# Air Dried v Kiln Dried



## BradNaylor (31 May 2009)

This thorny topic has cropped up again on a thread of Karl's over in the Projects forum.

There seem to be two camps.

I use KD timber simply because that is what is stocked by all the suppliers I know. People such as John Boddys, British Hardwoods, and Irmass all sell huge quantities of KD hardwoods to furniture and flooring manufacturers, seemingly without any problem. 

My only experience of air-dried timber is a couple of small local forestry operations who plank their own wood and leave it to dry in sheds for several years. They sell almost exclusively to the building industry who use the timber in external situations or possibly for oak beams in barn conversions etc. I have tried some air dried oak for furniture and found it awful!

The other camp contends that KD timber is rubbish and that air dried is the only stuff to use.

I am far from being an expert on this matter and would love to learn more.

Cheers
Brad


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## woodbloke (31 May 2009)

Brad - you only need to looks at the recommendations of people like Alan Peters, David Savage and the Barnsley 'shop to realize that the _only_ stuff they use is air dried. Savage in a recent issue of BW described kilned timber as having "all the life sucked out of it" which is a fair description. I've used kilned timber in the past thats been full of splits and it's 'carroty' when it's being worked...bloody awful :evil: to say the least - Rob


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## wizer (31 May 2009)

The only air dried timber I have used is this Oak from Mike. I assume it English Oak and air dried. All I can say is that it is surprisingly nice to turn and carve. Ok, so not like carving Lime, but no where near as brittle as the KD stuff. 

Just my limited experience.


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## MikeG. (31 May 2009)

I pretty much exclusively use air dried, but only because we are short of suppliers around here and it is pretty much all that is available. I can't comment on the alternative, therefore......but thought I would mention that if you are planning to steam wood, air dried is almost obligatory.

Tom, yes, that oak was air dried.

Mike


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## woodbloke (31 May 2009)

wizer":n482m29o said:


> The only air dried timber I have used is this Oak from Mike. I assume it English Oak and air dried. All I can say is that it is surprisingly nice to turn and carve. Ok, so not like carving Lime, but no where near as brittle as the KD stuff.
> 
> Just my limited experience.


I think one of the issues is the amount of hand work done with the timber. If it's used exclusively with machines with very little hand work, then you don't really notice the difference. It's only when the stuff gets on the bench and you hand plane it or do a lot of work on it with hand tools does the user notice the glaring difference. If you've never used good air dried stuff you also won't be able to tell the difference 'cos the KD timber becomes your reference, good air dried stuff is almost akin to working with a very hard cheese (almost)...it's that sort of consistency - Rob


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## crazylilting (31 May 2009)

Each wood has it's place. Those who use hand tools and those who use it for commercial applications. I've used both, and to be honest i don't think many people air dry their wood well enough to use. It's frustrating getting wood from some bloke who boasts that it is the best only to find out it is absolute rubbish for the job it was intended for.

One way around this is to have a small kiln to finish the wood off. It doesn't have to be high tech just enough so the wood is usable. I for one can not afford an inventory of wood to use several years down the line. I know a fellow woodworker that fells his own wood and stores it and yes also has his own kiln made out of a shipping container. 

He has so much wood he could sell it and retire i reckon. He doesn't mess around. If the wood is air dried properly it is wonderful to work with, but chances are the wood doesn't look that great either. It's rare to find air dried wood that is of high quality in the parts where i live. 

If i had the land and the money i'd do what my joiner friend does but i don't so i go to the wood wholesaler and buy kiln dried wood that is stable enough to actually do the jobs i have on hand.


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## Doctor (31 May 2009)

What does "carroty" mean, is it similar to "turnipy"?


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## motownmartin (31 May 2009)

I bought a load of air dried Oak and was going to make a large storage chest, I started to cut the legs and rails and one or two splits started to appear, no worries, I thought I could position these so they would be hidden, I proceded to plane and thickness the stock only for a lot more splits to appear, so many that I stopped the job altogether.

So I lost confidence in air dried timber.

It may have been a bad batch or somebody telling me porkies, the stuff is still moving now, I put most of the wood I use in my sun lounge for a month to give it a good drying, it's like a kiln


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## marcus (31 May 2009)

I wonder if there is a difference between timber that has been kilned by heat and that which has been kilned by dehumidification? I used to swear by air dried because of the ease of working, but recently I bought a big load of oak from David at Interesting Timbers that had been kilned in his dehumidifier. It was probably the best oak I have ever used (I work mostly with hand tools and hand planed everything). It planed beautifully, and didn't feel like the commerdcial kiln dried stuff at all. To be honest I couldn't have told the difference between it and air dried.

Perhaps the baking that timber receives in a traditional kiln affects the wood in a way that dehumidifaction doesn't? 

