I know the guys here who use epoxy glass their board heavy, atleast 2x6oz bottom, 3x6oz top. Is beacuse of the properties of the epoxy or is it just because of the EPS being softer then PU clark foam? If using an EPS with the same compression strength as regular surfboard PU foam, could you use as little glass as on a PU foam? I would think that the shear(sp?) strength would have to be close as well. My guess is that a EPS blank with the compression strength of PU would be alot lighter, but lack of shear strength could break the board. While we’re at it, what is the specs for the different stock clark foam blanks? I cannot find any specs for density nor compression or shear strength. regards, Håvard
Everyone I know only uses a double top and single bottom (with no problems), but we are all using 6oz. instead of 4oz. If you used epoxy resin on a poly blank, you are going to obviously net a much stronger board but you won’t benefit from the light weight and added float of an EPS blank. I have not been able to find a cost effective alternative to 2lb. eps bead foam in my area. You might have better luck over there. I know Peter uses some pretty dense construction foam on his stuff. I simply can’t get it here at a price that makes sense. If you post your email address, I can send you the clark catalog. It is in a PDF format (you need acrobat or acrobat reader to view it, your computer probably already has reader on it, if not you can download reader for free at adobe.com). The first few pages of the catalog should give you the density information you are looking for. Let me know.
Here is the link. Just click on the link just below the first picture on the page. If you need reader the link to that is right next to it. http://www.fiberglasssupply.com/Product_Catalog/Blanks/blanks.html
Here is the link. Just click on the link just below the first picture on > the page. If you need reader the link to that is right next to it. I use 2.5 lb/ft3 EPS, supergreen is 2.7, the EPS is more ding resistant
Håvard, I know nothing about shear strength. What I do know: EPS is springier than PU. When you depress it, it springs back better. When you depress PU it tends to crush. Mind you, PU resists depression with more force per density. Epoxy glass is stronger than polyester glass. When you depress epoxy glass, it tends to spring back better. When you depress polyester glass it tends to crack and stay depressed. Polyurethane foam is a match for polyester resin. PU foam provides superior resistance to crushing, but when it crushes the polyester glass stays in the depression. PU foam is rigid but brittle. Crushed polyurethane foam loses its physical properties and turns to powder. The powdered foam loses its bond with whatever glass is above it. Only a weak glass, such as polyester-ed glass will retain the shape of the crushed depression. Epoxied glass will spring out of such a depression and appear to delaminate. In reality, the polyester glass merely delaminates in place over the depressed, crushed polyurethane foam. EPS provides less resistance to depression, but EPS requires less such resistance. When epoxy glass depresses into EPS, both glass and foam spring back together. When the depression force exceeds the epoxy/EPS ability to spring back, the system stays depressed. However, foam and glass tend to maintain their former physical properties without failing. But since the EPS is crushed, it becomes denser and stronger. Yes, you can glass with a lighter epoxy glass schedule. When glassing over EPS, you’re starting with a lighter weight material already. Why not take advantage of epoxy’s strength, and still have a lighter board. Otherwise your board will surely ding and take on water as all lightly glassed boards do. But instead of merely turning yellow like PU boards do, the EPS blank will absorb water until it becomes water logged. There are good reasons why the industry combines materials as they do. Why don’t you make a few different kinds of boards to test the industry’s principles?
I know the guys here who use epoxy glass their board heavy, atleast 2x6oz > bottom, 3x6oz top. Is beacuse of the properties of the epoxy or is it just > because of the EPS being softer then PU clark foam? The reason why I glass my boards this way is because of the vacuum technique I stil have the same weight as, when I not use this technique and have 2 x6 top and 1 bottom. The extra layers add a lot of strenght however and I like strong. Also EPS comes in different densitys and the good part is that you get the same density on the outside as on the inside. If you realy wanna build rockhard then use a thin hard foam on top of the shaped blank, vacuum this on the shaped blank and then glass it. Peter Rijk.