Waterproofing marine ply....suggestions please

[Javelin]

I've just finished replacing the lower support structure and associated bulkheads on a Southerly 115, but could easily be used for flooring etc.
The old plywood was sheathed but you only need a small hole that bilge water can get in and then it all just soaks up the water like a sponge.
Instead of just replacing the ply I decided to laminate my own boards using 10mm Nidaplast as a core.
Two layers of 250g chopped strand mat on each side is enough for a board stiffer than the same thickness ply, will never rot and quite a lot lighter.
If you need a nice smooth finish then just add a layer of 150g cloth.
I'll cover using it in March or April PBO if interested.

 

[Little Dorrit]

Lord - people get so het up... ....

The original post asked:

... So my question. Would you use epoxy to protect/coat the ply...

I think all I was trying to say was that the general consensus was that it was it was not necessary or that most people would probably not use epoxy.

 

[Rum Run]

I've just finished replacing the lower support structure and associated bulkheads on a Southerly 115, but could easily be used for flooring etc.
The old plywood was sheathed but you only need a small hole that bilge water can get in and then it all just soaks up the water like a sponge.
Instead of just replacing the ply I decided to laminate my own boards using 10mm Nidaplast as a core.
Two layers of 250g chopped strand mat on each side is enough for a board stiffer than the same thickness ply, will never rot and quite a lot lighter.
If you need a nice smooth finish then just add a layer of 150g cloth.
I'll cover using it in March or April PBO if interested.

I'd like to see an article on using Nidaplast since you ask.
I made cockpit floor hatches out of polyester, 25mm Kingspan foam and CSM which worked well and was fairly cheap, but would like to see how the proper stuff works

 

[Poignard]

Lord - people get so het up...

OK so here's my reasoning - the OP asked how to treat the ply, and a number of people responded as I did.. I read the OP's post and clearly his boat <b>is</b> dry if it took 20 years for the ply to become soft as butter... <b>of course</b> the best thing is to stop it getting wet in the first place, but boats still get wet/damp (mine sits in a yard for the winter month and it has no on board heat source the damp has to go somewhere) and a coat of epoxy (in my view, but not yours) is the best way of treating ply to stop it rotting.... purely in my view....

Who's getting het up?

The man asked for advice and he got it. Quite detailed advice, carefully considered and freely given. Isn't that what this forum is for?

 

[Little Dorrit]

Perhaps there should be an option for the OP in ALL THREADS that gives a "I close this thread" option so he/she can take a view of the replies, consider they have enough information... and then take a breath and get on with the job in hand?

 

[Poignard]

Perhaps there should be an option for the OP in ALL THREADS that gives a "I close this thread" option so he/she can take a view of the replies, consider they have enough information... and then take a breath and get on with the job in hand?

Why? Nobody is forced to read what they don't want to.

Anyway, exactly what is it that's bothering you? Is it that some offered differing advice to you or is it that some have suggested alternatives to what the OP said he intended to do?

 

[rogerthebodger]

I'd like to see an article on using Nidaplast since you ask.

A friend of mine fitted out the complete inside of a empty hull/superstructure using Nidaplast

He setup a table of 12mm float glass and a top of stiffened cromadex ( powder coated steel.

He then laminated the Nidaplast with epoxy and woven glass cloth and when wet clanped the sheet between the glass table and top plate.

Once cured he gave it a run down with wet and dry then spray with 2K paint.

The inside looked very nice and the whole boat turned out very light. The only think from my point of view was that it was too white and needed some wood trim.panels to make the boat look warmer.

 

[Fantasie 19]

I'd like to see an article on using Nidaplast since you ask.
I made cockpit floor hatches out of polyester, 25mm Kingspan foam and CSM which worked well and was fairly cheap, but would like to see how the proper stuff works

Me too! That's an interesting alternative... one for the mag series?

 

[PCUK]

Plum has given the exact method. to use. I use West Epoxy and if it needs to be thinner I simply warm it by mixing and then placing the pot in warm water in the sink.

 

[ex-Gladys]

Plum has given the exact method. to use. I use West Epoxy and if it needs to be thinner I simply warm it by mixing and then placing the pot in warm water in the sink.

You need to be very wary about warming epoxy. When epoxy cures, it can go exothermic. I mixed up West in a plastic container - about 250 ml - and after about 90 sec, it was smoking and was thrown into the garden... The plastic deformed... If I do any epoxying now, I generally use paper coffee cups with about an inch or so in the bottom...

 

[KellysEye]

The only marine ply I would buy is this: http://www.dutchmarinepanels.com/panels/marine-plywood/kuiper-marine-plywood-poplar-ilomba.html It is made for yacht builders and is the highest quality.