Does anyone else have any experience/opinions about this? 

Cheers

Marcus


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## Paul Chapman (31 May 2009)

I've had problems with kiln dried timber as well - lots of splits and cracks and case hardening. Also many stockists sell kiln dried stuff which has been stored in damp conditions after kiln drying.

Air dried for me every time now.

Cheers :wink: 

Paul


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## marcus (31 May 2009)

Another thought - could it be that most timber which gets kiln dried is not that good before it even goes in the kiln? The oak which you find on the racks at your typical big commercial timber merchant is not the same quality as the oak that will be selected to be air dried for furniture making. I've used poor quality air dried timber that was just as irritating to work as a lot of kiln dried stuff you come across....


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## woodbloke (31 May 2009)

I think it may also depend on just _how_ it's been kilned...often too quickly IMO which is what causes the defects to appear, 'specially in oak - Rob


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## CWatters (31 May 2009)

If it's anything like buying firewood then "air dried or "seasoned" can cover a multitude of sins. One place "seasoned for a year" means they cut it into 10" logs and then store in a well ventilated barn. In another they mean the tree fell down in last winters storms and has been laying on the ground where it fell ever since, they've just been hired to clear out the tree falls and will cut it to whatever size you want. 

I'm still really a novice at wood working. How is "air dried" defined and controlled? Do many places properly air dry timber these days or is it just a euphamisim for "not kiln dried"?


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## woodbloke (31 May 2009)

CWatters":2sm57jk9 said:


> How is "air dried" defined and controlled? Do many places properly air dry timber these days or is it just a euphamisim for "not kiln dried"?


 
It should be 1 year per 25mm of thickness...ideally :wink: Timber should be dried under cover out of direct sunlight and the rain with good air flow around the boards. These are ideal conditions which are can _sometimes_ be found in larger commercial woodyards. At Yandles, some of their stuff is conditioned under cover but a lot more is out in the open, so you really need to trawl through the stuff to find anything that's half decent. Some of the smaller yards though may only offer timber that's been air dried as they may not have access to a kiln - Rob


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## yetloh (31 May 2009)

It is OK for professionals like Barnsley and Alan Peters who have the space and resources to buy in logs and either convert them or pay for someone to do it to their specification, but the average amateur or small maker has to buy what they can readily get, which is KD. I work extensively with hand tools and have occasionally worked with AD and, yes, it is nice to work with. But the reality is I have no ready source of good quality AD. So I buy KD from reputable hardwood suppliers - usually W L West near Petworth or English Woodlands at Cocking. 

I have never had any problem with their timber. It may not be quite as nice to work but I think it is easy to exaggerate the difference. In the end, quality is what matters which is why I would never buy from a general timber merchant. 

Jim


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## Doctor (31 May 2009)

I can't believe people limit themselves to one or the other, you're missing out on some good timbers.
Kiln drying changes the nature of the timber, but as for sucking the life out of it, I think not, I have used hundreds if not thousands of cu ft of kiln dried and air dried oak, I doubt I could tell the difference.
More noticeable to me is European v AWO.

But heyho, if Mr Savage says it, he must be right after all it was in BW.


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## Sgian Dubh (31 May 2009)

Doctor":7tee8io4 said:


> What does "carroty" mean, is it similar to "turnipy"?



Doctor, below is some information from a text I am working on that discusses 'carroty' wood. Slainte.
++++++++++++++++++++++++++++++++++++++++++++++++++ 

Brash wood has a variety of related names including brashy, brashness and brashiness. Additionally this condition is called brittle heart, carrot heart, spongy heart, brash heart, soft heart. Natural brashness or brittleness develops in the living tree caused by the way a tree grows and the stresses it experiences in life. In every case brash wood is weak wood and it unexpectedly snaps across the grain under a load that normal wood of the same species would carry with ease.

Brashness often develops in association with cross shakes as discussed elsewhere. In another instance it develops in exceptionally slow grown ring porous species where the tree lays down a high proportion of soft spongy and weak spring growth, and a low proportion of denser stronger summer growth wood. Ring porous species with unusually narrow year-on-year growth rings are one possible feature to look for; the result of this is that the wood is also likely to be exceptionally light for its species, and this serves as an indicator of potential brashness.

Conversely very quickly grown conifers also lay down much weaker lighter spring wood than they lay down denser and stronger summer wood and this too is brashy. Juvenile wood also tends to brashness, especially if it has grown fast with widely spaced growth rings. Unusually dense reaction wood in coniferous trees known as compression wood is often brash, and this type of wood is not used in furniture, but carvers and turners may well come across it (Hoadley, 2000, p9 99-100). Shield (2005, p 133) discusses brittle heart or brashness being the result of growing stresses within plantation grown Eucalypts where he notes that successive growth increments develop tensile stresses in their length with each successive growth increment developing slightly more tensile stress than the previous year’s growth. To compensate for this the tree develops longitudinal compression stresses towards the tree’s core. Brashness is also caused artificially when wooden artefacts are subjected over time to high heat “such as wood ladders used in boiler rooms.” (Rossnagel, Higgins and MacDonald, pp, 43- 44).

