Wood treatment & drying times..

[ellal]

Having got my workshop built last year, with a lot of great help from here, I thought I'd build a slightly smaller shed this year to a similar design. All has been going well (and much quicker due to learning from previous mistakes), but I seem to have come a cropper with the shiplap -again..!

I got a similar batch (19x125 quality pine), and had it vac treated. It was done in a few days, and I've since left it 10 days before putting it up. Now last time, I got 'shrinkage' along the whole length of each panel, and was advised that I'd used it too quick.

However, this time I've found a different problem. Over a length of 2.7m the middle is 2/3mm 'thicker'. And over the height of the walls (22 layers), that adds up to either a 4-6cm bend, or a gap of 2/3mm at each end.

I went to the supplier to see if it was a batch problem, but their pre-treated stuff was OK. So I'm guessing it's got to do with the ends drying out quicker than the middle. But how long should it take for the whole lengths to dry out?..and what/where is the best drying method?

Cheers.

 

[big-all]

this is why i asked for an untreated "sample" so i would know when the treated shiplap was fully dry

it should be air dried with spacers between each individual plank
if i remember correctly i came unstuck after drying in my house for 14 days

it shouldnt be any different over its lenght as the wood is only 9mm thick [unless you tryed to dry the bundles without spaces ]

measure it against the cladding on your other shed to see what the dry size will be if i remember i allowed 111mm it actualy came out at 108mm plus 2mm to allow for wet weather expansion so a coverage off 110mm

 

[ellal]

At the ends it's 110mm..in the middle 112/113mm (it's 15mm thick though)

I dried it (or thought I did) with 15mm spacers in between layers.

Is there anything I can do to rectify this, or is this drying process 'damage' problem irreversible?

 

[JohnD]

I've done a bit of shiplap cladding, and I'd say (as it's summer now) leave a bit of a gap between the boards at their max width. Come winter they will swell, and if packed tight may burst off the fixings. I fix mine with scraps of cardboard between, the idea being that when the weather turns wet the cardboard will go soft and be easily squashed or rot away.

BTW to accommodate the swelling/shrinkage I also only put one row of screws or nails in, my belief is that if you put two rows per board, you are encouraging them to split when they get dry and shrink.

Mine is in an exposed coastal area, when the sun gets on it, it really dries and shrinks a lot. I put the waxy stain on (both sides) before fixing to slow down moisture moving in and out.

 

[big-all]

At the ends it's 110mm..in the middle 112/113mm (it's 15mm thick though)

I dried it (or thought I did) with 15mm spacers in between layers.

Is there anything I can do to rectify this, or is this drying process 'damage' problem irreversible?

yeh sorry my mistake ive been using ex 12.7mm by 100mm internal txg today it comes out at 9mm x89mm coverage
the ship lap txg comes out at 12.7

nothing to worry about nothing will be permanantly altered when it all dries to the same mouisture content it will all be the same size

but as said above the 2mm gap is essential
and i would never ever secure an exterior bit of wood in two places as you will get cracking
you can of course hold the edge of one peice with the edge off the other so infact its supported in two places but it can expand and contract freely

 

[ellal]

nothing to worry about nothing will be permanantly altered when it all dries to the same mouisture content it will all be the same size

so let it dry out more before using?

and i would never ever secure an exterior bit of wood in two places as you will get cracking
you can of course hold the edge of one peice with the edge off the other so infact its supported in two places but it can expand and contract freely

Not quite sure what you mean here. each piece is secured with only a single row of screws, but could you elaborate on that last bit..cheers

 

[ellal]

I've done a bit of shiplap cladding, and I'd say (as it's summer now) leave a bit of a gap between the boards at their max width. Come winter they will swell, and if packed tight may burst off the fixings. I fix mine with scraps of cardboard between, the idea being that when the weather turns wet the cardboard will go soft and be easily squashed or rot away.

If I leave a bit of a gap in the middle, each end will have a gap of approx 4mm if I keep the boards level..given that there will be even more shrinkage, won't that mean leaks?..

Interesting about the cardboard - doesn't it encourage water to ingress though (capillary action?)

 

[JohnD]

If I leave a bit of a gap in the middle, each end will have a gap of approx 4mm if I keep the boards level..given that there will be even more shrinkage, won't that mean leaks?..

The shiplap boards overlap each other a bit to keep out the rain (hence the "lap") so that water runs and drips down the outside face. Because the boards will swell and shrink as the weather changes you can't have a tight fit edge-to-edge.

Interesting about the cardboard - doesn't it encourage water to ingress though (capillary action?)

If you were careful enough, you could lie it on the top edge of each board where it will be covered by the next overlap... but it's a wooden structure, it is never going to be a tight seal. Mine is on battens with tilers felt behind which stops draughts and water reaching the inside.

Anyway, the bits of cardboard are mostly gone after a year. You could pick them out in dry weather if you felt like it. If they did get wet then they would fall apart.

 

[ellal]

The shiplap boards overlap each other a bit to keep out the rain (hence the "lap") so that water runs and drips down the outside face. Because the boards will swell and shrink as the weather changes you can't have a tight fit edge-to-edge.

I understand the principle. However, what I found with my previous build was that because they are situated in an area which gets direct sunlight all day, and exposed to the wet/cold weather, then the movement is quite a lot, and I did get water coming in a bit. This one is just a storage shed, so don't want to have felt, as there is no internal lining. With the extra original gap, I'm just concerned that the 'lap' will only just cover...

 

[big-all]

this is why you need a dry sample to let you know when the wood is fully dry

cut off a foot dry it in the direct sun take it in doors at night and after 2 days it shoud be pretty well dry

Not quite sure what you mean here. each piece is secured with only a single row of screws, but could you elaborate on that last bit..cheers

this was more a general "helpfull "comment thrown in for refference

ok with txg shiplap you secure the bottom of the board only this supports the top off the next so its supported in 2 areas but can expand and contract
its the same with fence pannels you must have noticed all the splits on cheap panels because they just fire nails every few inches and each bit that gets 2 nails splits in the summer because it cant move

it would be the same with your shiplap if you screwed the top and bottom
you wouldnt get cracks appearing through shrinkage but you may get cracks as the wood expands and is forced forwards or backwards

 

[ellal]

I've been fixing the shiplap with a single line of screws approx 2cm up from the bottom.

With the current problem, would it be OK to fit the boards now, starting from the middle, and allowing the gaps at each end - and then expecting the middle to also contract over time? Or should I leave them until they're are all fully dried out which may take some time (I've had to fill the kids playroom with spacers between the boards)?

 

[ellal]

Thanks for all the advice...put the boards up, and it's all equalling out nicely.

cheers