Hi, how hard does your epoxy cure? I have one layer of 6oz glass over the foam and it seems very flexible. If I apply pressure I can feel it flex. It has only cured for 24 hours, but I’d expect it to be harder still. I also have some test patches I did about a week ago that also feel about the same. I had the impression when I tested this stuff earlier that it did go off very hard even in thin layers. The gluelines on the foam was certainly vey hard. What is going on? regards, Håvard
Harvard, I built skimboards out of 2lb density per cubic meter eps foam and I used 3+2 6oz layers. After hotcoat and glossing, I left it cure for 3 days, then I tried to put pressure on it, I just felt its much stiffner than polyboard. I never dare to apply same strength on poly board, it’ll dent easily. Since most poly boards are light glass laminated, eg. 2+1 lamination. Previously Noodles did a detail explanation about the spring back strength of eps foam board glassed with epoxy resin, search the archieves you may have the idea of it. There are lots of epoxy resin of different usage, some for adhesive purpose, some for lamination, some for mold making and even the gloss finish of wood floor is epoxy resin. Mold making and gloss wood floor epoxy resin are more brittle than adhesive/lamination resin. I use high viscosity adhesive epoxy resin (short pot life) for glassing, it sticks well. I use low viscosity epoxy resin (long pot life) for hotcoating, I find it much easy to sand than high viscosity epoxy resin. Does the viscosity affect the strength/adhesive? May someone here can help. Regards, Crabie>>> Hi,>>> how hard does your epoxy cure? I have one layer of 6oz glass over the foam > and it seems very flexible. If I apply pressure I can feel it flex. It has > only cured for 24 hours, but I’d expect it to be harder still. I also have > some test patches I did about a week ago that also feel about the same.>>> I had the impression when I tested this stuff earlier that it did go off > very hard even in thin layers. The gluelines on the foam was certainly vey > hard. What is going on?>>> regards,>>> Håvard
I have run into the same problem. Although I have not done a bunch of epoxy boards the few I have done have come out with mixed results. I did an egg back in Feb. that came out very stiff and strong. I did a fish a while back with the same type (brand and weight) of cloth, same brand of resin and hardner (with same ratio), same type of sanding layer (epoxy resin), and same sanding job. The only difference between the two was the temperature during lamination. It was cold here in Feb and I was glassing at night (48 degrees). It was much warmer when I did my fish, (80 degrees). I don’t know if this had anything to do with it or not. You would think that if it kicked hotter it would be stronger (within reason of course). It was certainly easier to work with. I dunno what to think. Maybe you and I got some old hardner. I just did some ding repair on my fish and I used some older resin and hardner I had. After 18 hrs. it was still like rubber cement. I did notice that the hardner had a yellow tint to it. When I mixed it, the batch turned clear. Now that I think of it I remember the hardner being clear like water on my successful mixes. Maybe old hardner is our problem?
Håvard, You may have used temperaure degraded resin. You may have mixed in slightly wrong ratios. It’s easy to do if the epoxy resin is viscous. The resin mounds in your measuring contain, and doesn’t pour well into your pot. When you measure hardener in the same container, the container already contains an ounce or two of resin. That will throw your mix ratio off. Regardless of other problems… By covering EPS foam with one layer of 6 oz glass you are asking the EPs foam to provide the board’s needed strength. It won’t. EPS foam is weak and springy. That’s why, with little glass strength, you have a weak springy surface. I/ve written about this many times on Swaylock’s. You can get away with one - 6 oz layer over denser polyurethane foam (for a while) because poly foam is stiff and strong. Sorry you screwed up. Cut your losses. Sand the surface of your glass and laminate one or two more layers of glass over it. Next time laminate all two or three layers of glass together. A monolithic lam is stronger.
Hey Mike, I heat the high viscosity adhesive epoxy resin and make it flow better for lamination, may be here the temp is quite mild around 25-30 degree C. Therefore i dont have yours problems. Just learn from the web, as every 10 degree c temp increase, it double the cure rate. I just need 3 hours to turn the lamination into solid stage. You may build a rectangle box which capable to fit your board with 1 ft long in both end. Stick aluminium paper inside and place a 200w bulbs to raise the temp. inside, it may help you to speed up the cure rate and make the lamination more strength. Regards, Crabie
Hi,>>> how hard does your epoxy cure? I have one layer of 6oz glass over the foam > and it seems very flexible. If I apply pressure I can feel it flex. It has > only cured for 24 hours, but I’d expect it to be harder still. I also have > some test patches I did about a week ago that also feel about the same.>>> I had the impression when I tested this stuff earlier that it did go off > very hard even in thin layers. The gluelines on the foam was certainly vey > hard. What is going on? > > regards,>>> Håvard Hej Håvard Maybe You’ve mixed it in wrong ratio, epoxy is very sensitive to this. Also the ratio is different depending on if You measure by weight or volume. Could also be that the shelf life (best before date) on Your resin is overdue, or maybe curing temperature was too low. Maybe try postcuring it at a higher temp (40-60 celsius) it could maybe help. Be careful curing very hot, you could end up with altered rocker curve as the epoxy turns softish and bendable at high temps. p.s I’m not an expert only done one sailboard in epoxy long ago. Best of luck Erik
Thanks for all the info. I can think of a few reasons I didn’t get all that hard. I might have gotten a slightly wrong mix rate. I messured with a digital weight, but I poured the components in two different containers. I might not have gotten all of the hardener out of the cup when mixing it. I’ve noticed that when I use color in the epoxy it has hardened a little softer then clear epoxy. Dunno why. I sent an email to the distributhor of the epoxy here in Norway asking alot of questions. They noted that high humidity might cause the epoxy to cure slower and take up to a week(!!) to get hard. The epoxy would also continue to cure for about a month. It’s been pretty warm and way high humidity here for the last couple of weeks. I’ve added another layer, I was going to anyway. It’s much harder now, but I’m not sure I’m happy with it. I also noticed that the leftover in the cup was much harder than the previous layer. This time I messured the two components in the same cup and the resin was clear. If it doesn’t get as hard as I’d like I think I will add another layer of cloth on the bottom. Thanks for all the suggestions. regards, Håvard
Maybe you and I got some old hardner. I just did some ding repair on my > fish and I used some older resin and hardner I had. After 18 hrs. it was > still like rubber cement. I did notice that the hardner had a yellow tint > to it. When I mixed it, the batch turned clear. Now that I think of it I > remember the hardner being clear like water on my successful mixes. Maybe > old hardner is our problem? The hardener was a bit yellow out of the box, but I don’t suspect that’s the problem since my first test with it was OK. The distributor noted that it should have a shelf-life of 5 years as long as it’s stored properly(out of sunlight among other things). regards, Håvard