Waterproofing marine ply....suggestions please

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Matata

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Hi all, our boat has/had a ply false floor covered with carpet. Twenty years later it was as soft as butter! The carpet was keeping it together. I have removed the old ply floor and currently in the process of replacing rotten bulkheads etc. I was going to replace it with a proper marine ply floor. What I was going to do was epoxy coat the underneath layer . Then glue/screw it down and then re epoxy coat it again. with final coat of epoxy and grit. So my question. Would you use epoxy to protect/coat the ply. I was going to use thinned epoxy , maybe a couple of coats to seal the end grain. I read on this forum that I think SP do specifically a thinned resin for this task. I bow to your experience and open to suggestions of how you'd do it.. Regards Nic
 
Do you need it to last longer than twenty years?

If not, use marine ply.

If yes, loads of flow coat, more on the edges.

Why are you going to use grit?

Surely carpet is more comfortable?

What is SP?

Tony
 
Why not look at the real problem and keep the cabin sole dry 99.9% of the time?

OTOH, we have a marine ply cockpit sole in an open racing boat, it gets wet with spray and sometimes bilge water. When we're not using the boat, there is a canvas over-boom cover. The ply is just painted.
OK, the boat goes into a shed from December to March. The ply is 10 years old already, no sign of problems.

A cabin sole is relatively easy to replace. Things like wood stringers, ply bulkheads, floors (as in timbers running across the boat supporting the boards) are all structural and much more grief to replace.
 
I would coat the marine ply with epoxy, not thinned, with at least 3 coats on the edges and 2 on the faces. If you are going to screw it down drill and countersink the holes oversize and coat the hole walls with 3 coats too. Make sure all edges are rounded. Do all this at home in a warm place with room temperature epoxy, washing and rubbing down between coats or whatever your epoxy manufacturer says. Let it harden for at least a week before screwing down. Don't apply grit to the epoxy. Lay carpet of choice on top. Will easily last 20 years.

Www.solocoastalsailing.co.uk
 
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lw395 said:
Why not look at the real problem and keep the cabin sole dry 99.9% of the time?

OTOH, we have a marine ply cockpit sole in an open racing boat, it gets wet with spray and sometimes bilge water. When we're not using the boat, there is a canvas over-boom cover. The ply is just painted.
OK, the boat goes into a shed from December to March. The ply is 10 years old already, no sign of problems.

A cabin sole is relatively easy to replace. Things like wood stringers, ply bulkheads, floors (as in timbers running across the boat supporting the boards) are all structural and much more grief to replace.
Click to expand...

+1

My cabin sole is 50 years old. It is plywood painted on the underside and varnished on the upper side and edges. I think you'd do better making sure your boat's interior is dry.
 
SP system polymer. A make of epoxy. I'd like to use marine ply as I hate doing a less than job. I'll worry about in 20 years time! The extra cost of the marine ply and epoxy compared to the amount of time I'm spending on it makes me want to do this as a one off job. Would you be tempted to thin the first coat to help it be absorbed and penetrate better? Ta
 
If you like the look of wood then IMHO marine ply well varnished should be perfectly OK. If you use epoxy it will take you twice as long to do any future rubbing down to bring it back to new. If you use varnish that job will be quite easy and mean you can have a lovely wood floor. When you put the floor down use rivnuts and countersunk machine screws so that any future removal can be done without having to fill and re drill holes.
 
Most of the interior paneling of my 50+ year old plywood boat is WPB. Where it is not varnished or gloss painted for show it is coated with Danboline, including the end grain. Although there is often some water down below because the cockpit is not self draining there is no sign of rot.

With a GRP boat there is no excuse for dampness down below sufficient to cause rot so no need for epoxy coating, nor for expensive marine ply. Stop the leaks if there are any, keep it ventilated and use conventional coatings.
 
Plum said:
I would coat the marine ply with epoxy, not thinned, with at least 3 coats on the edges and 2 on the faces. If you are going to screw it down drill and countersink the holes oversize and coat the hole walls with 3 coats too. Make sure all edges are rounded. Do all this at home in a warm place with room temperature epoxy, washing and rubbing down between coats or whatever your epoxy manufacturer says. Let it harden for at least a week before screwing down. Don't apply grit to the epoxy. Lay carpet of choice on top. Will easily last 20 years.

