Tuna, thanks for the microwave tip, i'll have to stop by sometime... its just hard to commit to GA surf... I dont want to scare people out of epoxy, just be sure to follow directions. Also, allow yourself one "practice" board. But I'll def. be trying the microwave. Gotta pack... fluffy.
jong ....a large wooden box with a blowy heater ,somewhere between 60 and 80 celsius ...
I've glassed in 55¼ with no problem. What probably happened was when you finished glassing in 55¼ you then left the shop and the temperature then fell from there. All thermoset resins have temperature issues and ours certainly is no different. The simple way to eliminate these issues is to heat a work area. Keep things around 65 to 70 and everything will work great, this includes the curing time. And the boards come out better too. On the frothing, we had a choice we made a long time ago. As Bert said, some epoxies don't froth and we seriously worked on formulas that didn't. The problem we ran into was that those resins are not very reactive. This means to make the resin reasonable, speedwise, we had to increase the reativity of the hardener. This caused the system, overall, to be MUCH more toxic. The froth issue is simple todeal with using the techniques mentioned above. We didn't see the point in raising toxicity for such a minor issue.
RE the froth issue, you can use more resin and not have to spread it around as much and avoid the froth. But I'm looking to play to the strengths of epoxy and build the lightest strongest board possible. That requires pulling as much resin off the board as possible during laminating and getting the cloth to bond as tight and close to the blank as possible. So I have no complaints about a little froth if I get in a hurry. As besides, while I don't know how far I want to take this, air-entraned resin (ie froth) ought to be lighter per unit volume, albiet, marginally so.
Personally I'm always ready to learn, although I do not always like being taught. - Winston Churchill
Jong and GregT, have you thought about priming the blank with a microballoon slurry before laminating? Helps with glass/foam adhesion and allows you to sweegee off all excess resin and pull the cloth tighter onto the blank. An experienced hand will get close to vacuum weights. Although there have been critics of this technique in this forum in the past, it is an aeronautically accepted standard and highly recommended for saving weight, gaining strength and ensuring bonding.
Thanks Dale, interesting article. I guess my reference is to the part on filling the cells. Surfboard foam is actually very high quality and quite dense compared to some crap I've worked with, and filling is probably not actually necessary. I must say though, I achieved much better results by doing it, and would recommend it as an extra step in the direction of better quality, not only in strength and weight, but in a tighter reproduction of the original form. Not all shapers out there shape boards with allowance for the various laminate thicknesses, and I don't blame them. After all, it's only a surfboard.
Here are my hints for epoxy use
1. Resin pumps. They only cost a few dollars each and its in the interests of our health that we don't go dripping it anywhere
2. electronic weighing scales will allow successful measuring of smaller quantities of resin - useful for doing smaller jobs such as fin boxes. Accurately measuring small quantities of epoxy is one of the difficulites with working with this resin.
3. This one is for the neurotic board builder. Try and have a mixing system which avoids the following scenarios which i have gone through:
a) Stare at the rather similar looking 2 containers of epoxy and wonder if i really did mix up part A and B or whether i accidentally added two lots of A. Decide to throw away mixture and not risk wrecking project only to find it sets fine.
b) Stare at the rather similar looking 2 containers of epoxy.... same as above but decide to go ahead with lam anyway and then spend 1 hr worrying if it is going to set.
On the subject of mixing pumps, we used them for years. They are inaccurate and slow down production unless your buying REAL pumps. The professional kind for big bucks. Scales also work but most company's mix ratios are set up for volume mixing so the ratios are a bit difficult which can cause errors. Today there are metered buckets available at almost every hardware store and they are resonably accurate, much simpler to use and CHEAP. Since we switched to these we have NEVER had a bad batch in our shop. We've found that keeping the system simple keeps errors to a minimum and quality consistant. Over teching the work place isn't the best way to build quality.
As for sealing we generally use spakling compound. We've run tests comparing microballoons and epoxy with spackling compound for peel strength and, beleive it or not, the spakling compound was every bit as good or even better.