Sanding before hotcoat with RR Epoxy

In the archives (Epoxy and EPS Construction primer ) it is stated that no sanding is needed between the lamination and the hotcoat if you use Additive F


It also doesn’t interfere with recoating as wax solution in polyester does. That means no sanding between layers.

However this post;sb=post_latest_reply;so=ASC;forum_view=forum_view_collapsed;;page=unread#unread

says that


You need to sand off as much of the hotcoat as you can and lam on one more layer of glass, nice & dry, and then give it a fill coat within about 4 to 6 hours after it starts to harden…

which seems to imply that there is some sort of time period during which the bond is better.

Can someone clarify this because I will probably have to wait for RR Epoxy to come back in stock after I have laminated and before I can finish hotcoating and would like to know if I have to sand between layers if I have to wait to finish.



You can fill coat any time after it starts to set up, but its best to not weight over 24 hrs (you end up with a mechanical bond instead of a chemical one)

Take all claims regarding just about any epoxy product with a grain of salt.

“No blush” is perhaps more properly termed “minimal blush.” Also keep in mind that temperature and/or humidity parameters should be adhered to or all bets are off - even with surfacing agents. Cold temperatures and/or high humidity conditions may cause even “blush-free” epoxy to blush.

From the sound of things, you will definitely be beyond the recommended time limit for no-sand recoating.


Take all claims regarding just about any epoxy product with a grain of salt.

Agreed! Epoxy does have its quirks and it likes having things its way. You need to control your environment much more than you would with poly resin (its similar to not letting UV poly be exposed to uv until your ready)

Thank you both. Interesting that Epoxy went through a ‘it will solve all problems’ phase but now people are noticing things eg recent thread about possible reaction with PU blanks and mentioning the need to post cure to reach decent hardness.

I’ve only made a set of fins and done the fill/sealer coat on the EPS but happy to put on a lab coat and follow the rules because its a relief not to have the stink of styrene.

Im using a glassing room where UV polyester glassing usually goes on and have watched a couple of boards being glassed this way. Going to get the room up to a decent temperature and have got all my measuring stuff and chemicals ready on my own table to keep stuff clean. After the shaper/glasser I watched had laminated the bottom he sanded the laps in the same room and then carried on glassing the top. I have read in other posts that problems can occur with fish eyes on gloss coats due to dust particals. Am I likely to have similar problems with hotcoat /fillcoat given that I am only after a normal sanded finish? I can take the blank to the sanding bay and sand the laps but that necessitates taking out of the warm room .