The lesson for woodworkers is that brash or brittle wood should not and cannot be used for load bearing structures, eg, floor joists, floorboards, table and chair legs, rails, etc. The safest thing is to not use it at all except for purely decorative items such as small carvings or other non-critical parts. Secondly, materials other than wood might be better choices in high heat environments such as forges, certain areas within commercial kitchens or glass blowing workshops for shelving, steps, ladders and so on.

*References.*

Hoadley, RB, (2000) _Understanding Wood: a craftsman’s guide to wood technology_, revised edition, The Taunton Press, CT, USA.

Rossnagel WE, Higgins LR and MacDonald, JA, (1988) _Handbook of Rigging for Construction and Industrial Operations_, 4th ed, McGraw-Hill Professional, New York.

Shield, ED, (2005) _Plantation Grown Eucalypts: Utilisation for Lumber and Rotary Veneers—Primary Conversion._ Economic Forestry Associates, Australia. Seminário Internacional de Utilização da Madeira de Eucalypto Para Serraria, pp 133- 139


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## Doctor (31 May 2009)

Interesting and very knowledgeable, "carroty" is a new one to me. However I am not a great reader of woodworking material. I personally would have described AWO as carroty due to its colouring, I call it ginger, but I suppose thats racist these days.
Can I invent a term for the soft brown / white squishy bits which can be found on occasions in ash, "bananary".
Feel free to use it in any work and I allow the term to be used in BW if wanted


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## Mr T (31 May 2009)

Hi

I think Yetloh has summarised the problem with air dried. To use it commercially you need a lot of pace to store it. Anyone who has visited the Barnsley workshops must be impressed by their storage sheds. However most small makers do not have the space. Yes, good air dried is wonderful to work, especially walnut, but practicallity means we used kiln dried. 

I find the kiln dried oak from John Boddy's in Boroughbridge works well.

Chris


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## custard (31 May 2009)

I prefer air dried...provided it really is _dried_!

Most of the complaints about air dried on this thread seem to be about timber that was sold as air dried, but actually wasn't. 

IMO you shouldn't use air dried timber unless you've got either a good moisture meter or a good and trusted supplier, otherwise you're just guessing and hoping for the best.


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## OPJ (31 May 2009)

I'm not sure I've actually worked with truly air-dried timber yet... I usually buy all my wood from Interesting Timbers near Bath. Only time I look elsewhere is when they don't have it in stock! Generally, the quality of the stuff I've had from them has been very good. Most of their stock is claimed to be air-dried but I think that, like a lot of other yards, it's spent a small time in the kiln towards the end of the drying cycle, if only to bring the moisture content down a few weeks early so they can start to sell it and satisfy demand.

I think that regardless of whether the timber you buy is air or kiln-dried, it's important to understand that when you cut in to a wide board, it's going to have a higher moisture content on the inside and you should be aware of that when working it.


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## Philly (31 May 2009)

I've had good experiences with air-dried stock. It's definitely more pleasurable to work. Mind you, most of the lined stuff I've had has been good.
Sadly, I've also had some horrible kiln dried timber - from pieces that are full of checks and cracks through to pieces that are just plain horrid . I'm sure its down to the speed and skill with which the timber is kilned.

Personally, whatever the timber, I try and store it in my nice dry workshop for at least a year before using it - some of my boards are going on six years old now. Makes a big difference.

Hope this helps
Philly


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## Calpol (31 May 2009)

This is going off on a bit of a tangent, but I once got some black walnut (kiln dried) and it had a really horrible smell to it. I can't really explain it, but something like manure if I remember right. Anybody had any experince like that and could shed some light?


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## custard (31 May 2009)

Calpol":fmvpl5zj said:


> This is going off on a bit of a tangent, but I once got some black walnut (kiln dried) and it had a really horrible smell to it. I can't really explain it, but something like manure if I remember right. Anybody had any experince like that and could shed some light?



Faced with a complex glue-up, with the Tite-Bond setting rapidly on a hot day, then my workshop often gets that exact same smell.

:shock:


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## Sgian Dubh (31 May 2009)

In the UK you'll never buy wood that has been air dried outside that is below 17% MC, and 17% MC is a rarity, it's more likely that it's going to be closer to 19 or 20% MC, and all dependent on the season. 