Www.solocoastalsailing.co.uk
Click to expand...

+1

This is excellent advice, to which I would only add that - if you want to avoid the washing & most of the rubbing down between coats (to get rid of amine bloom) use peel ply.
 
Matata said:
SP system polymer. A make of epoxy. I'd like to use marine ply as I hate doing a less than job. I'll worry about in 20 years time! The extra cost of the marine ply and epoxy compared to the amount of time I'm spending on it makes me want to do this as a one off job. Would you be tempted to thin the first coat to help it be absorbed and penetrate better? Ta
Click to expand...

If you really feel the need to epoxy it, I would not thin the epoxy with solvents, but heat it with a hot air gun (gently!) or heater as you brush on the first coat.
 
Plum said:
I would coat the marine ply with epoxy, not thinned, with at least 3 coats on the edges and 2 on the faces. If you are going to screw it down drill and countersink the holes oversize and coat the hole walls with 3 coats too. Make sure all edges are rounded. Do all this at home in a warm place with room temperature epoxy, washing and rubbing down between coats or whatever your epoxy manufacturer says. Let it harden for at least a week before screwing down. Don't apply grit to the epoxy. Lay carpet of choice on top. Will easily last 20 years.

Www.solocoastalsailing.co.uk
Click to expand...


+1

I replaced cockpit hatches the year before last and just painted them - what a mistake that was... they lasted a season.. next time I did it properly - epoxy coated as per the above, and then paint on top of that... if I got one lesson it was spend time up front to save time...
 
Fantasie 19 said:
+1

I replaced cockpit hatches the year before last and just painted them - what a mistake that was... they lasted a season.. next time I did it properly - epoxy coated as per the above, and then paint on top of that... if I got one lesson it was spend time up front to save time...
Click to expand...


The OP is doing internal work and there is no need to use epoxy to coat ply. The problem is almost certainly leaks which have caused the rot in the ply bulkheads and cabin sole.

Spend the time and effort eliminating the leaks then use conventional coatings.
 
Tranona said:
The OP is doing internal work and there is no need to use epoxy to coat ply. The problem is almost certainly leaks which have caused the rot in the ply bulkheads and cabin sole.

Spend the time and effort eliminating the leaks then use conventional coatings.
Click to expand...
+1 Treat the problem not the symptoms.
 
TQA said:
If warming both wood and epoxy before applying you may need to use a slow cure hardner to prevent the epoxy setting in the pot or stringing as it is applied.

Ask me how I know this.

I recommend the use of a foam roller, just make sure it is epoxy proof.
Click to expand...

I only ever heat the wood, and the epoxy once it's been brushed on.
Only exception to that would be working in very cold weather, then warm the epoxy components to 25deg or so before mixing, otherwise they won't go in the syringes. I stood the cans in warm water for a while.
Warming resin in the pot (epoxy or poly) can cause it set react more quicky, So it gets hotter and reacts even quicker. I have heard of people rushing to apply smouldering resin before it bursts into flame.
 
This thread is becoming a bit of a farce.

As has been said by Twisterowner and Tranona treat the symptoms.

I would guess that most cabin floors have a good bilge paint on the underside and are simply varnished on top.

It will take you just as long to epoxy everything as it will to apply a good bilge paint and varnish. Plus as I pointed out earlier you can keep on top of this with relatively little work.
 
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We all go straight to ply for this sort of work, can't help thinking there's a lot of work being done to make it do the job. Timber will cup, I suppose. Nidaplast might be OK but lots of work also, and how to make good the edges?
One supplier here: https://www.ecfibreglasssupplies.co.uk/category/nidaplast.
I have a toilet cubicle panel liberated from a building site job. It's 12mm thick, very dense, very heavy, hates screws, some sort of resin, still trying to find a use for it. HDPE sheet is expensive.
Some products here:
http://www.bayplastics.co.uk/index.htm
 
paella said:
This thread is becoming a bit of a farce.

As has been said by Twisterowner and Tranona treat the symptoms.

I would guess that most cabin floors have a good bilge paint on the underside and are simply varnished on top.

It will take you just as long to epoxy everything as it will to apply a good bilge paint and varnish. Plus as I pointed out earlier you can keep on top of this with relatively little work.
Click to expand...

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.... :)
 
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