Decks advice

[Tugnut]

Hi all
Im in the process of replacing the plywood decks on the boat with 18mm marine ply, the outerside of the decks will be fixed down and most of the other bits willl be removeble to be able gain access to the bilges shaft etc but would like for some advice on what to protect them with was going to coat the whole board in polyester resin and the tops of the boards with a layer of glass matting the followed by a non slip topcoat but 100% sure the way to go people are saying put some sort of sealent like g4 sealant on first and some say's resin would be ok on its own any advice would be great.

Thanks
Dave

 

[Tugnut]

..

 

[bluemoongaffer]

I'd use a couple of coats of epoxy on all sides, making sure the ply edges are really well coated. You could put glass on as well but not sure it's really necessary. I used Epifanes non slip deck paint on epoxy. Has worked well for me.

 

[Rossynant]

Polyester resin has poor adherence to wood, in comparison to others.
You may use epoxy or polyurethane resins (varnish) - whichever preferred. Both resins will seal the edges OK.

For strengthening the ply - also both. Probably that is not obvious in UK

Epoxy + glass is usually used, but possible as well to use good clear polyurethane, varnish + glass. Same way. Two pack is preferred, as it's clear resin like epoxy, but since this is not structural piece any may do - easier to use one pack maybe.

In my opinion polyurethane is even better. And looks good, has UV filters usually (epoxy needs protecting, disintegrate in sunlight), you will be probably painting with it anyway. With one layer of glass cloth and careful painting the glass is not visible, so it looks just like varnished wood, nice finish.

Standard way, doubling the breaking strength of ply (but that on 8-10 mm, can't recall for thicker) was 2 layers of thin fabric (glass cloth) of about 100g/m2. Glass mat is inconvenient for this and less effective.
Just for surface protection one layer is enough.
For polyurethane also natural fiber can be used, like cotton or flax canvas, and it gives about the same technical characteristics, that is double the breaking strength. Depending on canvas thickness naturally.

With epoxy natural fiber is not so good, may fail.

Hope this may be of help

 

[Tugnut]

That's for that great help

 

[Rossynant]

P.S.
I should add a warning in case you try polyurethane varnishes - well, try first, I don't know UK brands, who knows what their properties are. Done such thing myself, but long time ago. As long as varnish meant for wood - should stick, I guess. Get the hardest kind, especially if only for thin layer. I was using a kind for parquet floors.
Not water-polyurethane of course, not 'oil-modified' - of course any resin varnish can be laminated, as such, so experimenting is possible but I have no idea

Two pack clear is usually just resin, some with solvents (thinners) but this is no problem in thin laminating. Some exist which have additives - to make more 'bulk' with cheaper chemical added, this may have different mechanical properties so see how it goes. Should do as well.

Polyurethane is less penetrating into some woods then epoxy, pine for instance, so this is something to look for, such wood should be sanded more coarse, or resin thinned for first coat.