If it's been air-dried in an open ended or sided shed you might occasionally find some that is down to 14 or 15% MC. If it's been air dried outside and subsequently placed in a dry outbuilding or storage place you'll sometimes get air dried stock at about 12% MC.

In all cases you will almost certainly have to further condition air dried material to reduce the MC prior to using it for internal furniture.

My experience and research tells me that decrying the qualities of either air dried or kiln dried wood and claiming that you will only use one or the other exclusively is a wrong decision. There is a place and use for both types of seasoned wood. For instance, it makes no sense to make garden furniture, gates, external joinery, etc out of kiln dried stock that is still at 7 to 10% MC. It's generally more expensive and you need to acclimatise it to exterior conditions before you make the furniture or joinery. Slainte.


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## Sgian Dubh (31 May 2009)

Doctor":wmo2e2yg said:


> Can I invent a term for the soft brown / white squishy bits which can be found on occasions in ash, "bananary".



I'll stick to calling it the traditional name of "slightly rotten", as that's probably what it is, ha, ha. Slainte.


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## Doctor (31 May 2009)

Sgian Dubh":w8zrzekf said:


> Doctor":w8zrzekf said:
> 
> 
> > Can I invent a term for the soft brown / white squishy bits which can be found on occasions in ash, "bananary".
> ...



I think bananary has a nicer ring to it


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## Ironballs (31 May 2009)

I don't have enough experience of air dried to comment, I've used some but not much. I will echo the comments about importance of skill in kiln drying though, chap at the college had a board of 3" oak in that had so many checks in it you could have slapped a sticker on it and called it tartan


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## Sgian Dubh (1 Jun 2009)

Ironballs":2s0qanpg said:


> I don't have enough experience of air dried to comment, I've used some but not much. I will echo the comments about importance of skill in kiln drying though, chap at the college had a board of 3" oak in that had so many checks in it you could have slapped a sticker on it and called it tartan



Not all checks are the result of improper drying. Some checks are a natural result of stresses in a living tree and occur before the tree is harvested. In other words the weakness and fractures, possibly invisible to the naked eye, are sometimes present in the wood before it is dried, and drying it simply reveals the weakness as visible checks or splits.

It is a quite common, but erroneous belief, that air dried wood doesn't suffer seasoning faults. It does. I have seen all the seasoning faults commonly put forward as being primarily a result of improper kilning show up in air dried wood. These include the usual suspects such as sticker stain, end checking, surface checking, case hardening, reverse case hardening and honeycombing.

In the end poorly seasoned air dried wood is as bad for woodworking as improperly kiln dried wood. There are plenty of people out there that can screw up the drying of a stack of air dried wood, and they don't even need a kiln to make the mother and father of a pig's ear of the job. Slainte.


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## BradNaylor (1 Jun 2009)

So as I suspected, it it not a case of one method of drying simply being 'better' than the other.

I have obviously been very lucky in my purchases of KD timber over the years. I have very rarely ever encountered any of the defects outlined by Richard as being popularly attributed to poor kilning. I have to confess though, as someone who makes little use of hand tools, that the subtle variances between the respective working properties as described by Rob sail over my head somewhat!

Ultimately, I am not that interested in the 'working properties'. What matters to me is the appearence of the final piece of furniture, the happiness of the client, and most importantly the profit I have made on it. 

From the point of view of a jobbing furniture maker like myself, rather than a creative 'artist' like the Mr Savages of this world, kiln dried timber will always have distinct attractions. It is normally ready to use virtually straight from the timber yard; no-one I know has the time, space, or money to be conditioning the air-dried timber required for their next six months worth of work in conditions akin to those in a centrally heated house.

I am sure that top quality air-dried timber is lovely stuff. Like most things in life however, compromises have to be made. Kiln dried timber is a compromise that makes my job possible.

And if you know where to look, some lovely wood comes out of kilns.

Cheers
Brad


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## Sgian Dubh (2 Jun 2009)

There is an important characteristic of wood movement to take into account for creating furniture parts, and this relates to the choice made between using air dried wood or kiln dried wood. To set the scene consider the following.

A solid wood panel made up of edge jointed narrow planks, e.g., a table top, raised and fielded panel in a frame, cabinet top, etc., will experience tensile stresses across the wood grain and the joints as it shrinks and, conversely, compression forces as it expands.

The cross grain structure of the wood, and the joints, are both better able to survive under compression forces than they are under tensile forces. In this case a table top glued up of planks at about 13%MC during construction will shrink when put into drier RH conditions. A typical house in the UK exhibits about 40%RH during the winter. This equates to wood eventually reaching about 7.5% EMC. The panel is therefore at some risk of splitting as it shrinks.

