Carbon-Kevlar board layup

jpeter · Joined: 18 Oct 2009 Posts: 353

Kevlar: On paper it's a great material. Stiffer and lighter than glass. More durable than carbon because it flex's a bit.
I built two boards using Kevlar about 20 years ago. A few things I learned:

1) You can not sand it ... AT ALL ... the fibers are stronger than the epoxy and sanding breaks the epoxy leaving fuzzy Kevlar which you are left trying to deal with using razor blade.
2) It wets out fine as long as you use a very thin epoxy.
3) 5oz Kevlar is really equal to 7 or 8 oz glass in terms of thickness and amount of material.
4) Kevlar is more flexible than carbon and will wrap around a rail better, similar to glass for layup workability.
5) Cutting Kevlar with scissors is difficult, you need to sharpen the scissors every couple yards you cut.
6) Put the Kevlar on the inside layer for layup.

I would agree with previous posts about using it for re-inforcements only. If I was building again I would use s-glass, no Kevlar or carbon on bottom. Maybe use some on top.

Jimmy lewis has recently posted some videos on board building that are great to watch. I went into this learning by my mistakes.

Buy good, thin epoxy, use a slow cure so you don't underestimate your layup time. Cure with slow heat.

Good luck, JP

isobars · Joined: 12 Dec 1999 Posts: 20935

U2U2U2 · Posted: Fri Jan 13, 2017 6:22 pm Post subject:

I use Kevlar, because I have it.

The discussion about sanding is true, since it's not a top coat, imo thats not a issue, once the epoxy coat is gone from it , the Kevlar starts to fray badly.
Yes it needs special scissors.

The thickness of the bamboo veneer would be the detail I would be interested in, that and cost.
.

rollerrider · Joined: 17 May 2003 Posts: 100

2 lb foam gonna add substantial weight on a big board. But does provide a little more stiffness. If you never used carbon or Kevlar before don't, its a pain. Bamboo is great stuff. Provides tons of stiffness. Have to vac bag it on. I built a 9'-6 wind sup with bamboo top and bottom. 2 lb foam. But heavy cause of 2 lb foam and one to many glass layers. I did not try to roll bamboo around rails. just used extra glass. Weighs about 28 lbs. Used bamboo from wood laminate shop https://www.certainlywood.com/ . They roll it up and ship it in a box. 14" wide so seam in middle.

U2U2U2 · Posted: Fri Jan 13, 2017 8:58 pm Post subject:

rollerrider · Joined: 17 May 2003 Posts: 100

Carbon patches are manageable but to do a full layup is not. It must be pre impregnated with resin on a large flat table (wet out with squeegee and excess removed) then transferred to the blank, trimmed while wet then vac bagged with peal ply and breather fabrics otherwise it will take on way too much resin, way more than glass. This is why it costs so much. Not just the material but the process is more expensive.
2 lb foam gains little in compression strength compared to 1 lb (heal dents) and in a large board will gain 4 to 5 lbs on a already doomed to be heavy home made board.

U2U2U2 · Posted: Sat Jan 14, 2017 10:58 am Post subject:

The gain in weight from 1lb EPS density for a 150liter board over a 2lb is 4.95lb. Using 1 lb of EPS at 1.5 kg, 2 at 3 kg. Your weight is basically correct.

The gain on a 100liter board would be 3.3lbs, for the 1lb version, you would add at least 2.2 lbs, of corecell/ divcell/airex and glass -resin.

Your carbon usage involves avlarge area, like the entire board. It's used to reinforce needed areas , not cover, my method.

The difference shaping 2 lb EPS vs 1 lb is huge, 2 lb is easy, 1.5 may be a compromise , but still a pita to shape.

We take all the pieces of the puzzle and fit to each other's likening.

U2U2U2 · Posted: Sat Jan 14, 2017 12:16 pm Post subject:

https://www.wired.com/2015/07/rocket-scientist-designs-stronger-lighter-surfboard/

This was cost prohibitive to me. The blank was not thick enough, a custom cut would be even more costly.

http://varialsurf.com/

During my conversation with them, some guy named Keith, from Maui had ordered one. Never followed up anymore.
For a shed or garage builder a lot goes towards local, ( no shipping) a Cnc machine, and cheap in comparison to other options.

thombiz · Joined: 25 Jun 2007 Posts: 799 Location: Corpus Christi

Thinking about 2 lb density EPS brought up some questions. First, why not use a big surfboard blank and glass it like a surfboard instead of using EPS. Foam surfboard blanks range from about 1.8 lbs density to about 2.8 lbs density and they come somewhat pre-shaped. I can see shipping being expensive, but so is shipping EPS. A surfboard blank would be much easier and cheaper to glass using polyester or vinylester resins. The structural properties of the surfboard blank foam would be substantially higher than EPS.

I used 2 lb EPS foam on one board and have regretted it ever since. You just can't offset that kind of weight using every "weight reduction trick in the book".