Peel ply on (laminating) epoxy barrier coat?

[dankilb]

I'm grateful for the input on my previous thread on epoxy coating our hull, the gelcoat and outer-laminate of which is has a large number of small blisters:
Gelcoat pox (after blasting) - how to fill and fair before Penguard?

From this I learned the different characteristics of solvent and non-solvent epoxy and it was clear that there would be advantages to us in going for non-solvent epoxy first, to help smooth out the surface and not risk applying heavily solvented coatings to a potentially quite permeable substrate.

I plan to use a laminating resin for this (EasyComposites EL2) as it is significantly more affordable than either West or GelShield Plus. By 'affordable' I mean we cannot afford either of the other two!

My question is, can I apply peel ply on the last coat of epoxy to protect the surface and aid adhesion of the next coat? I have worked with peel ply a lot in laminating applications, so I don't have any questions about its basic characteristics or performance. 500mm rolls are available and should be easy to handle. The cost isn't prohibitive... But I cannot find anything online where someone has used peel ply like this, outside of a laminating/molding application.

Some initial tests suggest it takes EL2 a couple of hours to gel (outside in UK Spring weather!). So the schedule would be: Apply first coat (with brush) in the morning; second coat in the middle of the day, rolled and bladed and/or tipped as required; apply third and final coat at the end of the day, followed by peel ply while still tacky.

My concerns are that then peel ply won't behave as predicted and I could run into messy and costly difficulties! OTOH, my motivations include not having to sand/key the surface before the next coat (42' AWB worth and lots of that directly overhead) and also offering a bit of protection while the stuff cures overnight and then until ready proceed with the remaining coats.

The remaining coats will be a combo of Penguard HB first for adhesion/build and then Jotamastic 87 for additional water resistance. SML have already provided the paint (and confirmed they think it'll work!), so I'm not after suggestions of a completely new product/approach at this stage.

I know this is a more complex schedule than standard, but I've got the challenge of a) loads of tiny blisters, b) lots of small voids in the hull laminate/resin I want to protect from future osmosis, c) only myself and first mate available as 'skilled' labour for any hot coating.

TIA!

 

[Hacker]

I can’t see why that wouldn’t work. Mads (SailLife) used peel ply when he was redoing his hull. It stops any amine blush and allows you to put the next layer on without sanding. As long as you are doing the next layer within 24hrs then you will get primary bonding.

 

[Rhylsailer99]

i painted the bottom 12" of my bilge keels with west system epoxy then the next day i started the painting with the 1st bottom coat with penguard HB all seems ok fingers crossed its bonded well.

 

[dankilb]

I can’t see why that wouldn’t work. Mads (SailLife) used peel ply when he was redoing his hull. It stops any amine blush and allows you to put the next layer on without sanding. As long as you are doing the next layer within 24hrs then you will get primary bonding.

Yup, I thought the exact same re: Mads. He did apply a layer (or two?) of glass in the process though, so technically the peel ply was still going on top of laminate. I cannot see any reason that resin (without wetted glass) should perform hugely differently, especially as the previous coats will have gelled by the time the peel ply is added. But then again, I wonder whether the peel ply might become a bit too saturated with resin and/or end up removing a load of the resin and film thickness unncessarily?

i painted the bottom 12" of my bilge keels with west system epoxy then the next day i started the painting with the 1st bottom coat with penguard HB all seems ok fingers crossed its bonded well.

Yeah Penguard is the b****x isn't it - sticks great to anything. I actually asked SML 'why Penguard, why not Jotamastic?' and they said nothing adheres better to GRP/gelcoat than Penguard and nothing does a better job of building up even layers/film thickness.

So I've got full confidence the whole lot will adhere together (unless we do something really stupid!). But I just don't want to have to key the surface! We've had the hull blasted and it left behind the most perfect substrate for paint. But without peel ply, the laminating resin will turn that into a glossy mirror! Know it only needs a key, but there's a lot of area and the design of the boat means much of that area is directly/horizontally overhead while you're crouching or squatting underneath!

 

[TernVI]

With no glass or carbon in there, I think the peel ply will squish liquid epoxy to zero thickness in places and you will get a wrinkly mess.
Getting peel ply onto epoxy that's no longer liquid but still tacky sounds dubious. It will stick when you don't want it to, and maybe not do any good as the air has already had a good go at the epoxy surface.

Peel Ply, in my limited experience is all about squeezing the resin and letting the air out. It compacts the resin down onto the glass or carbon. The carbon stops it being compacted any further.
I've only ever used it with cloth in the resin under it.
I'm happy to learn that I'm wrong in this matter.
Maybe a small scale trial might be a good move.

The only boat I've had epoxied, they put glass cloth in there, it seemed to work. Not sure what the current thinking is.
I suspect it's a good way of getting depth of coating relatively quickly? A layer of wetted glass cloth is more stable than just wet epoxy? I don't know how viscous EL2 is, but the kind of wet film you get brushing epoxy tends to be pretty thin compared to glass cloth?

 

[dankilb]

With no glass or carbon in there, I think the peel ply will squish liquid epoxy to zero thickness in places and you will get a wrinkly mess.
Getting peel ply onto epoxy that's no longer liquid but still tacky sounds dubious. It will stick when you don't want it to, and maybe not do any good as the air has already had a good go at the epoxy surface.

Peel Ply, in my limited experience is all about squeezing the resin and letting the air out. It compacts the resin down onto the glass or carbon. The carbon stops it being compacted any further.
I've only ever used it with cloth in the resin under it.
I'm happy to learn that I'm wrong in this matter.
Maybe a small scale trial might be a good move.

The only boat I've had epoxied, they put glass cloth in there, it seemed to work. Not sure what the current thinking is.
I suspect it's a good way of getting depth of coating relatively quickly? A layer of wetted glass cloth is more stable than just wet epoxy? I don't know how viscous EL2 is, but the kind of wet film you get brushing epoxy tends to be pretty thin compared to glass cloth?

Yeah, a wrinkly sticky mess is what I'm worried about!

I'm pretty confident that it would preserve the film thickness of the previous coats that had 'gelled'. Once they've gone tacky (in a 'wet on tacky' or 'hot coat' schedule), they're not going anywhere. Equally, the period between 'gel' and 'cure' should theoretically be fair game for re-coating, including re-coating with the final peel ply layer.

On the other hand, I do agree that the peel ply will take most of the film thickness of that final coat with it. That's potentially around 5L of epoxy together with 100m of peel ply - so not an insignificant value of materials!

I guess the question for me is... If it takes that final coat, but leaves behind the substrate I'm looking for, I'd be willing to consider that worth it for the cost/effort/risk. If it turns into a mess, though, then it'll have been a very costly mistake (and very hard once cured - requiring more of the onerous sanding I'm hoping to avoid!).

I'm not rushing to do this ASAP so I have some time for testing. I've got a scrap GRP water tank I'll try first. If that works, then I might try it on the rudder. I'll of course report back.

What would seal the deal for me is someone coming along who has done this, or seen it done. And if there isn't such a person, maybe that's telling us all we need to know?!