On the other hand consider the case of a glued up panel made with planks that are 7%MC at the time of making. During the summer, when internal UK house RH values are approximately 60%, it will expand as the wood moves towards 11.5%MC, which represents its EMC at that RH. Here, the joints and grain experience compressive forces, which are less likely to cause grain or joint failure. 

Subsequently the panel will experience seasonal change over its entire life and will expand and contract to suit. The tensile forces and compression stresses within a panel will alternate as the seasons pass and it settles into a routine where the joints are usually able to withstand these stresses and survive very well. But, importantly, joint failure during the first year of an edge jointed panel’s life in service tends to happen most commonly when the wood shrinks after construction rather than when it expands. As a general rule of thumb it’s safer to glue up wide panels of very dry wood (6% - 7%MC) than to use damper wood, e.g., 12%- 15%MC. Slainte.


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## Ironballs (2 Jun 2009)

Worth knowing, really do think I should get a moisture meter


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## Anonymous (3 Jun 2009)

A new term of reference?

Wood snobery? :lol:

Never had a problem with kiln dried and can't say I noticed any differences or improvements with air dried. 

Wood is wood is wood and you get good or bad regardless of the drying mechanism - it is (was) a living, organic and dynamic material and the *original tree has more impact* on the appearance and 'workability' than the drying!


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## Paul Chapman (3 Jun 2009)

Tony":2wcl9grz said:


> Never had a problem with kiln dried and can't say I noticed any differences or improvements with air dried.



You've probably just been very lucky....... :wink: 

Cheers :wink: 

Paul


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## Sgian Dubh (3 Jun 2009)

Tony":1zzwyv99 said:


> A new term of reference?
> Wood is wood is wood and you get good or bad regardless of the drying mechanism - it is (was) a living, organic and dynamic material and the *original tree has more impact* on the appearance and 'workability' than the drying!



Not quite true in all cases Tony. For instance, if you are heavily into steam bent wood incorporated into your furniture using sawn kiln dried wood will always leave you frustrated and disappointed. It's brittler and stiffer, and the grain runs off at inconvenient angles. 

You get much better results with riven or cleaved green wood, in this case wood that has never been seasoned; but after the bending there's a lot of shrinkage and distortion likely to occur. 

The generally accepted best compromise is to use riven wood air dried to something near or slightly above 20% MC as this gives the best of both worlds, ie, relatively easily bent, and any major drying faults are likely to have showed up by that point of the drying process. Slainte.


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## promhandicam (3 Jun 2009)

Richard,

Thank you for taking the time to post your thoughts on this subject - your posts are easy to understand yet very informative. 

Much appreciated, 

Steve


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## newt (3 Jun 2009)

Yes Richard, thanks for taking the time.


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## moz (3 Jun 2009)

I've just had to return a batch of kiln-dried oak to the timber merchant and thought I would share. I agree that defects can happen with both air dried and kiln dried timber but kilning seems to me to be a much more complex business.











AIUI differences in drying cause differences in colour. The timber would have been air dried to a degree, with the outer few millimetres developing the darker colour but with the core still at a MC of probably above 40%. Putting it in the kiln at this point and raising the temperature to try and compensate leaves the centre white. Maybe someone else understands the chemistry better than me but I know that the colour reaction happens higher up the moisture content scale and stops happening when there is not enough moisture left for the reaction to proceed. 

This is a particular b*****d because, unless you notice the tell-tale stain on the end grain, it suddenly materialises in the form of patches and streaks just as you begin to approach dimension. From the merchant's point of view, the problem is invisible. They replaced without quibble so it's been expensive for both of us. 

I don't know about other timbers but I much prefer air-dried oak if I can get it, but you do need a moisture meter. I remember a few years ago planing up some 3 inch 'air-dried' oak which was practically splashing me in the eye and which subsequently distorted beyond recognition. 

John


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## Sgian Dubh (3 Jun 2009)

John, what you show may be something to do with the tannin found naturally in oak which reacts in the presence of water and ferrous compounds (iron) and produces brown staining. This well known reaction may also be a red herring in seeking a cause for what you show because if you take a white oak or European oak and stick a piece in some hot or boiling water in a non-ferrous container you get water that turns brown just like brewing tea in a teapot, and tea has plenty of tannin in it. 

What is going on during seasoning is that as the wood dries the wetter core transfers water towards the intermediate zone which then transfers the water to the shell and finally the moisture is relaeased from the shell to the air. 

From this point I am speculating, but it is well known that heat commonly speeds up chemical reactions, and if there is brown tannin stain transference from the core towards the shell, the higher heat of a kiln might intensify the residual staining towards the shell.

I don't know if you've ever looked inside a kiln that is used regularly to dry white oaks or European oaks, but I have, and nearly all the exposed surfaces are covered in a brown tannin stain forced out of the oak, as in the snap below. The attached photo was taken about twenty minutes after a batch of oak was removed from the kiln, hence the steam you can see. Slainte.

