Is 1 layer of 18 oz. fiberglass just as strong as 3 layers of 6 oz? Thanks
Nope.
I don’t know the formula off hand, but three layers of 4oz will be significantly stronger than one layer of 12oz, and measurably stronger than two layers of 6oz.
I second the NOPE.
I would say NOPE too.
Glassed a 14-6 paddle board made with 2 lb. poly foam with 10 oz. instead of double 4 or 6 and all I got was a heavier board than I wanted that is more fragile than expected.
Think you’re adding weight - with probably less overall strength - using 18 oz.
Pete
Thanks! Does this hold true say…for 5 layers of 2.4oz is stronger than 3 layers of 4 oz?
Apeek,
Maybe it helps to think about it this way: the laminate is basically going to be stronger when the gaps between fibers is at a minium (and the laminate is well impregnated with resin).
Since all the glass is basically woven, the heavier the weight of the cloth the thicker the section of strands that make it up (roughly 3 times on 18 oz. vs. 6 oz.). You can think about woven baskets you have seen or even ropes of different thickness being woven.
With a more coarse (thicker, heavier) weave you end up with a higher ratio of resin to glass fibers to fill all the gaps in the cloth. As the glass flexes the areas of resin only can get little micro cracks. Essentially, this extra resin is just filling the voids but not providing much structural integrety.
Lighter cloth = tighter weaves and better resin to glass ratio, less gaps in the matrix, less (almost) useless resin, etc.
Of course there can be diminishing returns. 2.4 oz is not as easy to work with as 4 oz IMO. 2.4 does drape pretty nice and wet out easy, but it shifts around and is harder to pull tight. Getting 5 good layers down is not as easy as getting 3 layers of 4 oz.
Yes, the more layers of cloth you have, for a given weight, the stronger it is. One of the few instances where ‘‘some is good, more is better’’, is really true.
Thanks for the help, the rope analogy really helped me understand.
Sorry to be asking to many questions. But On my next board I’m building, a 5-6 fish, i’m using 1lb eps foam. Generally most recommend using 3x6oz deck and 2x6oz on the bottom.
From what you all have said and what I understand it to be. Using 4x4oz deck/3x4ozbottom. Would Glassing the board this way would yeild a stronger board?
Quote:
Yes, the more layers of cloth you have, for a given weight, the stronger it is. One of the few instances where ‘‘some is good, more is better’’, is really true.
precisely. think of it this way. strength comes from fiberglass…NOT from resin. lower weight cloth has a tighter weave…and, therefore, less resin per ounce of fiberglass in the lam. heavier cloth has a looser weave, and will take on more resin in the lam. so, from a strength-to-weight ratio perspective…more layers of lighter cloth will provide greater strength than fewer layers of heavier cloth.
strength comes from fiberglass…NOT from resin.
Yes and no.
Depends on what ‘strength’ youre referring to. If its tensile, then yes…if its compression then no. The tensile strength of the laminate is NOT the weakest link, compression is and glass in compression is worthless without the resin. There are other weak links too not related to tensile. The ‘stiffness’ of a laminate governs compression failure resistance. Many/most early board failures are due to compression/buckling failures…for the umphteen time 
i’ve found that minimizing excess resin in the lam gives me a stronger board. i glass with epoxy, and generally use RR-2000 for the lam, and then slap on a hotcoat and gloss with RR-2020 for added compression strength. extra resin in the lam doesn’t seem to give any more compression strength…i prefer to let the hotcoat and gloss absorb the shock from the bumps and bangs here and there. some of the boards glassed with the 2000 lam / 2020 hot+gloss have been ridden pretty hard over the past few years and don’t really show dings or any sign of failure in the near future.
The crossing of the weave on multiple layers will add strength too, go find a friend that knows karate, get three wooden boards and stack them on top of each other with the grains flowing the same direction then have him chop them, now get three more and stack them with opposing grains then let him have a whack, I’ll bet he prefers the like grain stack every time.
Matt Kechele tried pulling the cloth (to change the weave pattern) on a board one time and the board broke in crescent shape because both layers pulled the exact same distance and the grooves between the weave matched to make a weak point.
crazy, matt. he was in SurfWorld awhile back and dropped what had to be the meanest deuce the history of man has every seen (or smelt). cleared out the whole shop. i think the department of health shut 'em down for a week as a biohazard.