Epoxy finish question, how smooth before polyurethane

[Graniterich]

I have put three coats of aeromarine epoxy on my walls. 98% is like glass, the other 2% is sealed, but has brush marks ( like that coat not quite enough, or I brushed at very end of pot time?). I want to go woodie, and I know it is now sealed, but after a lite sanding and three to more coats of semi gloss polyurethane do you think the 2% will still show? Don't' want radically sand all of it!

[Graniterich]

Pictures

[nevadatear]

You want it as smooth as possible before your finish coat, which should be a marine grade spar varnish, to truely protect your epixy. If your epoxy is not smooth, your final finsh will only highlight these imperfections, not hide. My epoxy was supersmooth, but i still had problems getting a smooth finish coat. Like anything else, your final product is only as good as your preparation and undercoats.

[Graniterich]

So I should mix another batch and just apply in the void areas, and pray for self leveling?

[tonyj]

Before adding the extra coat(s), use a cabinet scraper to smooth the runs or uneven surface. Do this before sanding. Those uneven areas might flatten out just fine. If not, add more in those areas, let it harden, then scrape, sand and feather in. I have found that three coats of epoxy is usually mre than enough protection before coating with spar varnish or poly. I prefer spar varnish for its added UV protection.

Don't be afraid to scrape and sand that shiny smooth epoxy surface. When you sand the final epoxy coat with 120-150 grit, it produces a dull matte surface that creates the mechanical bond between the epoxy and varnish (or poly). When you apply the finish to the matte surface, it becomes clear again showing all that beautiful grain beneath.

I use both flat card type cabinet scrapers and carbide scrapers before doing any sanding. Just be careful to not gouge the surface, or you will be adding more epoxy to repair those marks. Good luck.

[aggie79]

As others have said, whatever level of finish you have on your epoxy will transfer through to any top coat materials.

On my tongue box, the exterior cedar was tinted with TransTint dyes, followed by 3 coats of Raka expoxy, and the 3 coats of Emtech EM9300 urethane finish from Target Coatings. (I shot the Emtech EM9300 with a cheap HVLP spray gun made by Wagner.)



Because I had the time, I sanded between the epoxy coats. Even with sanding, as you can see in the above picture, the epoxy surface was not glass smooth and these imperfections can be seen through the urethane top coats.

[Graniterich]

Thanks for all your help! I think I need to go back and touch up those areas, don't want to do a whole coat, is that feasible? I think it was a case of lots of brush strokes, not a lot of time.

[nevadatear]

Most likely that will not smooth it out. Scraping and sanding are really the way to go here. Bring down the high areas. It doesn't matter if the epoxy is not shiny. The finish coat will shiny it up again. Fear not the sanding.

[MtnDon]

Polyurethane is like the clear coat on todays automotive finishes. It makes whatever is underneath shiny. If the underneath stuff includes bumps you end up with shiny bumps. Polyurethane aand plain old spar varnish for that matter, are not body fillers, are not meant to hide imperfections.

[Graniterich]

Ok, so I am going to build those areas up, and then sand even, thanks again

[doug hodder]

I'm sure others may not agree with me on this, but it appears to me that you have some sort of contamination on that upper edge just below the cut. The epoxy looks like it fisheyed to me. May take some time to get it squared away. Doug