Interesting but you left out some important details on the CF you used. Who made it and what was the yarn type? Loose of tight weave? This would help to clarify the results greatly.

There's a plethora of CF out there and I've used them all and each has a characteristic unto itself-and some are non-starters. Some CF yarns are so flat that they are referred to as "tape" (Amoco and some Hexcel). Some are what one rep called "round" and I've found many that are comparable in epoxy requirments as most fiberglasses of comparable weight. However, the advantages of CF lies not with the epoxy take-up (this is a variability from minimum required to the degree of excess that is present), but in its intrinsic strength over nearly everything else.

Tonight we laid approximately 20 oz of BFG (Amoco as the CF source)5.7 oz 2 by 2 "loose" weave CF using 17 oz of epoxy and scraping up approximately 3-4 oz of excess epoxy from the inside of a S & G Night Heron. The squeeze out of epoxy measured as just over 4 oz in the measuring cup however, the epoxy had some air in it from the squeeze out, it's sitting in the cup tonight to see if it settles. (The substrate was 4 mm okoume plywood with a seal coat previously applied and roughed up a bit before CF application.)

So, with that data, the CF took up less then it's weight in epoxy, though there is variability in that the exact yardage of CF is estimated from the plans penciled out tonight. The less-then-the fabric-weight take-up is due mostly to the specific CF fabric selected, and somewhat less in the application technique and experience using lots of CF. There's a real trick in using CF that does takes a lot of practice, and like I mentioned above, there's many kinds of weaves and yarns. I want to stress the point on practice, with or without vacumn-bagging, it takes practice. That said, I'd like more info on the CF used in your test for my records.

You brought up an interesting question on unidirectional CF and it depends on the yarn and tightness of application. My paddle female area I strengthened using CF yarn wound on with periodic wet-outs. The excess squeezed out on it's own with the wrap. This yielded a highly reinforced paddle in that critical area that has weathered some serious abuse. I haven't tested anything using a gauge but this has sparked my interest to quantify this method.

Looking forward to your reply and would like to record the results for my records (with your permission of course). I like your methods in testing, well thought out and conceived. Real good data without doubt.

: I performed an experiment yesterday which I hope will add clarity to the
: recent thread on the light weight nature of carbon fiber. Two conflicting
: ideas popped up on that thread. One was that carbon fiber fabric of the
: same weight as glass will generate a laminate of heavier weight simply
: because carbon fiber being less dense makes a fabric that starts out
: thicker and thus soaks up more resin. The other idea was than carbon,
: maybe because it has fibers packed together better, does not soak up more
: resin. I am talking about applications using hand lay-up, not vacuum
: bagging. And the superior stiffness of carbon fiber is not in question.

: I measured and weighed three samples of 6 oz. woven CF, 6 oz open weave E
: glass, and 6 oz. satin weave S glass, both before and after applying
: resin. The samples were placed between two layers of plastic film where I
: squeezed out excess resin from the cloth with a roller. The final samples
: contained no substrate, only cloth and resin.

: The 2 inch square cloth dry samples of CF, E glass, and S glass weighed 8.2,
: 8.2, and 8.0 grains respectively, and were .16. .07, and .06 inches thick
: (using my cheap caliper). So they were all very close to being the same
: weight and all very close to the advertised 6 oz. cloth weight, regardless
: of thickness.

: After cure the samples were cleaned of squeeze out and peeled from the
: plastic wrap. The same samples now weigh 23.5, 18.5, and 16.0 grains. The
: CF sample weighs 47% more and the E glass sample 16% more than the S glass
: sample. The S glass sample yielded a 50:50 ratio by weight. I don't assume
: that these numbers represent the absolute numerical relationship between
: these fabrics due to possible errors in my methods, but the different
: weights among the samples in too large to ignore and also matches well
: with my experience. Carbon fiber is really stiff, and has many good
: applications, but it may not be as light as you expect without using
: advanced techniques like vacuum bagging. Satin cloth yields a lighter
: lay-up than open weave cloth, but not by a great deal.

: One question is still nagging at me. Is it possible that unidirectional
: carbon fiber, with fewer and or smaller gaps between the fibers, yields a
: much less resin rich lay-up?

: Ted