green oak decking

[johnnyb]

i am currently constructing a timber deck with a timber building i have had the joists cut and treated. i am just thinking on deckboards and cladding. a very good merchant called h.venables is not far from me and they specialise in oak. they have priced up oak 6 by 1 at £18 m2 BUT this is green oak that i would have to plane myself probably only a mornings work for the amounts involved. what are the negative aspects of using green oak will it look terrible and split disintegrate. will it plane up ok on a sedgwick pt260. should i add some grooves, how should i treat it if at all. i will definitely buy air dried cladding but cant decide on the decking.
john

 

[MikeG.]

Johnny,

I am a big fan of green oak, and use it a lot. However, I think it would be a complete disaster in these circumstances.

It will shrink up to about 10% in width, it will twist, split and stain. Occasionally, it will even stick sharp spikes out where it splits. Whatever you leave it looking like, however good a job you think you've done, you will be called back again and again to put it right. Just as an aside, you would probably have to use stainless steel screws too.........green oak eats normal coatings and mild steel for breakfast!

Mike

 

[jasonB]

I used green larch for the deck in my garden and left it with the sawn finish off the bandsaw mill. Its not too rough to sit on and is anti-slip. Its weathered in to exactly the same colour as the framing which was green oak.

If you do go as you suggest then 25mm PAR will possibly be a bit on the thin side and as others have said will move & shrink. You will also want to give your machines a very good clean out after as any damp oak shavings will make any steel/iron rust.

Will track down a pic and post later.

Jason

 

[jasonB]

Couple of pics of the newly fitted deck, I had the boards cut to 100x32, was abouy 1/2 to 2/3rds the cost of similar size oak

And the same deck after about 12months natural weathering, I did not treat the wood as there was a risk of any chemical leaching out and dripping into the pond filters that are below the deck

Jason

 

[wizer]

that garden is absolutely beautiful!

 

[johnnyb]

thanks for the replies, i love the deck jasonb! the company also has air dried at a slight premium. i think this would be the more reliable/ predictable choice. what sort of % moisture would be termed air dried i was thinking 20%. am i right in thinking that green oak would be 40-50%. i was going to use stainless screws with the bit of thread near the top as these look quality(spax). i think that inch boards would be fine planed down to 3/4. i have 5 litres of double boiled linseed oil in an ancient tin i was thinking of using this on the boards and on the under timbers. one advantage of using oak like this is you can machine the profiles, balusters, rails etc yourself and not have to pressure treat them as any body whose raised a deck will testify the deck boards trend to be cheap its the rest of it that costs! how durable is european oak and how could i make it more durable(if thats possible) without adding a film finish. maybe 50/50 tung oil and linseed treated yearly?

 

[jasonB]

Whatever you try to coat it with it will still age, the finish will just make it age in a blotchy way, personally I would just leave it a bare wood.

Whatever stainless screws you go for just watch the torque setting on your driver as stainess screws will snap a lot easier than the plated steel ones

I'm also not keen on any type of groove to the boards, it traps dirt and moisture which then leads to moss/algee growth

Jason

 

[RogerM]

That's a stunning garden Jason - and that decking compliments the pool perfectly. Also love the variety of surfaces - paving, brick, gravel, pebbles, plus of course the decking. Add the variety of foliage with those lovely Acers and it looks like a piece of heaven. Who's the gardener - you or SWMBO?

 

[jasonB]

We all do a bit in the garden. The maples were at their best a week or two ago with the altumn colours, leaves have started to drop now but some of my bonsai are still looking good.

Jason

 

[wizer]

I want to get a lot more maples in my garden. I spent the garden budge on bamboo this year. Next year it will be maples, I love them.

 

[CWatters]

I had bamboo in last garden put in by previous owner. I like it but never again as it spread too easily - even under a concrete path and up on the other side. Ended up getting one bed professionally dug to try and get rid of it. Love Maples though.

 

[chipchaser]

Hi John,

Sounds like you have a nice job there. I see you have had useful replies to your post and hope the following comments might also be helpful:

I was professionally involved with the repair of the south range of Little Moreton Hall, not far from Biddulph, in 1990 using all green Oak. You should be able to see which pieces were replaced and judge for yourself how it has fared after 18 years of exposure. Much of the rest of that range dates from about 1520 IIRC and, where not continually damp, has lasted very well. The north range is older still. Most of the defects leading to repair of the south range were decay in bressumers around blind mortices at the bottom of posts. The water drained into the mortices where it was trapped allowing decay to progress.

It isn't possible to give an accurate estimate of green or air dried moisture content. You need to measure samples or ask Venables to take readings. However, these may vary especially if the 6x1 has been recently resawn to that size. Venables used to offer kiln dried Oak also but maximum thickness was 3". I expect it would be very expensive and have no advantage for outside use.

You could expect the timber to stabilise at about 16% in use if clear of the ground, designed to allow rain to shed and ventilated to allow drying. Note that this will vary seasonally.

You should expect green Oak to shrink and twist. Those that appreciate this will like the end result but those who expect precision joinery may be disappointed. On another job I saw ledged and braced green Oak doors where the movement of the Oak had snapped off brass screws holding the boards to the rails. Also expect some staining where run off from Oak passes over other materials, especially metals. Your client needs to be advised what to expect.

Movement along the grain will be small whereas tangential could be large with radial somewhere in between. On a timber framed farmhouse where we replaced a principal post with green Oak the post shrank 1" on the exposed face in 6 months. I don't have details to hand but expect that post was about 8" square.

If possible design the deck to accommodate movement of the timber as it dries and avoid joints which rely for their appearance on tight well fitting surfaces. For example a tusk tenon can be tightened up after the beam through which the tenon passes has shrunk. Design to avoid water traps so joints can drain and dry out. Oak is very durable as long as not continually wet.

I believe Larch is reasonably durable as it is used for roofing shingles.

Brass and stainless steel fixings are both ok for Oak, s/s being much tougher. Plain mild steel will be attacked by the Tannic acid which helps to give Oak its durability resulting in unsightly black stains and failure of the steel. I wouldn't risk treated mild steel fasteners. Even if the coating is resistive it may corrode if breached by mechanical damage during construction.

I like the silvery appearance of weathered untreated Oak and personally don't think that any paint or stain finish is worthwhile. For many years paint manufacturers would not recommend any of their coatings for use on Oak as they could not guarantee a reasonable life. Some of the modern coatings may be ok subject to the manufacturers advice.

All the best and look forward to seing pictures when you have done!

Graham