How much will new timber skirtings shrink?

[Lobster]

I need to replace a long length of skirting board (3.8m long to be precise) and I'm concerned how much it may shrink having been transferred from the timber yard (ie under cover but open to the outside air) into my centrally heated house. Is there a rule of thumb for % shrinkage and/or how long it will take to equilibrate?

SWMBO's organised a decorator (spit) to come in next Monday, and I only bought the skirting and brought it in the house this morning - does te panel reckon I will be OK fitting it on Sunday?

Thanks David

[Jim K]

solid wood flooring vendors talk about weeks...

Jim K

[newshound]

If it is fixed fairly securely (say, a couple of three inch number eights into good brickwork or blockwork every half metre?) will this prevent it from moving? Same principle as used for continuous welded rail, the friction at the shoes resists any tendency to expand/contract with temperature changes.

[Cash]

It won't shrink in its length - but it will shrink in its width ("sometimes" quite a lot, but you should expect a few millimeters) over a period of time.

Stick it on and hope for the best - but I would suggest you really won't notice any difference until the next time you redecorate.

Cash

[John Rumm]

Most of the shrinkage should be across the grain, so not too much of a problem with skirtings.

[meow2222]

I like to leave the timber there for a month at least before fitting it.

If you need to move quicker, the higher up the fixings go the less the top will move. I'm not suggesting taking this too far though :)

NT

[Dave Liquorice]

That'll be why tracks buckle if there isn't enough gap left between the rail ends at each fish plate joint then. And why welded track has a long tapered, sliding, overlaps to allow the track to move.

Do not under estimate the forces involved with expansion.

As others have said most of the movement in timber will be across the grain not along the length but of course the timber may still cup, warp or twist as it dries...

[harry]

No-one can say. It depends on how much moisture is in them presently, also how they have been cut, what part of the tree and how they were dried in the first place. Best to leave them for a couple of weeks at least indoors to let most of the shrinkage take place before installation.

[Tim Watts]

And CWR (continuous welded rail) is usually stretched as it is clipped in tobuild in some "free" expansion potential.

[polygonum]

With the applied tension depending on the temperature on the day it is installed.

[harry]

You can get non-timber skirting that doesn't shrink at all. About 50% extra cost.

[sm_jamieson]

Like the recycled plastic stuff ? MDF skirting is cheap, but some long lengths at work have had the joints op= en up, so I guess it can shrink also. Simon.

[Lobster]

Good to know, thanks! Actually that ties in with a slatted door I have here, built on-site by a joiner using fresh timber: it quickly developed see-through gaps of about 4mm between each 'plank' :(

David

[stuart noble]

A quarter of one percent shrinkage for each one percent drop in moisture content to be precise. About 3% IME but might be dropping from 17% mc to zero in the worst case scenario.

[RobertL]

and I'm concerned how much it may shrink having been transferred from the timber yard

IME It will shrink across the grain; the length will be pretty much unaffected. In my case the skirting now has a 5mm gap where it meets the floor :-(

Have you considered letting the decorator do his stuff with the skirting off. you can then add it on top of the decorated wall in a few weeks once it has shrunk.

Robert

[SteveW]

In my school days, we had a device in Physics, consisting of a cast base with vertical forks at each end, a large metal bar with a hole through it passing through both forks and a nut on a thread at one end of the bar. The bar was heated to expand it, a bolt put through the hole and the nut tightened so that the bar was in tension between the bolt pressing against one fork and the nut against the other. The teacher would then carry on with the lesson and as the bar cooled and the rod contracted, the bolt would be snapped, with a loud bang.

SteveW