Scratches in epoxy, under varnish

Doing bright finishing and have done the cloth, filled the weave, sanded smooth and in putting on the first coat of varnish I'm seeing some scratches in the epoxy that I thought would easily fill out with the varnish. I had sanded with 220 grit and the sanding marks weren't bad at all, I have overcoated sanded epoxy and scratches that were a lot worse have always filled in and disappeared. In this case they didn't.

I used Schooner Gold varnish (I know it's as thick as goo, but I thinned 2 parts varnish to 1 part brushing liquid, 33%, but it was still pretty thick). I also wiped the surface with the "brushing liquid" prior to applying the varnish. Wiping with a normal thinner would have dried easily, but the "brushing liquid" didn't dry really dry by the time I was applying the varnish.

Did the brushing liquid get into the scratches and not let the varnish get in there? That's my thought, I'm having a hard time thinking that the cutting from 220 grit isn't filling with the varnish.

Any thoughts?

 

I should also mention that the sanding marks are only visible in the "halo" of a light, not in the normal viewing of the panels. I am just thinking that it will be visible in the sunlight if the light hits it right.

Am I being to picky????

I did strip off a small area and it was easy to use aircraft stripper to clean back to the epoxy, then I cleaned it with water and then scrubbed it with lacquer thinner, let it dry and then put on a coat of the same varnish thinned 50/50 to see if a thinner mix will fill the scratches. Since I only have two coats on at this point it might be worth using a chem stripper and taking it back off and starting all over.

 

It's probably the brushing liquid in the scratches. Strip it if you're willing. Also, varnish takes quite a few coats to fill even light scratches. You should be thinking about seven or eight coats.

 

You might send some pictures, but the problem is one I have encountered where the scratches ore on the wood, not the epoxy.

I dont know the mechanism that creates them, maybe their shape that prevents wetout by the epoxy, but if your varnish doesnt fill them, they may be deeper.

 

Well now that the varnish is down, your choices are limited, but viscosity was the right idea.

Brushing liquids (Penatrol, Interlux 333, etc.) should be mixed with the varnish, not used as a separate agent. From experience Interlux 333 is just really good mineral spirits with some light oil and doesn't work as well as Penatrol. This said, Penatrol can affect the gloss if you use too much.

Strip it back and start again. Go over the surface with 220, then with 240, but I wouldn't go much higher as you get into polishing, instead of toothing. Roll on the varnish, across the grain, then brush it off with the grain. This should be done immediately after it's rolled, so a two man job does it best, one unskilled rolling, the other knocking it down with the grain. Don't over brush it, just move it along to remove stipple from the roller and let it flow out to self level.

Varnish is a feel thing, more so then applying a coating. It should flow uniformly and level itself out. Just a few strokes are all that's needed, in any area. Using a roller insures the varnish goes down in a uniform thickness and is far superior to a brush in this regard. Lastly, roll and brush SLOWLY, so you don't fling anything around and create more bubbles than necessary. You're not painting, you're just letting a brush softly separate the wet stuff, much like a notched trowel, so there's some place for the varnish to level into.

 

I'll try to get some pictures tonight, but I doubt it will photograph at all. We're talking about very fine sanding marks from a random sander and they are clearly in the surface of the epoxy, not in the wood. The wood was sanded, then stained, and any sanding marks in the wood show as dark scratches (there are a very few, I'm not perfect), so there really isn't any chance it is in the wood, and there is enough varnish on there so that they are not in the surface, they're definitely between layers.

In the halo of a light bulb they look almost like the marks that are left in the surface if you do a polishing job on a clearcoat and haven't finished with the finest compound yet. It's very fine and obviously between the layers, and as I said, you have to have the light just right to see them at all. My concern was that in the sunlight they would be visible, and I'll find that out this afternoon also and then decide what to do, and compare it with a test area I redid last night.

In doing the transom I did a cleaning with a good lacquer thinner, and then used a thinned varnish and all the sanding marks disappeared and I got a nice finish. This time I used the 333 liquid as a wipe down first, because that is what it said to do on the varnish can. That's what I get for reading the directions.

Par, thanks for the technique advice, helpful as always, I'll give it a try when I redo it.

I was doing the topsides first and had some sanding to do on the bottom and was then going to do that. I did get more dust in the finish than I would have liked, so I am going to flip the boat, and get every bit of sanding done, everywhere on the boat, clean the entire garage and get rid of all the dust, and then wet the floor when I'm varnishing. Don't expect it to be perfect, but I have too much dust in the air and the flat surfaces are seeing it. The sides look perfect, so it's just dust settling on the surface that is the issue here.

One last thing that I had thought of was to perhaps strip the varnish and then mix up a small batch of epoxy and squeegee on a very, very, very thin layer of epoxy, just enough to fill any scratches, and then just clean it with scotchbright and water to get rid of any potential blush and roughen the surface enough for the varnish to stick. Par, any thoughts on that approach???

 

After any machine sanding, always follow with a wet or dry hand sand, following the grain to remove any machine swirls.

You can try a very thin goo coat. I do this in prep of a finish, though you'll still have some hand sanding to remove squeegee tracks. Some times, I'll scrape these off when well cured (several days) then a final wet sand with the grain. Under clear coats, I try to hand wet sand last.

 

Par, Thanks, Lesson learned. I was wondering how to best strip the varnish. I used some heavy duty (Aircraft brand) stripper in an area that is going to be painted and it exposed some cloth, it was really aggressive. After it exposed a bit of weave in one small area that is going to be painted anyway, I couldn't make it disappear with application of thinner, like you can if you sand into some weave. If that were to happen on the area that I will be bright finishing, it would be a disaster.

Is there a stripper that can be safely used on varnish that won't attack the epoxy? I bought some "ready strip", which is described as a "safer stripper" and was thinking about using that, but I'm not about to do anything stupid now after seeing how the epoxy can be attacked by an aggressive stripper.

I took the boat out into the sun and really, you can't see the marks in natural light. If I can't strip the varnish off without eating into the epoxy I'll just let it go, but I'd rather do it right at this point. I think that if I can get it off I'll do the thin coat of goo and go from there with a hand sanding and that will be fine.

 

On the can of stripper, you'll see the terms "safe for fiberglass" which is the stuff to use. Second, don't let is sit on the surface too long. You can always apply more.

 

Strip it back and start again.....that is the only way now.

 

ordinary paint stripping chemicals will not remove epoxy
Paul Oman - MS. MBA
A.K.A. “Professor E. Poxy”
www.epoxyfacts.com
epoxies since 1994
Member: NACE (National Assoc. of Corrosion Engineers) -- SSPC (Soc. of Protective Coatings)

 

The normal "Aircraft" brand stripper by KleenStrip that I got at Pep Boys, is what really did a number on epoxy. It is nasty stuff. Thank goodness I tried it first on a place where I wasn't going to bright finish or I'd have been in deep do-do. They also have a version that is supposed not to damage fiberglass, but that isn't what I had. I also thought (mistakenly for sure) that pretty much nothing attacks epoxy.

I had to strip a deck today, not on the boat, the one behind my house so I didn't get anything done on the boat. I did have my son pick up some varnish remover that is "fiberglass safe" and will use that early next week and start again.

Thank goodness for MSDS. At least with that I can see what I'm getting. The stuff I am going to try is mostly methanol, butanone, and MEK, none of which it think will mess up epoxy, so this sounds pretty safe to use to me.