PS. What does the letterisation AIUI mean? It's irritating me that I can't guess, and I'd like to know!


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## Chems (3 Jun 2009)

As I understand It.


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## moz (4 Jun 2009)

Richard, I know what you mean about tannin/iron stains but this is something different. It isn't a chemical reaction to metal nor is it a fungal stain. I don't know what the technical name is for it but it results from differences in drying speed and temperature. Let's say, for example, that this timber was air dried too quickly in warm weather to the extent that the outer fibres dropped to a MC of 35% but with the centre nearer to 60%. Then the lot was stuck into a kiln at a high temperature till an average MC of 10% was achieved. What people refer to as 'enzymatic oxidation reaction' i.e. the reaction which alters the colour of the timber is happening at sharply different rates and degrees in different parts of the boards. I don't know how common this is but I have seen it before from a different supplier and have had the opportunity to observe some examples over a couple of years. The contrast in colour doesn't diminish with age and I think can be regarded as permanent. I would hazard a guess that most people would see that typical streaking and assume that it was either a feature of the living tree or of the fallen log. However, the shots of the end grain I posted show how the 'stained' portion is contained within the centre of each sawn board. My point is that, although there are problems and necessary precautions with air-dried timber, the complexities seem to really pile on when you get into proper kiln drying, as this particular fault touches upon.

John


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## Sgian Dubh (4 Jun 2009)

moz":k0bctnez said:


> ... the complexities seem to really pile on when you get into proper kiln drying, as this particular fault touches upon. John



John, you might find the discussion linked to below of interest. The author, Eugene Wengert is a renowned authority o. timber technology and kilning issues. I'm not sure the answer to your original question is here, but it's worth a read in any case; or more precisely perhaps, it's worth a read to me because of my particular interest in the subject of timber technology as a sideline to my main interest in furniture design and making. Slainte.

http://www.woodweb.com/knowledge_base/C ... umber.html


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## newt (4 Jun 2009)

John, I have seen those effects on Euro KD oak, although not quite as severe. At first you can mistake it for sap wood when it is on the edge.


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## motownmartin (4 Jun 2009)

I am confused because I found some of the same markings in air dried, unless I was told some porkies.


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## moz (4 Jun 2009)

Thanks Richard, very interesting. the problem obviously has some chemical origin but the 'stains' don't really match any of the descriptions there or anywhere else I have searched. The outer part has obviously changed colour but only to the extent that it looks like any other dried oak. The centre has an almost bleached appearance, as Pete says almost the same as sapwood. However, it must be somehow related to the section on 'chemical stains' - quote:"Chemical stains develop when naturally occurring chemicals in wood react with air (an enzymatic oxidation reaction) to form a new chemical that is typically dark in color". But presumably the normal darkening one would expect as oak dries is also as a result of this reaction. Once the MC has fallen below 40%, the reaction slows and stops. So, in my example, the centre has remained a lighter colour at the point it entered the kiln and fairly rapid drying seems to have kept it so. I would describe it more as a lack of staining but I could be wrong. The timber merchant was familiar with it and said it was related to incomplete air drying in a warm environment followed by kilning quickly at a relatively high temperature. Both examples I have seen, and also Pete's above concern European oak so perhaps climate is a factor. In any case, reading your link, there seems to be so many inter-related factors, who knows?

John


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## Sgian Dubh (5 Jun 2009)

Chems":19xvzez1 said:


> As I understand It.



Ta. Slainte.


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## Sgian Dubh (5 Jun 2009)

moz":1sr54ys7 said:


> In any case, reading your link, there seems to be so many inter-related factors, who knows?
> John



I am intrigued by the phenomenom your photographs illustrate. I don't know the exact cause but if time allows it I'm likely to sniff about until I find what it is. If I do find out I might even add another small section to the timber technology manuscript I am working on. Slainte.


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## OPJ (8 Jun 2009)

Sorry for bringing this thread up again but, I wanted to ask what people thought of what's been happening to some of my 3" beech left overs.







The three lumps pictured here have been sat in my garage, no heating or anything. One on the left had some splits when I bought it. Those larger splits on the right-hand one were also quite visible at the yard. The middle lumps' gone a bit crazy though, with splits running down most of the 3ft length... :?

I assume this is air-dried; what do you think? All I've done so far is to remove the waney-edges and give it a quick belt-sanding for a better look at the surface. My apologies as I know this photo' isn't great. 

This kind of thing has happened to most of the 3" beech I bought for my workbench, although these three are possibly the worst of the lot.  Actually, I've since put most of this back through my bandsaw to try and cut out most of the splitting.

Next time, I might try sealing the ends before I start machining, even though this stuff was seasoned... What do you think?


