Epoxy coating ply

Fantasie 19

Fantasie 19

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Just about to do some new cockpit hatch covers - I have West System Epoxy in the cupboard, the hatches are cut, what do I need to be watching out for, any hints or tips?

Is epoxy over the top for this job?

Thinned mixture to better help soaking in on the edges?

I want to be able to do the whole board in one go - hang it from the ceiling using a sacrificial screw/hook?

How many coats?

I'm off to do some googling but I thought I'd pick your brains as well... :encouragement:
 
Fantasie 19 said:
Just about to do some new cockpit hatch covers - I have West System Epoxy in the cupboard, the hatches are cut, what do I need to be watching out for, any hints or tips?

Is epoxy over the top for this job?

Thinned mixture to better help soaking in on the edges?

I want to be able to do the whole board in one go - hang it from the ceiling using a sacrificial screw/hook?

How many coats?

I'm off to do some googling but I thought I'd pick your brains as well... :encouragement:
Click to expand...

Epoxy is very good for this but you will need to paint or varnish over the top as epoxy has very poor uv resistance.
Do not thin it and apply two coats, maybe three on the edges. Watch the temperature requirements as stated by West and the temperature needs to be of the ply and the epoxy, not just the room temperature. If the temperature of the ply raises during application and before the epoxy sets you will get lots of minute bubbles from the expanding air coming out of the wood.

Www.solocoastalsailing.co.uk
 
You may want to consider using peel ply on top as it reduces the chances of amine blush and gives a better finish for overcoating with UV resistant paint or varnish.
 
If you gently warm the work, the epoxy will get thinner and penetrate better.
Sometimes the cooling air inside the work can even pull the epoxy into the grain.

I find it hard to brush epoxy on things hanging, so maybe I would screw in some wood screws on the underside, to form 4 legs for it to stand on.
OTOH it may be better to do one side and the edges, then later the other side plus edges, as the edges will benefit from two coats, while on good ply, one coat is probably enough for the face?
 
Are you just "painting" epoxy onto the wood or laying cloth and epoxy like a stich and glue dinghy?

I only ask as I'm about to make some myself and I'm interested in the best way, I assume it's not best practice to just to varnish the ply?
 
Yellow Ballad said:
Are you just "painting" epoxy onto the wood or laying cloth and epoxy like a stich and glue dinghy?

I only ask as I'm about to make some myself and I'm interested in the best way, I assume it's not best practice to just to varnish the ply?
Click to expand...

I'll be painting it on, though I toyed with the idea of using some tissue for the edges but will settle for an extra coat on the edges as per the suggestion above..

Thanks guys.. very much appreciated..

If I don't use peel ply (thanks for the hint Tranona) what's the best way to prepare the surface for painting when I've finished?
 
Be aware of the moisture content of your ply. That is of significance to the 'mechanical properties' which will be locked in by 'flow-coating with epoxy resin.

It is also helpful to good resin penetration if you warm the ply before application of the epoxy, thus ensuring the ply is cooling down as the resin is brushed on. That ensures resin is drawn into the cut cells of the surface wood - which is what you want. Source - Geugeon Brothers book.
 
zoidberg said:
Be aware of the moisture content of your ply. That is of significance to the 'mechanical properties' which will be locked in by 'flow-coating with epoxy resin.

It is also helpful to good resin penetration if you warm the ply before application of the epoxy, thus ensuring the ply is cooling down as the resin is brushed on. That ensures resin is drawn into the cut cells of the surface wood - which is what you want. Source - Geugeon Brothers book.
Click to expand...

Top tip.... I'll make sure I store them upright on top of the radiator before I coat... :encouragement:

You're comment about damp was also apposite as it was something I was worried about as the ply was stored in the garage, so once I cut them I'd already bought them in to the house to dry out - they've been in the airing cupboard for a couple of weeks now - looks like I was right...
 
I've built a couple of ply / epoxy boats, and I wouldn't, these days, use epoxy coating on anywhere that is subject to wear or chipping, because it's so difficult to top up.

For brightwork I've gone over to Woodskin, which is easy to patch up, so the patching-up is more likely to happen.
 
Polyester might have been OK in the early Mirror days, but most would not use it now. Unless for an experimental cheepy design.
Epoxy is pretty expensive, but not in the scale of things when building a boat. I happened to have lucked into a 200lt drum, so not so worried right now :o
 
Polyester was known as the boat killer in the days of aging m/ply boats. It sticks to start with, but rarely stays put. I've seen it starting to detach within a week of application. The high moisture content of rotting ply didn't help either!
 
The best technique I've found for flat surfaces is not to paint, but to use a flexible plastic scraper type tool. Its what a professional boat builder showed me. You pour a small pool of mixed resin onto the surface and in a few seconds you can spread if over the whole board. You do need to lay the board down and do one side at a time.

For the edges, get a supply of small disposable paint brushes (1/2 inch or 1 inch) and cut the bristles down to only about 2 cm long so you gat a short bristled brush. Its MUCH easier to stipple the resin into the edges. Works for epoxy coating small areas too.

Two coats minimum all over and then watch that you seal the holes where you put any fastenings. A little wax on the screw and then drip a tiny bit of resin in the hole is another trick. Dip the screw/bolt thread in varnish is another trick. If you ever want to remove the screw, apply a soldering iron to the screw to warm it up first.

You'll need to makes sure you abrade/wash off any amine blush between coats (if you get any) Sometimes I've got away with no blush at all. Peelply is a good idea but ideally needs vacuuming onto the surface and that gets tricky. You might get away with rolling it on?

edit: I agree that overcoating with a UV proof finish is essential - as others have pointed out.
 
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Yellow Ballad said:
What did you go for in the end?

Is polyester resin a no no for sealing ply? It'll be painted with Hempel light primer, would this be ok on it's own?
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I have found polyester resin easier (as well as a lot cheaper) to work with than epoxy. It is far more tolerant. A few years back I built a yacht tender out of polyester sheathed exterior grade ply, and painted with B&Q exterior gloss over primer. It lasted 8 years (when I sold it), during which it was used a thousand times, with no signs of separation or other problems apart from wear on the chines which was easily patched up.
 
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I did this with my locker lids and I wish I hadn't :) ! Varnishing is a cathartic, spiritual job, epoxying is a horrid, acrid and fraught job, with amine blush, contamination, the horror of potentially water getting under the epoxy after it has gone off. Even after you have got it right, if UV does penetrate it it will go cloudy and look shocking... I won't be epoxying them again :) (probably more down to my own lack of skill than any clearer reason...)
 
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