It seems that my P/U board is stronger than my epoxy board. I used one layer of four ounce glass cloth on the bottom of both boards. I can push my thumb down on the bottom of my epoxy board and it will make an indentation, yet, when I do the same thing on my P/U board, no indentation is made. Now, I know I can add more layers of glass cloth or use a heavier cloth, but wouldn’t that add weight to the board, which would be be contrary to our intentions of making a lighter board?
That’s a tough call Tony.
I can’t say for sure, but it sounds like your epoxy might not have fully reacted, which is hard
to measure, so I am just suggesting it. An epoxy glass job that has gone to completion is
quite stiff and strong.
The logic you state makes sense for given equal blanks. I think the intent of using epoxy for more
strength is to use a much lighter core, then focusing on making the skin thicker and much stronger.
By comparison, polyester is at its best with thinner skins and heavier cores relative to epoxy.
Lastly, the polyester boards have evolved to their (near) optimum. When epoxy boards are built
the same way, they are most likely not near their optimum. Making epoxy in the same paradigm can
be considered a dead end effort- exploit the strengths.
[b]"epoxy versus polyester "
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[/b]this is the first time I have said this …
“SEARCH THE ARCHIVES !!!”
ANY " ***************** vs********************** " threads should be banned before they even get started !!
[b]
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PlusOneShaper, you stated that the resin may not have fully reacted. Does this mean that it has not fully cured? If this is the case, how long will it take? I have just glassed it within the last few days. Your responses are always very informative and appreciated.
The mixture ratio may have been slightly off (epoxy is very sensitive to this).
Did the temp drop much below 70F in the last few days? and more importantly
what was the temp while doing the work and for the hours following?
You might be able to post-cure the epoxy, depending upon how much torture
the construction method can handle. Depends upon the brand and speed of the
hardener used, but 8 hours at 120F is an example, or 3 days at 90F, etc.
just mu 2 cent
If the blansk were the same I’d go with Plus ones advise.
But the resin might not be the issue. you never said if the blanks were identical. If you are comparing a PU/PE board to an EPS/EPX board the density of the eps foam could be to blame.
Check Gregs chart on the glassing schedual for the diffrent density foams. The stuff you get in the hardware shore is probably only 0.7 ot 1 lb and needs more glass.
This may be overstupidifieng things but this soft epoxy sometimes happens to me too. Comes from sanding too soon after glassing or just sanding off too much of the hotcoat and leaving the resin too thin. well glassed epoxy eps is solid.
cheers
I also wonder why a lot of people use the light glass schedule of 4oz bottom and 4x4oz top with epoxy. On short boards ; sub 6’ to 7’; I have been going with 6 and 6x6oz and I get a strong feeling glass job, (no pressure dents yet after a couple months surf{admit, not every day-- weekends) and the boards are still lighter than some PU boards that friends have.
I actually have an Egg that is 4x4 , 4x4x4 and at 6’8" it is still lighter than a friends Stewart fish… I think it is about 5’11". For info, I use 2# EPS with a 3/8" basswood stringer, and so far gloss coats on all the boards.
Is it really necessary to go with a super light 4 , 4x4 glassing? Sure it will be even lighter, but if it compromises strength??
And that is if the problem isn’t because of mismixed epoxy or foam that is not dense enough.
some of the strongest EPS/Epoxy boards I’ve seen were Greg Loehr’s personal boards. They were 4,6 bottom and 6/4/(with 2/3, 4) deck. It was some time ago and I think it was 1 lb or 1.5 lb foam. He also made the outer glass 4 ounce on both sides as it uses less hotcoat resin…
…seems that “mis-matched” cloth is stronger/stiffer and light cores with stronger skins do quite well.
That makes a lot of sense. Kind of like how snowboard manufacturers us cross ‘grained’ glass , 45 degrees one way and then 45 the other. The ‘unmatched’ weave will make a stronger composite.
I remember reading somewhere that you ‘should’ put the lighter glass under the heavier glass. Be nice to save on hotcoat resin though, what with the cost of Epoxy.
I think that it is possible that the resin did not cure yet, The first time I glassed with epoxy it took a little over 2 days before I could not scrach a little dent in the resin with my thumb nail.
Cheers.
Quote:
That makes a lot of sense. Kind of like how snowboard manufacturers us cross ‘grained’ glass , 45 degrees one way and then 45 the other. The ‘unmatched’ weave will make a stronger composite.
Hi Johan,
imho the word strong is a bit misleading here. In snowboard construction, the fibers have to deal with “twisting” forces, so they are aligned in various directions to use their tensile strength to the max. However, denting is not determined by the fibers tensile strength (unless you have concave decks).
But, like Rhino said, epoxy needs time to cure. Read the manufacturers data sheets. They suggest up to two weeks at room temp, or a post cure…
Quote:
Quote:That makes a lot of sense. Kind of like how snowboard manufacturers us cross ‘grained’ glass , 45 degrees one way and then 45 the other. The ‘unmatched’ weave will make a stronger composite.
Hi Johan,
imho the word strong is a bit misleading here. In snowboard construction, the fibers have to deal with “twisting” forces, so they are aligned in various directions to use their tensile strength to the max. However, denting is not determined by the fibers tensile strength (unless you have concave decks).
But, like Rhino said, epoxy needs time to cure. Read the manufacturers data sheets. They suggest up to two weeks at room temp, or a post cure…
if you wanted to take advantage of that level of tensile strength go for a multiaxial weave with aramide fibers, it may be too much for a surfboard though… windsurfers and kiteboards use it for high velocity impact stregth, with success.