 

[fisherman]

i'm sometimes suspicious about marine ply. I had to use it for a wheelhouse, SFIA regs, it was the only bit that delaminated. I have a WBP, but not BS 1088, wheelhouse now, since 1994, it has had one bubble. Another boat had a deck of loose square unprotected WBP panels, it wore through but never delaminated. I was told the glue is the same, but there is hardwood in marine ply.

 

[Javelin]

Frankly if you use the best marine ply in the world, all it does is buys you a little more time, it wont stop it rotting if not protected and subjected to wet/damp conditions.

 

[Brent Swain]

That is why I always pefer to use well used ply , as it has been around a long time without delaminating, and is thus well proven ,not something you get with new ply. If you cant do that, then put your cuttings in a bucket of water for several weeks to see what happens.
Here in BC, old fir ply is all fir ,new stuff has only fir outside skins, the inside veneers are alder, or some other far more rot prone wood.

 

[oldharry]

Epoxy or not is up to you, but you still need to deal with the damp problem. Epoxying can actually accelerate the rot if it stays damp. Why? Even minor damage penetrating the epoxy waterproof coating will allow water to enter the ply. Capillary action then draws more and more water in. Because of your expensive epoxy coating it cant dry out again, and damp ply = rapid rot. Paint allows it to dry out again if it gets wet.

Painted marine plywood has an average life of 25 years immersed in water. Damaged epoxied ply can fail within three years. Like others here, my floorboards are over 45 years old, and are almost as good as new. Painted both sides, and care taken to protect the end grains.

'Proper' marine ply, not the rubbish that is so frequently marketed as marine grade has all the laminations made of the same hardwood as the facing ply, and all laminations are of equal thickness.
If they are not all equal, and made of the same material throughout then its not marine ply. There is also a specified maximum void width where internal veneers join. Plywoods sold as 'marine' rarely meet these standards nowadays. BS1088 means nothing with foreign imports. its probably the makers stock number! The BS is generally thought to mean male bovine excrement....

 

[Brent Swain]

Perhaps the ultimate solution is to make them out of foam cored fibreglass, altho I find the 20 or so years they last doesn't make it worth the effort; yet.
After two boats with the tiny peekhole liftout panels in the floor and under the bunks, I have switched to making the whole floor and bunk top one big lid, which can be tied down in rough weather at sea . Much quicker to build, much better access for finding things and cleaning, and far more practical all around.

 

[Brent Swain]

Epoxy or not is up to you, but you still need to deal with the damp problem. Epoxying can actually accelerate the rot if it stays damp. Why? Even minor damage penetrating the epoxy waterproof coating will allow water to enter the ply. Capillary action then draws more and more water in. Because of your expensive epoxy coating it cant dry out again, and damp ply = rapid rot. Paint allows it to dry out again if it gets wet.

Painted marine plywood has an average life of 25 years immersed in water. Damaged epoxied ply can fail within three years. Like others here, my floorboards are over 45 years old, and are almost as good as new. Painted both sides, and care taken to protect the end grains.

'Proper' marine ply, not the rubbish that is so frequently marketed as marine grade has all the laminations made of the same hardwood as the facing ply, and all laminations are of equal thickness.
If they are not all equal, and made of the same material throughout then its not marine ply. There is also a specified maximum void width where internal veneers join. Plywoods sold as 'marine' rarely meet these standards nowadays. BS1088 means nothing with foreign imports. its probably the makers stock number! The BS is generally thought to mean male bovine excrement....

Fir is considered a softwood. The all fir older plywood had none of the fast rot problems they now have with far more rot prone inside veneers of "hardwoods" like alder.

 

[Brent Swain]

Perhaps the ultimate solution is to make them out of foam cored fibreglass, altho I find the 20 or so years they last doesn't make it worth the effort; yet.
After two boats with the tiny peekhole liftout panels in the floor and under the bunks, I have switched to making the whole floor and bunk top one big lid, which can be tied down in rough weather at sea . Much quicker to build, much better access for finding things and cleaning, and far more practical all around.

The nice thing about making the lid the entire floor, is it makes it extremely easy to replace them. It also lets you take your floor out and, on the dock or in the shop, put whatever covering you want on. It also makes cleaning and painting the bilge very easy.
A half inch layer of closed cell back packers foam on the underside, can reduce bilge condensation by up to 80%.

 

[Deepankar Choudhury]

Plywood is a significant and constant building material, made up of many different veneers glued together at right angles. These layers offer dimensional stability but leave the edges, which expose all of the wood flooring sections, particularly vulnerable to water damage. This technique for waterproofing plywood edges is especially valuable for healing revealed cut edges of commercially finished phenolic faced plywood boards, such as Buffalo Board™