Time between coats of Epoxy and sanding finish questions?

Hi -- I'm still working my way through a Shearwater Sport.  

About 36 - 48 hrs ago I finished a second coat of MAS Epoxy on the deck to fil the weave of the glass.  Upon inspection today there are a couple spots where I can still see and feel a bit of glass weave, plus a couple wavy/low/high spots in the epoxy.

My instinct is to roll on one more layer of epoxy so that I don't sand thru -- however I"m concerned about how long it has been since the last coat of epoxy?  Will a third layer bond well to the previous two coats since it has been so many hours since?  

Or would I be better to lightly sand with 120 grit be careful not to sand thru and then recoat?  

Also any tips or useful tools to fair out those high/low spots on both the deck and hull? I'm often not sure how "flat/fair" it needs to be.  I read somewhere that after sanding, when I wipe with denatured alcohol that will indicate what the finish will look like with varnish -- Is that correct?


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RE: Time between coats of Epoxy and sanding finish questions?

36 - 48 hours should be enough time for a MAS epoxy coat to cure hard enough - IF your work area's withing their temperature recommendations - not to take a fingernail impression yet still be 'green' enough to bond well with another coat.

That fingernail test is good for determining when you can sand and not get gummy build-up on your paper. Do be cautious still about breathing the dust from sanding. It's not fully cured for some time yet (depending on which hardener you've used and the ambient temperature where you're working) and whatever unreacted hardener's present remains a serious irritant.

If the fingernail test shows it's hard enough to sand but you don't want to sand into 'glass cloth, try using brown or green ScotchBrite abrasive. It does a wonderful job of breaking a gloss surface without removing much material at all. Sandpaper's useful stuff yet I find the ScotchBrite tends to follow the minute texture of party-filled cloth better than sandpaper.

Yes an alcohol wipe does give you a good simulation if what another coat of epoxy will look like once cured. Be ever watchful for contamination when doing this though, it's too easy to bring something with that alcohol and your application media (paper towel, cloth, whatever else you have handy) that'll give you fits as you watch areas of that next coat bead up in spots before your eyes.

RE: Time between coats of Epoxy and sanding finish questions?

 I second the motion for a Scotchbrite rubdown before putting on another layer of epoxy. It's easy to do and won't dig into the bumps of the weave. You'll need to clean well, just as though you'd sanded. My routine, and the routine CLC recommends, is vacuum 2x and rub down with denatured alcohol 2x.

I've been using common hardware store denatured alcohol with no issues. My wipedown rags are all "virgin" - fresh out of the bag - so in theory they've never touched a contaminant. When done you'll want to give your craft a good eyeball for bits of lint.

Where can I get some of that party-filled cloth? Sounds just like what 2020 needs. :)


RE: Time between coats of Epoxy and sanding finish questions?

Thanks for the tips on the scotch brite pads -- that makes a lot of sense!  I'll start in on that and then clean throroughly and then apply another coat of epoxy.

I feel like I'm at the 90% done 90% to go phase -- everyone who comes by and looks at the boat is fairly impressed and asks when I'm putting it in the water.  I don't even have the coaming on yet -- and I have a lot of little finishing steps to do....

Thanks again for all the advice -- I'm very thankful for this forum.


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