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biglicker

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Hi, I have to replace some boards on the cabin of my boat and I was wondering if anyone had ever used MDO in an exterior environment. A freind told me MDO would be better than marine ply and it is cheaper too. They will be painted after fitting.
Can anyone advise me,


thanks....
 

treds1

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Is this for internal or external use?

I replaced some paneling (internally) in my parents boat with WBP ply after doing a scouring the net for info and it was suggested as suitable for above the waterline use.
 

Phil Pascoe

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You don't need to scour the net for wbp - all builders merchants keep it. It'll delaminate quite quickly if any edges are left open to water - make sure everything cut is lagged in waterproof glue or something. Marine ply is better, but it's a LOT more expensive.
 

biglicker

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Hi, the boards are for external use, I've not heard of MDO before but was told it is water resistant and will do the job ????
 

vally bar

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I would of thought it ok for fresh water but suspect for salt water,
as that is what marine ply is specificly designed for.
 

marcus

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I would have thought all things been equal it would be better in salt water as salt water is wood's friend — the salt is quite a good preservative which is why timbers on seagoing boats tend to last a lot longer before rotting than freshwater ones.... It's the topsides of boats (where rain is getting in, not salt water) that are the most susceptible. Although to be honest any kind of wooden boat is madness really :) Unless you love to spend all your free time painting...
 

jasonB

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MDO is not that widely available here, more an American board.

For those that don't know its Medium Density Overlay, sort of MDF faced ply.

J
 

vally bar

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I always thought the salt attacked the glue in standard ply and that marine was made with a diferent formula.
 

marcus

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As far as I know (someone correct me?) both marine and wbp are glued with urea formaldehyde. The difference lies in the quality/durability of timber and quality control in laying up the laminates. Marine ply should have no voids at all in it, as water can wick through to them and rot can start. Particularly round the edges. WBP has loads of voids.
 

Stormer1940

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To be honest i think I would just stretch the boat out (pardon the pun) and go with marine ply.... You have to ask yourself the question of if you want to be replacing things sooner in the future?
 

vally bar

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Many years ago (say 10 or 12) we made floats to float cables across a river/ inlet? Near Selafield for a company called Land and Marine, the spec was Marine ply, I suggested that we could make them cheaper in WBP and was told that they would be used more than once and due to it being salt water it had to be Marine. If any body needs any CNC work doing give me a pm as we have had a large order canceled and have capacity.
 

marcus

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According to Wikipedea....

Marine plywood is manufactured from durable face and core veneers, with few defects so it performs longer in humid and wet conditions and resists delaminating and fungal attack. Its construction is such that it can be used in environments where it is exposed to moisture for long periods. Each wood veneer will be from durable tropical hardwoods, have negligible core gap, limiting the chance of trapping water in the plywood and hence providing a solid and stable glue bond. It uses an exterior Water and Boil Proof (WBP) glue similar to most exterior plywoods.
Personally I think that the thing about salt/fresh water is a bit of a red herring. Its not like if you were building a plywood boat for freshwater you would make the hull out WBP!

If I was using ply on any exterior part of boat I would definitely grit my teeth about the cost and use marine ply — its such a harsh environment for timber, and any corner cutting will tend catch you out, usually sooner rather than later. Most economies on boats are false economies in my experience....

All this puts me in mind of the old sailing joke that, as a pastime, boating is comparable to squatting in a cold shower being sick while tearing up fivers....

Regarding WBP it has always seemed to me that it is a bit of a flaky specification for plywood anyway. Quite literally the test is to boil it in water and see if it comes apart. How often does anyone actually do that in real life?! Ok so it shows it probably wont delaminate which is something, but the test in itself says little about its resistance to rot.
 

Jake

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marcus":3ez7xve7 said:
As far as I know (someone correct me?) both marine and wbp are glued with urea formaldehyde. The difference lies in the quality/durability of timber and quality control in laying up the laminates. Marine ply should have no voids at all in it, as water can wick through to them and rot can start. Particularly round the edges. WBP has loads of voids.
I think both are resorcinol formaldehyde (RF) rather than UF - I can't be bothered to check so I may get pulled up on it, but the dark glue line certainly suggests it.
 
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