Plywood Vs MDF

[blackrose]

I wonder how many builders/fitters actually do it?

 

I doubt many do - but if a boat's been properly insulated there shouldn't really be any condensation coming into contact with the lining in the first place, although perhaps that's a bit optimistic around doors and windows.

 

My boat is lined in oak faced ply and has two oak faced MDF bulkheads. Although the effect is nice I do sometimes wonder how long the veneer will last? Personally I'd prefer solid wood T&G - even if that meant pine (because hardwood's going to be prohibitively expensive), but everyone seems to like veneered finishes and you rarely find T&G linings on boats these days.

[smileypete]

I was thinking of clear waxing the showing face, would that and a varnish on the back/edges around windows, doors, other holes be suitable?

 

I'd have thought so, though a water based woodstain will dry much quicker than varnish.

 

Edit: I'd consider doing the backs and edges of everything, even flooring.

 

cheers,

Pete.

Edited February 20, 2008 by smileypete

[blackrose]

I'd have thought so, though a water based woodstain will dry much quicker than varnish.

 

Edit: I'd consider doing the backs and edges of everything, even flooring.

 

cheers,

Pete.

 

Pete, how does a woodstain seal wood? I thought it just stained it? Isn't the grain still open after staining?

[tomsk]

I've heard some worrying stories about the dust produced when cutting MDF too, maybe due to the glue used to make it?

 

MDF is banned in septic-land due to dust concerns, it swells and is rubbish for lining out.

 

Ply delaminates eventually but is far more durable in damp surroundings.

[smileypete]

Pete, how does a woodstain seal wood? I thought it just stained it? Isn't the grain still open after staining?

 

Something that stains wood without sealing it is usually known as a wood dye.

 

Wood dyes are usually spirit based which helps differentiate them from wood stains.

 

cheers,

Pete.

[Tim Lewis]

Am I right in thinking you should also always paint or seal MDF when fitting it? It's not just the dust that gives off nasties (isocyanates?) but the very stuff itself. Nice!

 

But a top-end boatfitter I was talking to who also builds luxury kitchens etc said people were generally poorly informed about MDF; that the water resistant stuff was very good and he'd like to be able to use more of it except that it's not liked by boaters. He meant for interior use - bulkheads, cabinetry etc - not lining out.

 

He also said ply lining should be painted/vernished each side so it can't get attacked by condensation/leaks from behind -- but you all probably know that.

 

Not a boat builder but in the construction industry we always ( or should) paint the back of ply/board when applying a finish to the front - it is known as 'balancing'. This prevents unequal warping of the faces. I once worked on an office block where we had to replace all the access panels in the toilets (it was a fifteen storey building!) because the tiles cracked for this reason.

 

Tim

[sueb]

We get loads of condensation and damp floors from the wine bottles!

Sue

[blackrose]

Not a boat builder but in the construction industry we always ( or should) paint the back of ply/board when applying a finish to the front - it is known as 'balancing'. This prevents unequal warping of the faces. I once worked on an office block where we had to replace all the access panels in the toilets (it was a fifteen storey building!) because the tiles cracked for this reason.

 

Tim

 

That makes sense, but why doesn't faced, pre-varnished ply come out of the factory suitably 'balanced'?

Edited February 20, 2008 by blackrose

[ChrisPy]

'warping' of 9mm lining ply is irrelevant because the stuff is so flexible anyway. As long as it is well fixed on battens there shouldn't be a problem, unless it gets saturated. Warping of 18mm ply used in construction is a different matter.

 

(If I recall my schoolboy maths correctly, the resistance to bending is increased by the third power of the thickness, so 18mm ply is 8 times stiffer than 9mm ply).

[Dylan]

'warping' of 9mm lining ply is irrelevant because the stuff is so flexible anyway. As long as it is well fixed on battens there shouldn't be a problem, unless it gets saturated. Warping of 18mm ply used in construction is a different matter.

 

(If I recall my schoolboy maths correctly, the resistance to bending is increased by the third power of the thickness, so 18mm ply is 8 times stiffer than 9mm ply).

It feels eight times heavier too!

[smileypete]

That makes sense, but why doesn't faced, pre-varnished ply come out of the factory suitably 'balanced'?

 

It is, but if the back gets wet (eg though condensation, leaks) it can still warp.

 

cheers,

Pete,

[Big Steve]

That makes sense, but why doesn't faced, pre-varnished ply come out of the factory suitably 'balanced'?

 

I've never seen pre varnished veneered plywood. Where do you get it? I would say it should be balanced, are you sure it doesn't have a matt sealer coat on it?

 

Steve

[blackrose]

I've never seen pre varnished veneered plywood. Where do you get it? I would say it should be balanced, are you sure it doesn't have a matt sealer coat on it?

 

Steve

 

I don't know, I just assumed (perhaps mistakenly) that it could come pre-finished to make things easier - the same way you can buy pre-finished hardwood floors for example.