Epoxy Hotcoat Dilemma

Hello all,

I was wondering if anyone (Greg in particular since I’m using his resin but any help is greatly appreciated) can help me with an Epoxy question. Here is my situation. I have laminated a polyurethane blank (Clark or Walker, I can’t recall) with Resin Research epoxy and after digging through the rest of my laminating supplies I found that I some how had just enough resin left over for the hotcoat with no hardener in sight. How that happed is beyond me, my bad indeed, but that is not the point here. I found a source to order the hardener from but due to an in-house error on their part I just received the hardener over a week later than promised. So due to both of our oversights the laminated board has been sitting 10 days total with no hotcoat. The laminated blank has been completely covered with painter’s plastic the entire time while waiting for the hardener. I found this thread


in the archives and would like to avoid sanding the entire exposed weave lamination as I am always hesitant sanding weave with color work and using any type of solvent or water as a cleaning agent. I realize the hoatcoat should “wetout” the sanded laminated weave clear but I have had problems with epoxy leaving a “sparkle” to the sanded weave under the hotcoat that I have not had with polyester in the past.

Here are a few of my questions and any suggestions or advice is appreciated.

  1. Is sanding the entire lamination absolutely necessary and what would be a possible draw back of hotcoating to a straight un-sanded lamination?
  1. Has anyone here hot coated an un-sanded epoxy lamination that has sat more than a week and what were the results?
I know some people are going to respond that I should sand the lamination and wipe or clean the laminated board with denatured alcohol, vinegar, soapy water, straight water, etc… as outlined in the previous thread but all my experiences in the past have been unpleasant with leaving unwanted “sparkle” under the hotcoat and cloth fibers behind pre hotcoat. Like I mentioned above the board has been covered with painter’s plastic the entire time so cleaning shouldn’t bee an issue unless blowing the blank off with a compressor will not suffice.

Thank you in advance for any help.

The problem is that epoxy doesn’t like to bond to cured epoxy…

I have had a board cure over night, but in very humid conditions, and after sanding the hotcoat and pinlining it, the taped pulled up a couple of sections of hotcoat exposing the cured weave below it. That one was a case of a lot of blush, I think.

You could try it, but I don’t think you will get a good bond to the weave without sanding it first. Just scuff it up nice to give it something to bite into. If you don’t sand it too heavily, it shouldn’t mar your colored lam … I have done it before just to be sure to get a good bond… just a quick go over with a piece of 80 grit sandpaper.

…always done it within 24 hours though… YMMV

Oh yeah; don’t use vinegar to clean anything before coating with epoxy. It stops the epoxy reaction, so any residue of it will ruin your coat.

I’ve got a feeling that 80 is too harsh, correct me if I’m wrong…

Give it a rub with a green kitchen scourer, that’s worked for me…

just give her a light scuffing with 100 grt dust her off and go for it

Ive waited days before sand coat , no scuffing , no problems

no additive F in the lam , right?

harvest, if you don’t sand the hot will chip. i sand all my hot coats sligtly with 180 (you dont have to expose the weave) and clean it with water. i had bad experience with alcool. you might try it on a mirror and see what stays when it drys.




 I've got a board I started last August. I airbrushed it around September. Laminated it in November. Finally got around to hotcoating it in December. I still need to sand it down. 

If you blow the board off with your compressor you’re taking a chance of blowing out oil from your compressor. The only parts you should have to scuff down are shiny spots where you might of left too much resin while laminating. Sand down the laps also. The more you can sand down before the hotcoat will give you a cleaner finish after the hotcoat has been put on. and less sanding required afterwards.


Hello Harvest,

I was taught that in order to get a good chemical bond between the lam coat and the hot coat you must do all your steps within 24 hours. Any time longer than 24 hours you must sand the lam coat in order to get a good mechanical bond.

You will need to sand your lam coat before hot coating…

I stay away from solvents but many Swaylockers take that route…

My air compressor is oil free and it has a filter so I’ve not had any problems with using an air blower on my boards.

Hope it all works out


ps…all my eps/epoxy boards now get a second hot coat after machine sanding with 100 grit. Like a gloss coat with poly but I do a sanded finish.

Whatever grit you choose, make sure you do a denatured alcohol wipe with a CLEAN cloth. I keep a “box of rags” in the shop… those thick paper towel type things that you can get at Depot in the paint section. Use them once and throw them away. The wipe is critical. Do it with gloves on.

I use 80 grit… bigger scratches = better mechanical bond. You’re not trying to sand anything off. You’re just roughing up the surface. Make sure when you look at it under the lights you see no large areas that shine. The whole surface should be dulled with scratches.

Hello all,

Thanks for the assistance everyone, it is greatly appreciated.