Timber movement

S

Steviecracknell

Active Member
Joined
7 Apr 2010
Messages
50
Location
Greenock, river Clyde
Visit site
I have just finished gluing up my oak and walnut cabin sole 6mm thick laminated overlay. If your a wood butcher Like me, then you may be concerned about expansion of the wood across it's width, even though it's quarter sawn, and to be stuck down with west epoxy. The question is, would it be prudent of me to leave 6mm on either side were the laminate hits the sides of the quarter berths, or would it be ok to fit the laminate tight to the sides. If I leave an expansion gap, this would be filled with sika flex, but would possibly detract from the overall finish.
I want to fit it tight, but mighty regret it, as I know the kind of damage expanding timber can do. Fitting it next week, size is 2200mm long by 800mm wide.
 
I'm not a wood butcher like yourself, but what would make your laminate expand? If it's heat, warm it up before cutting to size. If it's humidity (more likely) soak your wood before trimming. Then you don't need any Sikaflex ... ...
 
Presumably it is on ply which will make it very stable. There may be some differential expansion between the oak and the walnut - you don't say whether they are edge gled or caulked - but with an interior panel that is not subject to extremes of temperature and humidity unlikely to do anything. Worst that can happen is glue lines breaking or slight ridges at the joints.
 
Tranona said:
Presumably it is on ply which will make it very stable. There may be some differential expansion between the oak and the walnut - you don't say whether they are edge gled or caulked - but with an interior panel that is not subject to extremes of temperature and humidity unlikely to do anything. Worst that can happen is glue lines breaking or slight ridges at the joints.
Click to expand...

if the wood takes up moisture, it will expand.
the ply will not stop it expanding, the panel will go convex rising in the middle
 
sailorman said:
if the wood takes up moisture, it will expand.
the ply will not stop it expanding, the panel will go convex rising in the middle
Click to expand...
That really depends on how thick the ply substrate is. An internal panel like this is unlikely to suffer from differential expansion of such thin section laminates. If they are only 6mm thick then the ply substrate should be at least 9mm, probably 12mm.
 
Tranona said:
That really depends on how thick the ply substrate is. An internal panel like this is unlikely to suffer from differential expansion of such thin section laminates. If they are only 6mm thick then the ply substrate should be at least 9mm, probably 12mm.
Click to expand...

ply does not expand across the panel width
solid timber will expand on water absorption so will bend the ply
 
Short answer.
Dont spoil the ship for a happorth of epoxy!

If you seal the edges and bottom face of the ply before varnishing, all will be fine.
In fact WEST is an acronym for Wood Epoxy SATURATION technique.

What tranona says is correct, re warping, but once any glue lines break, you've undone all that beautiful work, so why risk that. After all, all it takes is one wave down the hatch or one spill...And oak looks awful once black staining creeps up the end grain...

Personally I would leave a 2mm gap all round and fit ( say) 30 x 5mm vertical edging battens all round. After all, boats do flex a bit anyway..:)

Edit: Re Sailorman. 5mm over ply is pretty thin stuff. Posh job tho innit! 'One day' I am going to have solid 150 x20 bare teak cabin sole, ah, one day..
 
Last edited:
sailorman said:
ply does not expand across the panel width
solid timber will expand on water absorption so will bend the ply
Click to expand...

You are correct. Solid timber can expand and contract. Just that the likelihood internally is minimal, particularly in small sections such as the OP is using. Would not use the same method externally without good protection to keep moisture out.
 
Tranona said:
You are correct. Solid timber can expand and contract. Just that the likelihood internally is minimal, particularly in small sections such as the OP is using. Would not use the same method externally without good protection to keep moisture out.
Click to expand...

we had some solid oak ledged & braced internal door supplied early, the builder stored them in a barn.
in less than 2 weeks some had a 12m/m bow across the doors where the timber expanded & bent the 175 x 25 rails
 
Sailorman is right, surface treatment is unlikely to prevent the movement across the grain which is the result of changes in humidity. You need to design for it or the resultant movement will soon wreck the finish. The kitchen table I am sitting at, I made 40 odd years ago and it has been compressed with tie rods and coated over and over again but still opens up every summer. Even laminate flooring which is comparatively inert has to have an edge space. Shame to go to all the trouble and have to repeat it after a couple of years.
 
I can only speak as I find. I laminated teak strips onto ply using epoxy, including "grouting" the seams with thickened, pigmented epoxy for cockpit seats more than 20 years ago. There is a cockpit cover, but otherwise they are exposed to changes in temperature and humidity all year round. Not a sign of movement and every glue line intact. No protection other than a couple of goes when new with Deks Olje D1 - not repeated as did not seem to do anything.
 
The movement figures for quarter sawn oak and walnut are very similar. If the timber was bought as kiln-dried you could probably expect the moisture content to be around 12%, give or take. On a cabin sole this will obviously increase to who knows what, but if it went up to 20-25% you could expect around 14mm of expansion over an 800mm width (assuming it isn't constrained).

If it is bonded to a stable substrate then what happens is either the wood is compressed, or the the whole panel bends, or a mixture of both. Compressed wood takes on a permanent set, so when (or if) the wood dries again to it's initial 12% it will crack along the grain.

You have some options open to you:
1. Laminate the underside of the ply with similar thicknesses and species (called a balancer). That will prevent bowing.
2. Condition the wood you intend to use by leaving it in the cabin for a few months. This will ensure that any movement after laying and bonding will be reduced to the minimum. (too late for you to do that now!)
3. Coat the wood with a non- or low-permeable finish. This will slow down the rate of movement and should therefore reduce the actual dimensional change.
4. Rout a gap lengthways between each of your laminates and fill the gaps with Sikaflex.

Since you've already made up the panel, I would stick a balancer on the back, cut it to leave a good 6mm gap along the long edges and give it several coats of varnish or Osmo PolyX on both sides. Keep an eye on the 6mm gap for a few months and then decide whether to disguise it with a cover strip, an upstand (ie like skirting board) or fill it with Sikaflex.

Most people won't even give it a second glance, but they will definitely notice if it is bowed.
 
Ply not included

Cheers to everyone for the great responses. I have decided to fit the panel tight to the sides of the 1/4 berths. The thickness will remain 6mm, against my better judgement. I know the expansion rates, so thanks for that, but i've never experienced or indeed known anyone that has laminated and glued this combination of woods to a timber surface, or any other surface. So basically what i'm saying is. if you don't try it, you'll never know!! or nothing ventured, nothing gained....

Stevie.
 
The emc where aI live is probably around 17%, so I recon the timber has reached its max natural expansion. On the other hand, if soaked, then dried, it would possibly move, fingers crossed it doesn't.
Its getting stuck on Saturday, and won't see the sea until next season.

Stevie.
 
You must log in or register to reply here.

Share this page

Top