Air dried oak for outdoor chairs?

[Deadeye]

I've drawn up my plans and cut my templates.
So I have run out of displacement activities and have to commit to buying timber.
Outdoor chairs - I'm thinking air-dried (no point in kiln dried I guess?) and oak (as they'll be out in all weathers; with an Osmo UV finish. Is that sensible? I've never done outside stuff before. I have seen comments about iron and oak so will be careful re. screws.

As any timber is going to have to be delivered (I need about 15 cubic feet all told), any recommendations for source? I've a couple of quotes at £50-60/cubic foot (for 1" and 2" waney slabs); what's the goinig rate?

Finally, what about glue? Cascamite or something better?

I'm going to do a prototype in pine to try to make sure the design works and weed out the worst of my mistakes!

Any other advice glady received (apart from "go to Ikea" perhaps).


Thanks!

 

[bjm]

I get all my hardwoods from Chilworth Timber - based in Milton Common, just off M40 - very friendly to deal with.

 

[marcros]

you could look at (sweet) chestnut too- might be a bit cheaper than oak, but it is very dependant on what you can get locally. I was looking to make an outdoor table and chestnut was certainly cheaper but nobody kept it locally.

 

[Oddbod70]

I've just finished repairing a old bench seat with some air dried oak that I felled and planked about 3 years ago. So yes, air dried is fine - as long as it really is dried. Get it from a reputable source.

the wood will move a little as the seasons change, but most designs allow for that. Plenty online, just go for one you like.

Osmo is good, but can take for ever to dry - It took weeks for my bench seat to dry. Put one coat on now and you might get the second on in spring! The issue may well have been me tho. Maybe just an oil finish (eg teak). Whatever I'd put a few coats of a preservative on first. It does make a difference.

I use polyurethane glues, but anything waterproof should be OK.

 

[Cabinetman]

Hi Deadeye, I’m hoping that price includes VAT, otherwise it’s a little bit on the high side, especially for Waney edge.
How about American Ash, comes rough sawn square edge at about £30 a cubic foot plus VAT for 2 inch, One of my favourite timbers to work – doesn’t cause many problems lol.
That’s quite a lot of timber, how many are you making?

 

[bjm]

...How about American Ash....

Only problem with Ash is that it isn't durable..........and don't get sucked into the air dried vs kiln dried debate. The wood will acclimatise to it's environment.

 

[Cabinetman]

Not sure why you think it isn’t durable, it’s been used for tool handles, sports equipment, outdoor garden implements, boatbuilding and cart wheels for years. Well that’s what it says in my bible, I just looked it up to be sure. Ian

 

[Oddbod70]

this is one of my favourite ever charts.

Massive credit and thanks to the wilddeckcompany.co.uk for putting it up on their website. Hope they don't mind me putting it here

 

[bjm]

Not sure why you think it isn’t durable...

From a preservation perspective it is classed as non-durable. Given the OP says the chairs will be out in all weather the legs will become susceptible to decay as they are more likely to wick water from the ground. Ash is OK to use where it only gets intermitently wet (and subsequently dries) or is saturated - decay fungi take about 7-10 days to become established and will only tolerate a narrow band of moisture (~20%).

Thanks OddBod, I was looking for that chart.

 

[Cabinetman]

Well it just shows what you don’t know doesn’t it haha I thought with it being used for all outdoor type things it would be suitable, but I bow to your superior knowledge gentleman.
Nice chart thanks.

 

[bjm]

These classification are largely based on ground-contact trials and can be taken as advisory if the wood is unlikely to become sufficiently wet to initiate decay, something not always easy to account for?

 

[Doug B]

you could look at (sweet) chestnut too- might be a bit cheaper than oak, but it is very dependant on what you can get locally. I was looking to make an outdoor table and chestnut was certainly cheaper but nobody kept it locally.

Another vote for Sweet Chestnut, I bought a cubic metre of it when Associated timber went bust & have used it for mainly external projects, it looks a lot like Oak without the price tag.

 

[Oddbod70]

These classification are largely based on ground-contact trials and can be taken as advisory if the wood is unlikely to become sufficiently wet to initiate decay, something not always easy to account for?

Yeah, its just a guide isn’t it. I've got windows in my house that are clearly some kind of Meranti and were fitted back in 1982, 4 owners ago. Apart from me fixing a bit of softness around one or two hinges they are absolutely fine.

I guess the message is that in similar circumstances a more durable wood should last longer. I certainly wouldn't use the years given as much more than a guide.

 

[AndyT]

I have made precisely one outdoor chair from air dried oak (bought at Westonbirt Arboretum who have not yet restarted their timber sales as far as I know) and one from sweet chestnut (bought from Wentwood Timber in S Wales). So I'm no help in getting your timber delivered, sorry. But I can confirm that the chestnut was lovely mild stuff to work, looks like oak from a distance and is holding up just fine outside. It also makes the finished chairs noticeably lighter and easier to move around.

 

[Sgian Dubh]

decay fungi take about 7-10 days to become established and will only tolerate a narrow band of moisture (~20%).

