Varnish does not stick well to epoxy

[dbeck]

We might have an issue with our varnish. As recommended in the manual, we are using one-part International Schooner varnish. So far its applied to transom, hood, rubrails. The varnish should be fully cured by now. However, it does not seem to stick very well. Once there is a small damage, it is not to difficult to scratch the varnish off with a finger nail or to peel it off with two fingers.

I believe we followed the instructions of the varnish carefully. Sanding, cleaning, vacuum-clean the epoxy ... We applied the varnish without thinner and sanded with 240 grid in between the coats.

Somebody of you having similar problems?

Dietrich

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I used Interlux (the USA brand name) Schooner varnish over epoxy on both my boats (my Pocketship and a Skerry I previously made), and it has worked great.
The finish is very tough and shows no tendency to flake off. In fact, it seems tougher and more durable than the painted parts of the boat. I varnish a lot of high-wear areas,
like the spars, the rubrails, and the companionway hatch, and they have needed only a a few touch-ups after two seasons.

[dbeck]

Thanks Doug. On the hand I assume we use the same product. At least the can, label and description look identical to the product available via the CLC home page. On the other hand it is strange that the technical data sheet describes how-to varnish wood or previously varnished wood but varnishing an epoxied surface is not mentioned.

In comparison with the paint, our experience is quite the opposite of yours. But we used two-part paint which is supposed to be more resistant.

Hm... I am not sure how to proceed when we'll start varnishing mast and spars in a few weeks. Switch to two-part PU varnish?

[[email protected]]

Possibly your epoxy leaves some amine blush, and you need to more aggressively clean it off before varnishing.

I have done a lot of printing on a couple of antique cars, and I have experienced the heartbreak
of seeing the finish coat peeling off of the primer. The culprit was usually using products of different brands.
It's even worse when it only starts happening after several months, after you have reassembled everything...

On my boat I used Interlux Brightsides. Even small scratches on the white deck, for example, are fairly conspicuous. I sort of wish I had used a 2-part paint
like Perfection, but when I was painting, nobody had it in stock.

[dbeck]

Maybe I was not clear enough. Our varnish is far from peeling off on its own. It makes a good overall impression. But it just sticks not as good to epoxy as we expected.

As an example, when painting the upper hull, we protected the previously varnished rubrails with tape made for masking. But when peeling the tape off, there are some spots where the varnish preferred sticking to the tape instead the epoxy. When using the same tape on surfaces with two-part paint, we never had an issue. On the one hand, the culprit might be the tape. On the other hand it seems the varnish is more sensitive to mechanical stress than the two-part paint.

I am thinking in three directions.

1. The pocketship manual says nothing about primer. But maybe we were supposed to use a clear primer developed for application onto epoxy and we missed that?

2. Maybe the International Schooner varnish is not intended for application on epoxy at all? Neither the instruction nor the description mention the application onto epoxy.

3. I am also not sure if the varnish sold in Europe is identical to the one sold in the US. The data sheets give different VOC values: 420 g/lt (US) and 386 g/lt (Europe). If the European version its chemically different, it might behave differently. Another difference is the epoxy. CLC favors MAS but our (European) kit from Fyneboats came with PEC.

For mast and spars,I am tempted to switch to one-part or two-part PU varnish from the same source where got our two-part paint. For those products, the data sheets explicitly mention application onto epoxy.

[Creekboater]

I had an issue with varnish over epoxy when building my spars. It wasn’t peeling off but just wouldn’t harden, remaining mildly tacky. Turns out part of it was my non-blushing epoxy was blushing and I never recognized it because I wasn’t expecting it. I also found that a little Japan Drier works wonders in helping stubborn varnish cure.

[slash2]

What epoxy did you use?

[dbeck]

I started this topic and like to sum up from my point of view.

We contacted the support of International. Very friendly and helpful. About primer, they provide no primer to be applied between epoxy and varnish. So we did not miss that . Although schooner seems to work well on epoxy, this is not intended use. Its intended for application onto wood. The first coats will penetrate into wood and adding more coats will build up a varnish with a very strong bond to the wood; but there is no penetration into epoxy. For a very strong bond with epoxy, one would need a two-part PU varnish, but International does no longer provide it to the end user (at least) in Europe. When sanding epoxy, I understood one should to do 120, 180 and 240 grid. Not in one step from 120 to 240 grid as we did.

We have contacted our 'local' store were we bought all the two-part paint and lots of other stuff. They recommend either some oil-based finish on plain wood or two-part PU varnish on epoxy.

What will we do?

All surfaces we varnished so far (transom, breast hook, companionway slide) will stay with Schooner. We'll sand the bad spots on the rubrails and 'repair' with a few coats of Schooner. I guess we'll have to recoat the rubrails once per year anyhow.

For mast and spars we'll order two-part PU varnish although we will not have the warm honey colored look as we have with the Schooner finish.

[slash2]

Weird. I think CLC has done countless boats with schooner over epoxy. That’s what they sell, so I’m sure it is has been used by many people. I asked which brand of epoxy as that could be the differentiator. Maybe MAS is more varnish ’friendly’. It is an amine blush-free epoxy so maybe it’s just ‘different’.
In any case , sorry to hear of your finishing troubles. That must be very frustrating to get to that stage and not have it go well. Good luck!

[dbeck]

Steve, our kit is from Fyneboats in the UK and is shipped with epoxy from PEC not MAS. But I don't think this plays a role as the technical support of International told me that Schooner and epoxy do not interact with each other chemically. I don't believe we had an issue with blush. The bad bond occurs mostly at the round edge along the rubrails where I did sand manually. Maybe I did not sand well enough. Whatever.