I’m going to shape and glass 3 small-wave shortboards using Surfblanks poly foam and Resin Research CE epoxy resin and I have a few questions:
I'm wondering what weight (6oz/4oz) and how much glass (layers) to use? My original plan was 6/4 deck and 6 bottom, but now I think it would simplify my life (and materials order) to use all one weight of glass. Two of the boards are for friends and I'm going to keep one. Do you save enough weight using epoxy to justify more glass?
An experienced shaper told me to seal the stringer of the blank prior to laminating so the stringer doesn't blow gas. The blanks I'm using have 3 ply plywood stringers. I've used the blanks w/ PE resin and didn't have to seal the stringer. Any thoughts?
What additive (thickener - Cab o Sil/Microspheres) do you add to epoxy resin to make a paste for sealing (the stringer)? I plan to buy Cab o Sil for setting the fin boxes.
I plan to use epoxy b/c I can use it in my garage w/out stinking up the neighborhood and I want to get familiar w/ how it works b/c I plan to do some Timberflex boards.
Any other suggestions or words of inspiration are welcome
I have made several boards using RR over PU blanks and never sealed the stringer and have had no problems but maybe I have been lucky so I am interested in hearing from others if this has been an issue. As far as weight goes I don’t think you get a substantial weight advantage using epoxy vs poly resin on the PU core, maybe some if you are fruitful with resin, but I like to believe there is an advantage for strength. I think you can easily get away with one weight of glass… last board I made was a 4/4 deck and 4 bottom on a grom board and had very postitive results. Other option for addtional strength would be S-glass but that certaily adds cost.
Use whatever glass schedule you’d use for PU/PE. There’s no significant weight advantage using epoxy, unless you do it over EPS. The weight difference between EPS and PU is what justifies a heavier glass bill.
I wouldn’t bother sealing the stringer. I’ve used plywood stringers before and had not outgassing problems from them. I have had outgassing from cheap EPS, though. But never PU, with or without plywood sringers.
I use microspheres with epoxy for sealing. It’s lighter, sands easier, and stays where you put it. Never use cab-o for sealing. Only for filler that requires strength.
All I do is epoxy over poly. Resin weight is negligible. You use less resin with epoxy, but not enough to notice in the weight of the board. As mentioned above, the big weight difference is in the EPS vs Poly blanks.
I do not seal stringers and have never had a delam, but I have had foam expansion along the stringer with certain foams.
My standard RR CE glass schedule is 6/4 deck and 4 bottom. Epoxy is more flexible than poly. However, it's flexural characteristics are also what give it it's strength advantage. Epoxy glassed poly will pressure dent easier than poly glassed poly and epoxy glassed EPS due to the flex of epoxy, but in my opinion that flex makes for a more lively board that maintains it's flex longer. It will feel softer to the finger squeeze test. If you want to avoid the pressure dents do 6/4 deck and 6 bottom or 6/4 deck and 4/4 bottom. For my preferences a 6/4 deck is minimum for poly/epoxy combo to reduce pressure denting. S-glass is a very good option for durability.
A few more hints for first time epoxy use. Use at least 5oz more resin for the lam than what Greg recommends in the epoxy manual. Nuke the resin for 10 seconds then add hardener and F. Pour it all out on the board and push it around so that ALL the cloth is covered and the epoxy is soaking in. (do not leave resin in the cup, it will get hotter that you think possible) Then hold the laps and paint the laps with your squeegee until they are also 100% covered with resin. Then tuck your laps. Then pull all the excess resin off the board with the squeegee. While pulling the resin off look for air bubble and spots that didn't fully wet out and use the excess resin to soak these areas. You may need to push the resin into these spots. Pull resin off until there are no shiney puddles. Epoxy doesn't kick the way poly does. You can still work it into the bubbles even when it's gelling so don't get too nervous. As long as you spread it out good initially you should be ok. When it's dry, sand down the high the high spots on the laps, nose, and tail (not the weave, just the drips and hardened frayed cloth). This will make your hotcoat go much smoother. The hotcoat is pretty much the same as poly. Get it all spread out quickly first. Then pull it down the rails. Then if you get any spots where the resin pulls away leaving exposed weave, use your gloved finger to rub some resin into that spot. Then pull the excess resin off with the brush.
I’ve never had to seal polyurethane blanks when I’ve glassed them with epoxy. Never. If you really feel you have to seal the blank for god sake do not seal the stringer! I would recommend you use the same glassing schedule as you would feel comfortable with when glassing with polyester. The board should come out lighter and stronger when using epoxy as well. Just don’t treat the resin like polyester.
If you’re unfamiliar with how much resin to use try half of what you would use with polyester. You’ll probably have too much epoxy left over but better too much than too little. Don’t be afraid to mix another batch of resin if you’re first one runs out either. The only difference will be a few minutes in curing time between the two batches. Unless you rush mixing the second batch (if needed) then you risk mixing it wrong.
Use Add F as well. The mix ratio I use is 1ml of Add F per 100 grams of epoxy for laminating. That’s resin not hardener. Double that for fill coating. You can probably guess from that I measure epoxy by weight and Add F by volume. Add F will make your life just a wee bit easier when it comes to sanding and getting the fill coat to bond.
I agree on the sealing, I've never had to it with urethane other than Walker.
You do get a significant weight savings using epoxy which makes a more lively board. With the glass schedule your using you can count on getting the board in under 6 lbs. and still be pretty tough. It'll come out about the same as a 4 double 4 with poly.
How does the XF hardener hold up with the Blue resin? Does it still discolor as quickly? The fast is great stuff, but I was wondering if the Blue would give the XF more color stability.
