I'm getting ready to glass my next boat, and being less than satisfied with the toughness of the last boat, I tested several glass types to get a better idea of what I want to use. Since I raised the subject, my last boat (http://www.metakrome.com/kayak/kframe.html) was a strip-built covered with 2 layers of 3.25 oz. satin cloth using MAS slow resin. My objective is to increase the toughness without significantly increasing boat weight. All of the samples below will build a structurally sound boat. But toughness varies.

THE TEST:
1. An 18" by 5/16 steel rod cut square dropped from 40 inches.
2. An 18" by 5/16 steel rod with rounded end dropped from 40 inches.
3. A large strait slot screwdriver dropped from 36 inches.

THE FABRIC:
1. 6 oz. plain weave left over from Pygmy kit.
2. 3.25 oz satin, 2 layers thick, from Raka.
3. 5 oz. satin from Raka.
4. 8.9 oz. satin from a local source.
5. 3.75 oz. plain weave s-2 glass, 2 layers thick, from Raka.
6. 6 oz. satin s-2 glass from John R Sweet.

Each sample had a sealer coat, saturation coat, and one fill coat (to better judge completeness of wet-out) of MAS slow resin/hardener applied to luaun plywood. Shop temperature was 60 deg. and resin temperature was 70 deg. The samples were hardened in a nice warm spot for several days.

THE RESULTS:
Each sample was judged for the depth of denting and amount of fiber cutting and whitening.

Sample One was clearly the worst of the lot. Most noticeable was much more whitening than any other sample.

Sample Two was somewhat better in all three criteria than sample One.

Sample Three dented and cut deeper than sample Two, but had less whitening.

Sample Four showed minimal whitening, better resistance to denting, and partially resisted cutting. Finally, some signs of toughness.

Sample Five was very very close in toughness to sample Four. It stood above only in resistance to whitening.

Sample Six was the only sample that passed the screwdriver test, and it passed very well indeed. No fibers were cut, just dented. Overall, whitening was limited to a few very small white flecks. This sample stood head and shoulders above the others.

DISCUSSION:
Originally I was going to weigh each sample and test for stiffness. Now that I have seen the impact test results, I've lost interest since Sample Six, the 6 oz. s-2 glass, performed so well. Assuming a 50/50 glass to resin ratio for the tight weave cloths and a 40/60 for the plain weaves, the six samples would weigh 15, 13, 10, 17.8, 18.75, and 12 ounces per yard respectively. So the second lightest sample was the toughest. And also the most expensive.

I was pleased to note that both s-2 glass samples wet out as clear as their e-glass brethren. However, the 6 oz s-2, as well as the 8.9 oz satin e-glass, is not for everyone. These two fabrics require a thin resin and good techniques to avoid the many micro bubbles that can plague projects made with these fabrics. I did pretty well with my left over MAS, but a later test with System Three Clear Coat shows even better wet out. Also note that I had absolutely no trouble getting the 5 oz. Raka satin cloth to wet out like some have stated on this board.

I find it curious that sample Five was not tougher than sample Six. After all, it adds up to a thicker composite. Others, including "He who must not be named" have espoused the merits of multiple thin layers of glass, but my limited test does not support this idea. Also, it is my impression that my boat with two layers of 3.25 oz. cloth cuts much easier than it should. That's why I went a-testing.

Will the stiffer s-2 glass give me nightmares when I try to get it to conform to a round hull rather than a nice flat plywood sample? I guess I'm about to find out.

Cheers,
Ted Henry