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## motownmartin (8 Jun 2009)

Olly, I had a load of Yew that I resawn after a few weeks three quarters of it was only fit for the fire, this was air dried.


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## moz (9 Jun 2009)

Hi OPJ. How do you know your beech was seasoned? I'd say it was pretty wet to have lost so much width to the point of splitting when bringing it inside. A moisture meter is the only way to be sure. I bought a Wagner a few years ago after a few disappointments with supposedly air-dried timber (actually hardly dried at all - unscrupulous b*****d). It takes a lot of the guesswork out of it and at least it lets you know how best to proceed. Sealing the ends would have helped but, if it was too green, drying should have continued outside with plenty of ventilation and protected from rain. 

John


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## dicktimber (9 Jun 2009)

In one of the mags this month a guy shows how he made a huge thick table for a customer.
He had the material supplier KD the timber below normal moisture standards.
The reason was to counteract the effect of movement and splitting in a centrally heated house, which is usually the main reason KD timber is preferred.
But never the less you can still experience problems.

Mike


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## OPJ (9 Jun 2009)

Hi moz,

The only truly green timber my preferred supplier sells if oak for framing; the rest of their hardwood stock is all properly seasoned (usually air-dried; sometimes, there's a little kilning towards the end of the drying cycle). I do have a cheap little moisture meter, which reads (on average) 2-3% higher than the £200+ plus meter we have at college. When I got my beech indoors, it was averaging between 16% and 17% on the meter (which could have meant a maximum of 15%).

I started cutting up the timber as soon as I got it home and, from the big stack of wood that spent two weeks indoors (it's only for a workbench...), there was barely any change in the number of or length of splits. The three lengths in the photos above were all left in the workshop/garage and have spent NO timber indoors. Yet, they appear to be the worst of the lot...

I guess it would pay to buy a "proper" meter in the long run :roll: but, I think I also did myself a favour in roughing out the components early on... Otherwise, it may have all ended up looking like those boards above! :shock:

Next time, I'll repeat the same process but will also try sealing the ends. What do you recommend? I know Chestnut sell an "End Seal" product specifically for 'turners but, I've also heard of people using watered-down PVA?

By comparison, the 2" and 1" boards I bought are absolutely fine. I have a dining table to make soon that requires 3" English Oak for the legs - I've learned a lesson here but, I need to get it right next time!! :shock:


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## Sgian Dubh (9 Jun 2009)

OPJ, it is hard to say what the cause of the splits is, but it's noticeable that the splits in the middle and right hand piece are radial. The heart of the tree is towards the bottom of each board in the picture.

One possibility is that the boards dried quite fast in the early stage causing radial surface checking as the drying shell shrank around the still wetter and full size intermediate zone and core. The medulla are lines of weakness and these are most likely to be the location of surface checks in tangentially cut boards.

Later as the intermediate zone and core lose moisture and they too shrink the surface checks in the shell can close up so you can't see them.

Later again, and a bit more drying too, you'll sometimes see those original surface checks open up again, and sometimes, once the surface checks get going in this later stage they just keep on opening up.

Of course without knowing all the circumstances with your wood and not having it front of me to examine closely, I am making what I believe are informed guesses. However, I have outlined a set of circumstances, the responses you can get in wood, and the checking that can result if things don't go just right.

One other scenario that comes readily to mind is that the splits really have little or nothing to do with the seasoning. It could be that the tree had developed structural stresses due to the circumstances it experienced in life; cutting it into boards simply allowed the stresses to work themselves out as checks and splits as the wood dried. Slainte.


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## Ross K (9 Jun 2009)

It depends on the application of the wood...

You want dry wood - it has to be kiln dried, realistically*

You want wood that's "fairly" dry** go for low moisture content air dried.

You want wood for outdoor funiture, go for air dried*** or green.

* Say 10% moisture content. Air dried wood at this level is rare. There is nothing wrong with properly kilned wood.

** For interior applications where the construction method allows for the expected movement, I've used up to 18% or even higher with no issue.

*** 20% plus as a rule of thumb or anything up to green (70%+)


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## Ross K (9 Jun 2009)

As for that beech...

Some trees produce wood that tends to split. Some produce wood that doesn't split. Sometimes it's because the drying is too fast or unevenly, but not always.

Sometimes it just splits because it just does and there's no analysing that can explain it - trees are different from one another!


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## OPJ (10 Jun 2009)

Richard, thank you for sharing your knowledge on this subject. 

Next time I but air-dried timber this thick, _I will_ try sealing the ends to prevent moisture coming in/escaping... My suspicions are that this could be prohibitive to the drying process in not allowing as much moisture to escape...? What would you suggest? I'd be very interested to hear your thoughts.