I'm afraid that information is not quite right. The only fungus that can establish and sustain itself in timber with such a low a moisture content (~20% MC) is dry rot (Serpula lacrymans). This is why the term 'dry rot safe' is common currency within the timber drying and woodworking community, and also explains why the majority of timber (softwoods primarily) that are kiln dried for the construction industry has a target moisture content of 20 MC ±2%. Not all wood, even that for the construction industry is dried - for example, large sections of oak (4" X 4" and bigger) are quite commonly used for construction purposes that are either green or only partially air dried. All the other fungi that find sustenance in wood require the moisture content to be of a higher percentage, typically a great deal higher, e.g., 30% MC and above.

As I think you were correctly implying in an earlier post, durability from a timber technology perspective has a specific meaning, i.e., the ability of a wood species to resist decay when it's in ground contact, e.g., buried in soil as a fence post. Non-durable species in ground contact typically, in the area in contact with the ground, rot away in less than five years, whereas that portion of the wood not in ground contact will survive anything up to two or three times as long. In other words, the bottom end of a fence post buried in the ground can be expected to rot away much quicker than that part of the post exposed only to air, rain and sun - the fence will fall over because the buried part of the posts rot away. Slainte.

 

[Fitzroy]

Air dried oak near me is £45/ft3 inc VAT. Osmo oil is not supposed to be used on horizontal surfaces if you read the tin. I used it on an oak table, legs are spot on after 4 years, top was knackered after one summer and two winters. I’d go for a team oil that is easy to top up, or just leave them au natural to go silver.

F.

 

[bjm]

I'm afraid that information is not quite right. The only fungus that can establish and sustain itself in timber with such a low a moisture content (~20% MC) is dry rot (Serpula lacrymans). This is why the term 'dry rot safe' is common currency within the timber drying and woodworking community, and also explains why the majority of timber (softwoods primarily) that are kiln dried for the construction industry has a target moisture content of 20 MC ±2%.

I was perhaps being too broad in what I was saying but the generally accepted safe level of moisture to prevent the initiation of fungal decay is <20%. Moisture content once decay is initiated is a different, and complicated matter. There are very few places in the world where wood will reach equilibrium moisture contents of 20%, typical ranges are from 9-16% (protected, outdoors) across the calendar year - Read about it here Other factors, such as ambient temperatures, also play a role in susceptibility to decay. Oak has natural durability and, again, the fact that it starts 'green' is not the finished state.

The only reason to kiln dry to 20% is to reduce costs and to limit drying defects - it's a trade-off. The wood will naturally air dry further and will reduce again in service- 20% mc is not a typical service level for any wood anywhere.

Dry rot is a special case. Firstly, it doesn't like draughts, which is why it is found in un-aerated environments. It isn't a major decay organism to exposed wood. It also differs from other fungi in that it has the ability to transport any moisture it requires from great distances (>100m in extreme cases). The term dry rot is misleading - the fugus raises the moisture content at the point of decay. The term dry-rot safe is even more misleading.

 

[Geir]

I made some Adirondack chairs some years ago out of oak, and a prototype in pine first. A prototype is useful, you'll learn a lot. But oak is very heavy. It became a nuicance to move them around so I changed them for new chairs in western red cedar. As for finish you can use what you like. Sun and rain will do its work. Film finishes will flake in a year or two, and oils will not really give so much protection. So the main thing is that you have to REfinish every other year or so. Or let them get a grey patina. They won't break down in many, many years, regardless of wood species.
Good luck. Garden chairs you made yourself will be a great joy and pride for years.

 

[Sgian Dubh]

... - Read about it here Other factors, such as ambient temperatures, also play a role in susceptibility to decay. Oak has natural durability and, again, the fact that it starts 'green' is not the finished state.

The only reason to kiln dry to 20% is to reduce costs and to limit drying defects - it's a trade-off. The wood will naturally air dry further and will reduce again in service- 20% mc is not a typical service level for any wood anywhere.

Dry rot is a special case ... The term dry-rot safe is even more misleading.

Interestingly Brian, the WT Simpson paper on EMC you pointed me (us?) to is one I'm already familiar with having used it in my own research for something I wrote. Your figures for the EMC of wood in protected external locations, i.e., in a shed or barn for example are pretty much in line with my knowledge or understanding.

As far as I'm aware the primary reasons to kiln wood destined for the construction industry are as you say to reduce costs, limit drying defects (and also limit further drying defects after incorporation into a building's fabric), but it is also to reduce the likelihood of fungal infection prior to selling to the end user. True, in service, wood destined for habitable buildings will lose more moisture with, in the UK, the timber in ventilated roof spaces generally settling somewhere near 18%, and wood inside the climate controlled living or habitable quarters generally hovering somewhere close to 12% MC, e.g., internal walls and floor joists.

I can't argue with your point about dry rot being a special case. We humans have a habit of creating ideal growing conditions for dry rot through the buildings we erect. Dry rot is rare in the wild, and it has a preference for softwoods over hardwoods, so our preference for using mostly softwoods in building construction is an additional factor in favour of its growth once it becomes established.

But I am somewhat puzzled by you saying the term dry rot safe is misleading basically because if the wood is kept dry enough, i.e., at or below 20% MC, then the fungus can't become established. On the other hand, introducing moisture to the wood, such as a leak for example, leads to a situation where dry rot spores can initiate an infestation, after which, as you say, the fungi's hyphae can reach out far and wide, even though brick or mortar to find sustenance. Slainte.

 

[Cabinetman]

Also as far as I know, kiln drying kills any woodworm. Ian