: Good day all,

: I am constantly in need of information for weight of epoxy for a
: given layup. For instance: 4 oz. cloth versus 6 oz. What is the
: weight per square foot? Has anyone ever done a test similar to
: One Ocean's infamous epoxy durability test, but a test instead
: just to see how much stuff weighs. If only I had time and
: resources enough, I would do something like this:

: Test 1: Five pieces of wood, each 12" x 12" x 1",
: weighed before and after epoxying. Epoxy each with a different
: layup. Personally I'd like to see 3.25 oz, 4 oz, 6 oz, Double
: layered 3.25 oz, and double layered 4 oz. Then weigh each one
: after the layup and subtract the original weight. How much
: weight was added per layup?

: Before this was more a passing interest, but now I am building wood
: boards and kayaks for other people and especially for surfboards
: weight is a big issue with people. I feel it's a big
: misunderstanding that surfers have regarding weight, but I will
: spare you that dissertation. Anyway, so suppose someone wants a
: board and I say "Okay, I can use 4oz top and bottom if you
: want lightweight, or I can put 2x 3.25oz on the top for
: durability and you will add a little weight." First
: question out of their mouth- "How much weight?" My
: response, "Well, the weight of the glass cloth is 3.25oz,
: but each cloth soaks up more or less resin based on weight and
: weave so it's hard to say exactly how much it would add." I
: need better data.

: I have this kind of data for wood, and use it religiously on a
: regular basis. Wood "x" is "x" pounds/cu ft.
: If I use 1.5 cu ft. of wood "x" then I have 1.5x
: weight. I factor in a ballpark weight for glue based on the size
: of the project (for the latest 11-foot board I was shocked to
: use three bottles of glue!) and then I have to guess at the
: fiberglass. By this process so far I have guessed weights very
: accurately- within a pound or so.

: The next test I would like to do is a drop-ball durability test.
: There are standards for this set up somewhere by some governing
: agency because I know that when you ship sunglasses into the US
: you have to have a drop-ball form showing they passed the
: drop-ball test. It is a given weight dropped at a given height,
: which I believe is 6 feet. Anyway, no matter what height or
: weight, do a test to simply measure how big of a dent it made
: for given layups. I would think a 5 lb dumbell weight dropped at
: 6 feet would give a good idea of durability. I am not at all
: knocking Raka- I buy from them and I love them, but they claim
: their 3.2oz is close in strength to a plain weave 5oz. Well I
: want to see data. I want to test it and be able to know if I put
: 3.2oz Raka on a project I can give a customer some idea of how
: durable they can expect it to be. ... I used that as an example,
: but would like to see it for 4, 6, 7 oz as well. (I skipped 5
: because I had bad luck with 5oz cloth that didn't wet clear and
: I steer away from it.)

: Another test would be to take five or six different woods commonly
: used in kayak and wood board construction and weigh them before
: and after glassing. I know for certain that balsa soaks up more
: epoxy than mahogany. I have seen it first-hand when repairing a
: board. The balsa has a layer of resin-soaked wood going a few
: mils deep. The mahogany is just "coated" and not
: penetrated very deep at all. This one is really more of a
: curiosity, but we always say "Use wood 'x' because wood 'x'
: is lighter," but I've built using very hard, heavy woods,
: and gotten pretty lightweight end results. I believe part is the
: glassing schedule- for hard woods I can use lighter layup, but I
: also believe that the hardwoods don't absorb as much resin. I
: would like to do some tests on this.

: Anyway, before I go lathering wood up with epoxy for no reason, are
: there any tests of this nature that any of you can link me to?
: Any scientific data for epoxy would be appreciated. I already
: have volumes of data on wood!

: All the best, and sorry for constantly mentioning wood surfboards
: here, but both the kayak forum and the wood surfboard forum have
: a lot of talent and I am just being resourceful. The knowledge
: works the same for either application.

: Malcolm

Hi Malcolm,

Well it's harder than that. Depends on the skill of the person doing the epoxy. The ideal for wet layup (what we do) is 50% of the weight of the cloth in epoxy, so for 6 ounce for example the ideal would be 3 ounces of resin. Most can't achieve that without a dry layup which isn't desireable, the best most can hope for is 75% and the average is likely more like 100%. When I do weight estimates for boats and for epoxy use I use 100% and hope I'm wrong :)

If you were going to vacuum bag the layup you might get closer to the real ideal of about 33%. Only way to know how you do is to try it and weigh it. Will need a pretty sensitive scale to tell.

Btw, those weights are for a square yard, only fiberglass mat is weighed by the square foot.

Bill H.