I recently finished a second board using DHP epoxy resin over a standard Clark foam blank with S glass. Here are some observations.
First the good:
It’s amazingly strong stuff. I’ve dropped the first board on rocks, parking lots, etc. with zero damage. The area under my back foot has compressed slightly, but considering I weigh in at about 220 with full rubber, it hasn’t dented much at all.
The sanded finish I used for the first board had an odd, but cool “grippy” feeling to it. I ended up liking it because the unwaxed areas of the board weren’t at all slippery unless I was wearing gloves.
The odor—almost none. Very pleasant to work with. My wife could actually walk into the garage and not gag while I was laminating.
Quick working time. You could shape a board in the morning, glass it mid day, and surf it for a morning session the next day.
The not so good:
You’ve got to lap your rails as quickly as possible, due to the quick setting properties of the stuff. Kind of hard to explain…it gets thick almost immediately due to the temperature difference between the microwave oven and the surface of the blank. This is disconcerting, but not a big deal, as the resin is still in a workable state. The rails just need that extra bit of low viscosity to saturate and wrap before the resin cools.
It’s not unlike glassing with goopy snot. Not that bad, but DHP resin is stickier than anything I’ve worked with. It takes some getting used to.
You need a microwave to heat the epoxy, a cheap mixer to thoroughly mix the two parts, and an electronic scale to accurately measure the two parts. I never had a problem with mis-mixing the two parts, even with small batches. The surfacing agent, and the white and blue pigments were a pain in the ass to get out of the containers.
You need a hot box to cure it. I spent thirty bucks on rigid foam insulation panels, put them together with duct tape, put a meat thermometer in one end and a hair dryer in the other and viola! A hot box. Worked great.
The ugly:
It’s very resistant to sanding. For anyone with better laminating skills than I possess, just about all of you I imagine, this may not be an issue. For the first board I built with DHP, sanding was a minor annoyance. For the second board, and this is where things got ugly, sanding turned into a nightmare. After a flawless lam, I started in on the sand coat and was horrified to see thousands of little fisheyes appear in the resin. No matter the number of times I spread the resin out again, the fisheyes reappeared. In retrospect, I should have just skinned the coat off and started over but, well, it’s expensive stuff and I figured I could just sand it out. Ha! I must have spent 20 hours trying to sand that coat off, and it just never got back down to an acceptable smoothness. Admittedly, I was using an orbital sander, but with 40 grit paper. I didn’t have the grinder set up to do surfboards. I tried a small patch of System Three epoxy over the rear of the deck to see if it would adhere to the DHP. That worked fairly well, but it was yellow compared to the ultra clear DHP. Next, I tried some of Greg Loehr’s Resin Research West epoxy on the bottom to see if it would go on over the fisheyes…no luck. But it stuck, which Greg wasn’t sure was going to be the case. Finally, after setting the fin plug with RRW epoxy I dumped the excess on the deck to see what would happen, and it actually stayed over the fisheyes. I guess I just needed a thicker coat on the bottom. Mark at AST was perplexed about what would cause the fisheyes, but I have a feeling it was high humidity in a relatively cool environment that may have led to the problem. Ultimately my fault for not controlling the glassing environment better.
I was intrigued by the claims of low toxicity and strength, but for a low volume guy like myself, the technical requirements ( I mean skill and facility with the material ) were a downer. For a factory setup, with professionals, things would undoubtedly go much smoother.
Miscellaneous notes: I put in a set of Speed fins with DHP, with no fiberglass cut up to form a matrix, just the epoxy. A year later—no cracks, no problems.
I mixed the stuff at about 110 degrees F, hot enough to get rid of the bubbles, not so hot as to reduce the working time too much.
Heat your work area so that the blank is warm prior to glassing. A dehumidifier might be a good idea too.
That’s it. On to the next board.
