Epoxy resin issues - please help!

[kombatwombat]

Hi all, I’ve run into an issue and am a bit out of my depth.

 

I’m using a clear epoxy resin (Protite Casting Resin + catalyst) to create a clear glass effect on some terrain. I’ve used it 3 times previously without issue, but this time after curing there is a semi-opaque film on the top. It looks a lot like fog on clear glass.

 

The day I cast it was fine in terms of weather, though overnight as it was curing there was a spike in humidity. A bit of googling suggested it could be amine blush, and a proposed solution was to scrub it with warm soapy water and a scotchbrite pad (dish sponge/scourer).

 

As soon as it gets wet, it goes crystal clear. When it dries - either air-drying or with a paper towel - it goes foggy again. Scrubbing with the scotchbrite pad seems to make no difference to this beyond producing a few fine scratches.

 

Any guidance would be greatly appreciated. I already have a very expensive model incorporated into the terrain so starting again isn’t an option. Can I just add another thin layer of epoxy resin or will the foggy layer then just be trapped inside?

[Jalgar]

It was very likely humidity that caused it. Sometimes you can use wet rags to “wet” it out. Wiping the wet rags on epoxy will sometimes cause the fogginess to clear out. It takes a bit of patience though.

 

How long has the epoxy been set? If it has not sat and cured for days a light coat of epoxy will clear it out as well.

 

My wife does epoxied tumblers so I have helped her when issues arise.

[Semper Fortis]

Humidity will do it, but so will epoxy that is past it's shelf life. Usually it's only good for a year and then only if it's stored under controlled temperature conditions as with inside a home.

 

As Jalgar indicated, another thin coat will clear it. If it was a humidity problem then you are good to go. But if it was old stock then you'll just get another foggy layer. I have rescued a foggy old stock problem by purchasing fresh epoxy and pouring a thin layer of that over the fog. It didn't always work but it's surely worth a try.

 

Good luck and let us know how it turns out.

 

Edited to add: Just remembered another problem I ran into once. Failure to measure each part accurately can give sometimes give the same result, especially if you've added too much catalyst.

[kombatwombat]

Thanks for the help guys. The resin is fairly new and kept inside, it seems to be in good nick.

 

It’s been cured for about two weeks now, is it too late to rescue by pouring a thin layer over top? Otherwise I’ll have to sand it I guess, do you know if the whole piece will be clear all the way through after sanding that thin layer off and pouring another thin layer on top?

[Semper Fortis]

Kombatwombat, (love your handle btw) I don't know if it'll work after two weeks. I would be shocked if it's foggy all the way through. Remember the water on the surface cleared it right up.

 

Which solution you try depends on any deadline pressure you might have. Keep in mind that another thin coat will have to fully cure before you can sand it.

 

With no time pressure I'd give the thin coat a try first as it's the easiest solution. You just want a skim coat perhaps as thick as a sheet of paper for a small area. You'll likely have to go a bit thicker to get a larger area to level out and cover the entire surface. Basically you're doing the same thing as you did with the thin coat of water.

 

If that doesn't work then grab the sandpaper. I would start with a fairly aggressive grit first to get you through a few layers. Then work up to a nice fine grit. Make you you dust the heck out of it. An (empty) airbrush works well or a can of compressed air for cleaning electronics. Oh and don't breathe the dust while you're sanding and dusting. A paper mask will work fine but I can't imagine epoxy dust being good for your lungs.

 

Again, good luck.

[kombatwombat]

If that doesn't work then grab the sandpaper. I would start with a fairly aggressive grit first to get you through a few layers. Then work up to a nice fine grit. Make you you dust the heck out of it. An (empty) airbrush works well or a can of compressed air for cleaning electronics. Oh and don't breathe the dust while you're sanding and dusting. A paper mask will work fine but I can't imagine epoxy dust being good for your lungs.

 

Again, good luck.

Thanks Semper. When you say fine grit, how fine? The big thing I’m worried about is sanding it, then pouring a new top coat and trapping a ‘frosted’ layer in the middle due where I’ve sanded it. I’m looking at 600 grit and working my way up to 1200 - is that fine enough?

[Semper Fortis]

The only abrasives I've used on clear epoxy were to polish out a scratch or two. I don't know if 600 grit will take off enough stock to make a difference. I'd probably start with that in a small area, perhaps an edge, and work up to your finest grit. If you start sweating and cursing under your breath then you may have begun with too fine a grit. I'd probably start with 360 or even 320 but not lean into it too hard.

 

As far as your highest grit goes, 1200 may not be fine enough. Essentially you'll want to polish the surface. It's been far too many years for me to remember what I used to clear those tiny scratches. Just keep working until it's shiny. :lol:

 

Today, rather than sanding, I'd grab an abrasive in suspension. Novus Scratch Remover is what i happen to have handy. It's a set of three bottles designed to polish plexiglass and the like. The grit is suspended in a thin paste much like liquid wax and applied with a cloth. One advantage is that you're capturing all the dust in suspension and in the cloth thereby saving your lungs. Also the suspension acts as a lubricant so much less effort is required. I think I paid 9USD for it last fall. I used it on a sheet of Lexan and it worked a charm.

 

Hope that helps some.

[kombatwombat]

Thanks to all for your help! I managed to get it to work, and it’s come up crystal clear.

 

For anyone facing the same issue in future, the fix was to dry sand it with 400/600/800/1200 grit sandpaper, wipe off the residue with a damp paper towel, dry it out then pour a new thin layer of the epoxy resin on top (this time waiting for a day with low humidity). One trick was to sand in one direction with the 400 grit, then sand in the perpendicular direction with the 600, then rotated 45 degrees for the 800, then perpendicular for the 1200. That way you could see what grit size any scratches were. Came up beautifully.