Shrinkage question?

[agg221]

Well I had a measure up and elected to go for 200mm x35mm planks and we managed to get enough planking to cover the whole 40` trailer out of the one stick. Very little waste ,well chuffed. Just need to see how much it all shrinks in the summer. Is it worth treating this or just leave it alone ?

 

Bob

 

If you can edge out all the sapwood, I would leave it untreated. If you need to keep sapwood in I would definitely treat it heavily - I never find oak sapwood to be at all durable (often just let it rot off before I mill given the choice!)

 

When you bolt down, fit the boards 'frowning' rather than 'smiling' as it will reduce cupping and any that you do get will help water shed between the gaps, rather than pond in the middles.

 

Alec

[PeakOakFrames]

Trada quoted figure for green oak shrinkage is 8% across the face of the timber so about 12mm on a 150mm board. Doesn't make a lot of difference whether it quartered or through and through with the shrinkage.

 

The amount of cupping on each board will matter, quartered boards will barely cup where as through and through will cup. You want to have the heart side of the board facing up from the trailer bed so it will shed water through the gaps not pool in the cupped boards. Through and through boards are stronger than quartered boards due to the orientation of the fibres.

 

Sap wood will rot in very short amount of time as a trailer bed, avoid it as it is easy to spot. I would just lay the fresh sawn boards butted up and let them shrink back, as I said earlier you'll probably end up with 10-12mm gaps between boards if they ever get very, very dry. More likely than not it will be closer to 6mm(1/4" for those of an imperial mindset) as they will never get down much below 18%MC in working life.

 

Finally only use one fixing per board width otherwise as they shrink they may well split. To help avoid this I'd use an oversize hole, say 8mm for an m6 dome head coach bolt.

 

Really wish I had the cash to get a mill, if only I didn't have to actually give the VAT man his money!

[aspenarb]

 

Finally only use one fixing per board width otherwise as they shrink they may well split. To help avoid this I'd use an oversize hole, say 8mm for an m6 dome head coach bolt.

 

 

Thanks to all for the advice on shrinkage , I have now cut the boards at 200mm wide and had intended to anchor them down with the self tapping/drilling countersunk screws. Will one of these in the center of such a wide board keep it down?

 

Bob

http://arbtalk.co.uk/forum/attachment.php?attachmentid=167787&stc=1&d=1414318048

[agg221]

Thanks to all for the advice on shrinkage , I have now cut the boards at 200mm wide and had intended to anchor them down with the self tapping/drilling countersunk screws. Will one of these in the center of such a wide board keep it down?

 

Bob

 

It should, although there is a risk that it pulls through if the board is a long way from quartersawn and trying to cup heavily. Coach bolts would be more certain. You could try a pair of your screws, fairly close together near the centre of the board, say 2" apart so the relative shrinkage of the board in between them is minimised.

 

Don't forget that the board will also shrink in thickness, so you will want to be able to nip them up a bit, probably next summer. It's easy to do this with bolts, rather more tricky with screws as you will have to clean all the heads out by then to get the driver back in.

 

Oh and last night, I should have said 'smiling' rather than 'frowning' ie the bit from nearest the centre of the tree upwards.

 

Alec