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## Anonymous (10 Jun 2009)

Sgian Dubh":3bfag1p0 said:


> Tony":3bfag1p0 said:
> 
> 
> > A new term of reference?
> ...



Fair comment Sgian. I have only steam bent wood once and have no experience of how differently dried samples behave when steamed


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## Sgian Dubh (10 Jun 2009)

Olly, out there amongst wood drying businesses there are fans of end sealing and conversely there are those that consider the financial gains through additional usable wood are too limited to bother with the expense. 

So, without getting into a debate on the commercial factors regarding whether or not to end seal here is what I think. To dry freshly felled green wood in a reasonable amount of time for your personal use, rather than drying wood for sale, I think you should take into account the season when you sticker the wood up. You are looking to create a moisture gradient in the wood that gets the moisture out fast enough so that it becomes usable reasonably quickly. Sticker the wood up in late autumn and leave the ends unsealed because relative humidity (RH) is high. If you sticker it up in spring then use the end sealer because RH is lower during spring and summer.

RH and heat, plus air movement are the keys to how fast wood dries. A low RH, eg 30%, and a high heat, eg 35ºC, and fast air movement sets up a steep moisture gradient and dries wood quickly. The trouble is this could easily result in inducing drying faults in air dried wood. Here in the UK we never see such conditions and typical summer average numbers are 60% RH and about 16ºC. Winter sees 80% RH plus, and about 5ºC.

It doesn't look to me from your question that you plan to dry your own wood from green. It seems you are more interested in acclimatising already air dried wood ready for your own use. Air dried wood in this country seldom gets below about 19% or 20% MC. If it is below that it's because it's been air dried in an open sided shed, or it's been air dried outside and later brought into a shed. In your case I would simply sticker up any wood you buy in a reasonably dry environment for some months before you use it, eg, in a dry garage or shed. You only require to lose about 6 or 7% moisture before the wood reaches the sort of moisture content that is at the top end of the suitable range for building furniture destined for indoor use, ie, around 12% or 13%. 8% to 10% is really the ideal range for that purpose, but you can work it cautiously if it's a little wetter.

I don't think there is much benefit to be gained with end sealing if you're drying wood from about 18% to 20% MC down to 10% or 13% MC. It's at the initial green condition, ie 30% + down to about 18% MC that I think end sealing is likely to be most beneficial. Slainte.


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## Ian Fraser (21 Jun 2011)

I have recently joined the forum and have yet to explore it thoroughly. I am teaching myself wood bending, steam bending, and hot pipe bending. For this I need air dried timber, ideally. Can forum members suggest suppliers to get air dried wood from, particularly in the north of Enngland?


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## promhandicam (21 Jun 2011)

Welcome to the forum. Probably best to start a new thread about steam bending rather than resurrect one that is two years old :wink:


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## Sawyer (22 Jun 2011)

This is a very interesting thread. There is lots of folklore on the subject and non-woodworkers speak almost reverentially about 'seasoning' without any real notion of what it means. 

As woodworkers, what we need is the hard science behind this subject. Thanks for the pointers already in this thread and I'd really like to know more. Anybody able to recommend any books or other sources which really get down to the scientific nitty-gritty?


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## yetloh (22 Jun 2011)

Welcome to the forum.

Undertanding Wood by Bruce Hoadley is the standard work on the science of wood for woodworkers and is quoted a number of times in this thread. It is American so some of the terminology is slightly different from what is generally used over here, but you won't find a better, more approachable book on the subject.

Jim


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## AndyT (24 Jun 2011)

You can read quite a lot of Hoadley's book here:

http://books.google.co.uk/books?id=...understanding wood&pg=PP1#v=onepage&q&f=false


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## Sawyer (24 Jun 2011)

Jim, Andy,

thanks for that, Hoadley sounds just the job. I'll take a look.


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## Sawyer (1 Jul 2011)

Thanks again for the recommendation; whereupon I went on Amazon and bought _Understanding Wood _, which arrived yesterday. It looks excellent and I think I'm going to benefit greatly from reading it. 

Great forum too, by the way. Also of much benefit to me and no doubt everybody else who participates.


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## Mr T (7 Jul 2011)

Ian Fraser":veop9cxn said:


> I have recently joined the forum and have yet to explore it thoroughly. I am teaching myself wood bending, steam bending, and hot pipe bending. For this I need air dried timber, ideally. Can forum members suggest suppliers to get air dried wood from, particularly in the north of Enngland?



You could try Nidd Valley Sawmills near Summerbridge. You could call in and see me in Blubberhouses on the way if you do.

I tend to use KD exclusively, mainly for economic reasons eg lack of space for storage, concerns about getting AD down to correct MC in time for the job etc. However I do have some walnut drying in my garden, I end sealed the boards and have had almost no end shakes.

Chris


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