Failed Hot Coats - Need Help

Hi, I have been shaping/glassing for a couple years and have had little to no issues with hot coats… until now. When applying the hotcoat it looked good briefly then little pinholes appeared everywhere that quickly became gaping holes all over the board. This was my first time working in a new space but my process was exactly the same and I have zero idea what went wrong. I tried to correct any errors before hot coating the other side of the board only to get the same terrible result.

We are using Resin Research Epoxy Resin, the room was at about 78 degrees (not ideal but should be hot enough), added a capful of additive F, resin/hardener ratio was correct, board was meticulously cleaned with denatured fuel, then dried, and not touched with bare hands for a bit before applying hotcoat. No airflow in the space blowing dust around as far as I can tell. I am at a complete loss as far as what went wrong and any possible ideas could be very helpful. I have added some photos of the result to try and better explain.

Looks like contamination to me. I’m not a big fan of cleaning products / alcohol for my epoxy builds. Maybe your product had some additives ?
I never use anything. I just do a light sanding of the lam (without touching the glas) I just wash my hands with soap before sanding and rub sanding dust on my hands every now and then. Never had any issues (only 60 boards till now)
Same routine for sanding my fillcoats before I gloss/finishcoat.

Interesting, this sounds like a good plan. My question is how do you get all of the dust from sanding off without cleaner? I think the ideal setup would be an air compressor but we do not have access to one.

I don’t like air compressor. To much risk of oil particles. I simple vac with a brush attachment. That attachment is always stored in a clean box and only used for coat preparation. After sanding, immediately before coating, I run a strip of tape over the board.
I use a standard industry epoxy, no additive F.
My coats always come out like this one:


Great work. In my only two boards I vaccumed the dust and then paper tower. The problem was that the sanding dust becames all over the vacuum cleaner, specially the engine, so I did one of this:

Good luck

is that EPS or PU? Rising or falling temp in room? Only that area or the entire side? Did you mix epoxy any differently?

PU, whole side, falling temp

The only thing I use on an epoxy glass job is Dawn dishwashing liquid and water. No solvents. By the way, you mentioned using Denatured. It is very possible that the denatured broke down whatever you used for a rag and that became the contaminant. For example a petroleum based cloth combined with solvent could have created a contaminant. I notice a bit of a nose to tail effect in your contamination which tells me this may be what happened.


That looks like the dreaded silicone contamination.

I’ve built and repaired a few snapped XPS core boards and glassed them with Epoxy. I’ve also built wood strip canoes glassed and hot coated with epoxy.

On one of the boards I tried to repair the hot coat came out looking like your board. This was almost certainly contamination with silicone (the owner has previously mentioned something about putting car wax on the bottom of his board). Silicone is in everything these days. It spreads like crazy and is very difficult, if not impossible to get rid of.

Silicone is everywhere since it’s used in mold release agents for most plastic products. It’s in almost every car interior product and in fabrics, spray oils, waxes, paints, rubber like materials (your face mask and even some gloves) and in a lot of other products.

In my case, I had used the brush nozzle on my vacuum cleaner to vacuum the interior of my car that the previous owner had shined everywhere with vinyl shine. I later used this same brush to vacuum the dust from feathering the laps on this board before hot coat. I cleaned the board as usual using red ethanol (containing Ethanol >75 %, Propan-2-ol 10 %, Aceton <1 %, Butanon <1 % ) before hot coating. In this case the hot coat would scatter just like you are showing and it was impossible to get it to stick to the “dry” areas even though I tried to re-sand and apply more. I ended up just giving the board a ruff sanding and then giving it back no charge. I was told it surfed well and was strong but it didn’t look good at all.

I’ve heard other people who have had problems with alcohol based solvents and epoxy but I suspect that the problem is actually silicone. Be mindful of anything that could contain silicone and don’t store such items in the same room (or house if possible) as you are working with resins or paints.

There are expensive and dangerous solvents that can help to get rid of silicone. I think a thorough wet sanding under a lot of continuously running water, spraying with dish washing detergent or some simple green as you go along might work too.

I would avoid blowing your board with compressed air as well. There can be silicone or oils inside the hose or tank. Someone might have used some spray lubricant on a corroded connection at some point. I’ve even heard of trim carpenters who drip oil in the hose to lubricate the brad gun. You have to be a bit paranoid when it comes to this stuff. Let us know what you are doing with the board and how it turns out.

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Great info! Thanks! :+1:t4::+1:t4::+1:t4::+1:t4::+1:t4:

There is a video online somewhere of Jimmy Lewis showing how he takes a tiny amount of resin and adds an equal amount of filler (micro balloons) then forces that mix into the lamination to fill any pinholes. After that he lays down the fill coat. Jimmy Lewis also uses masking tape as the last cleaner on the board for the tiny dust. Look up Jimmy Lewis surfboards for the videos.

I laminate one side, then after about an hour add the fill coat. I do this before I touch the board, I do not flip it and cut the lap, I do the fill first. If I want to cut the lap, I do it with the board upside down on my glassing stand. It’s not easy, but I don’t touch the board until the fill coat is hardened. If I am filling the first side I laminate, I’ll try not to add resin where the other side will overlap. Once the first side is done, I lightly sand the rails where the lap will be. Then I wipe that area with Denatured Alcohol and repeat the laminating and filling.
I made a glassing stand with a bedside table that can be raised or lowered. I start with the rack low, then I can raise it up high to do the rail laps. The stand has a frame that I lay plastic over to catch spilled resin. I have an 8’ long frame and a 10’+ frame for longer boards.
A guy I know that used to make Epoxy resin boards back in the 80s told me he used to use Dawn soap and scrub the board after laminating to get rid of blush, but Epoxy resins are much better these days.
FYI… I’ve had issues like that on more than a couple of boards, and it seems like it was contamination. I used to glass in areas that could get a bit of air blowing and that will add dust. I also used to reuse mixing containers and not be concerned about contamination. I do all my glassing inside a more controlled room now, not like a professional room, but the best I can do as a hack making less than a handful of boards a year.