast rather than drying it out properly.

 

My father who was a timber buyer for a London importers {& later A sales manager.} from about 1950 onwards, was saying the same thing in the 70s...

 

 

Ideally the timber is nearly constantly monitored & everything adjusted accordingly..

 

Don't reckon that ever happens today unless it for their own flooring in their own house..

 

That's Assuming they have the best data for each timber in the first place..:

[agg221]

Iv'e always preferred air dried mainly because I can't see the point of kiln drying to something like 8% and then putting it in the shed for it to take on moisture again

 

There can be, depending on the species. You can think of the structure of wood as being like a bundle of drinking straws, with membranes blocking each straw at periodic intervals along the length. There are little holes connecting the straws and through each membrane, allowing water to flow (this is how sap is transported). This is the same route by which water flows out during seasoning and back in when left in the shed.

 

The little holes are covered with flap valves. This is why trees don't keep on bleeding, despite the enormous pressure from the head of sap at the top to the bottom. These flap valves can normally open and close. In some species, once you get below a certain moisture content, the flap valves close permanently and cannot re-open even if the moisture content is increased. This makes water transport much harder, so the timber is far less prone to swelling and contracting. Spruce is a particularly good example.

 

Alec

[TimberCutterDartmoor]

Lignin gets lost when kilned... I think.