Epoxy hotcoat sanding problems

RR epoxy with 2x Additive F; cured overnight in warm shed (about 70-73 F); cold outside 40 F by morning, shed was cool too as heat was turned off past mid-night. The glassing & sanding was done by a very experienced poly person. The resin was mixed for 5 min.

Rough sanding the hotcoat w/ 100 grit the epoxy sort of “swirled back into itself” and tiny pellets, not dust, came off the board. Sanding took about 3x longer than normal. A little gumming on the paper.

What could be the cause of this? We’d like to get it right.

Thanks

If you get little balls or pellets instead of dust when you sand, then the epoxy has not cured enough.

this is then way the old epoxies sanded, never have this problem with Greg’s new RR epoxy, let it cure longer. I usually wait a day or so before sanding, I spot patched over laminates and it seemed to be cured, but did the same thing when I tried to sand too soon

Thanks. It’s Resin Research stuff. I think we need the fast hardener and a warmer room. The stuff’s WOW factor is really high! Second board will be better.

Whats the best way to seal the blank for tinting: spackle it twice or the EPS dust + 3oz. epoxy method?

Also, what the best way to apply the spackle along the rails? Perhaps it was too thin?

If it is cool, the resin can take a long time to cure. My fin layups in San Francisco takes days to reach full stiffness. I’ve definitely learned that once the epoxy work is done, keeping it warm (>70F) helps a lot.

Slow at 70¼ takes awhile before you can sand. Use fast next time in the temperature range your working in this time of year. It does it’s thing in half the time.

Skip the spackle. You get a better bond just using a little extra resin. You also avoid any discoloration problems. I tried out both on some scrap EPS & then did brake & peel tests. The strongest is also the easiest - lam right onto the foam, no seal coat either. The spackle method might be lighter, and is a little cheaper, but the bond isn’t nearly as good. Not even close. Glass & resin peel right off spackle with hardly a touch. Glass & resin onto foam tear away 1/4" of foam when you try to peel them up.

I was asking about sealing the blank in order to prep it for tinting.

Greg says to spackle twice. I’d like to know if sealing with EPS dust & epoxy (the Phillips method) will acheive the same consistant smooth surface for later tint work.

Thanks,

You’re right, of course! (Memo to self: read ALL the words)

Still, your strongest bonds would be if you tinted your lam resin and went straight onto the foam with it…

For sure, lamming right to bare foam gives the best bond. Spackle the worst, but leaves a nice, smooth finish for art work. In between is the microbubbles with epoxy - twice gives you a nice finish, and a better bond than spackle. But it takes time for the extra steps, and some extra materials. Structurally, I like to use a good, tight foam (like Surfcore), so I really don’t need to seal with anything, or I’ll use just a thin film of micro/epoxy, with some white pigment (and I use the fast cure hardener).

I recently built two boards, spackled (once) and painted one, sealed the other with micro/epoxy and did some resin swirls. The paint-over-spackle, once lammed and hot coated, came out a perfectly even color. Aesthetically beautiful. Used regular acrylic house paint, too. Freelapped.

The micro/epoxy sealed board was resin tinted and cutlapped. When I lammed the deck I started to get bubbles under the lam from outgassing. Figured out it was (1) only where I razored the lap and cut through the seal coat and into the foam too deeply, and (2) lammed on a warming board… BIG mistake. Lam in a constant temp or falling temp (so the foam will suck instead of blow).