Filling the bondline: foam or epoxy?

[beachedflunkey]

I've been using epoxy w/silica filler. I'd think that'd be a little stronger than foam and only add a pound maybe. But maybe foam is easier or faster to sand smooth? Who's using what?

 

[Frosty]

I've been using epoxy w/silica filler. I'd think that'd be a little stronger than foam and only add a pound maybe. But maybe foam is easier or faster to sand smooth? Who's using what?

I used foam in my SN... Newman used foam in his RN. Definitely much easier to sand. But most likely not as strong as resin/hardener/silica. Not sure which way I plan to go on my RN this winter.

 

[newman]

from an engineering standpoint what you are concerned about is a high moment of inertia. looking at a cross section, the area filled with foam or epoxy is very close to the center of mass of the CS. Yes, the epoxy will add more strength, but it will actually add very little... it's not so much about weight as it is about ease of installation.... foam is much easier and far outweighs the benefits of epoxy. Also, keep in mind that just epoxy and silica will provide very little strength without hair. Injection molded plastics with even 10% glass are nearly twice as strong... think of it like breaking up a clump of mud or a clump of sod... the sod is much stronger, because of interlinked polymers.

 

[SJBrit]

I would foam and glass a couple of layers over for strength/durability of the foam. Here's why: once you've added a scupper or two, a front exhaust, some footholds etc, you actually end up removing a LOT of buoyancy from your ski. Watching Paul (Lehr) hang on to his sinking ski in Texas made me realize the value of adding foam wherever you get a chance.

 

[Waste Land]

I would foam and glass a couple of layers over for strength/durability of the foam. Here's why: once you've added a scupper or two, a front exhaust, some footholds etc, you actually end up removing a LOT of buoyancy from your ski. Watching Paul (Lehr) hang on to his sinking ski in Texas made me realize the value of adding foam wherever you get a chance.

Foam it is!

 

[newman]

eh, the amount of foam that actually remains i VERY small... the most on either side of the handpole, if you chose to do that... volumetrically speaking it probably equals a scupper+footholds.

 

[beachedflunkey]

And foam all the way up level with the handlepole mount base? I know I usually get a good amount of resin buildup there.

Age old question: 2lb, 3lb, 4lb, canned, or does it really matter? You just want something to build up a base, correct?

 

[SJBrit]

eh, the amount of foam that actually remains i VERY small... the most on either side of the handpole, if you chose to do that... volumetrically speaking it probably equals a scupper+footholds.

A new superjet with dry foam barely floats with the back corner sticking out. When you pull out a significant volume of foam when you mod it then you are risking having problems. Add a little water retention to that and you've got yourself a sinker. Even though the amount of foam is VERY small, so is the flotation margin even on a stocker. Every little helps.

 

[Marshj]

Personally Ive done a few skis. and i feel that the silca mix really iseasy to work with in the bondline. much easier than i see foam being, because there is no need to wait and sand.

I shape the filler how i want it with a tongue depressor and lay the glass/carbon over it while its still wet/tacky. This way its a chemical bond, not a physical bond- much less likely to delaminate on a hard impact. food for thought

*edit:

On many reinforced superjets the reinforcement does not go all the way to the inner lip of the hoodseal (from top to bottom) I feel that it is important to add silica filler/epoxy under the curve of the hoodlip, and continue the reinforcement all the way to the edge. The most common spot for RN sj's to crack is where the stock rivets hold the fuel lines.

 

[T-bone]

foam....them west sysems some layers of glass over it. the only problem is no to build it out to much ....that pesky factory pipe need to have clearance.

 

[hangtime]

I used epoxy on mine and layed in the cloth over it while still wet like marshj said and that creates the best bond .I do appreciate the idea of added faom though I foamed the entire nose of my ski .

 

[jetskier79]

I used filler......layed in wet is the best/esiest way to go in my opinion....even easier than foaming. One downside is the possible added heat. When I layed up the glass in the nose.....I layed in filler and then glass right over it while it was wet. I mixed the filler a little hot, that added heat set off the glass sooner than I had hoped. But as long as you don't mix too hot, you shouldn't have an issue

And I think marshj is spot on about reinforcing the hood lip. I used filler to smooth out that entire area, including filling in all the rivet holes. My reinforcements come all the way up.

 

[SUPERJET-113]

Epoxy baby!

 

[yamaslut]

no foam.....

1. I lay the ski on its side
2. sand w/ 36 grit
3. cut up a bunch of matte and fill gap
4. mix up epoxy, silica, glass beads
5. pour it, then lay my carbon over that and let it dry
6. repeat on other side

 

[FL-cracker]

Im lovin the sig!^^^^^^^^ Good info on this thread as well.

 

[LBE]

On many reinforced superjets the reinforcement does not go all the way to the inner lip of the hoodseal (from top to bottom) I feel that it is important to add silica filler/epoxy under the curve of the hoodlip, and continue the reinforcement all the way to the edge. The most common spot for RN sj's to crack is where the stock rivets hold the fuel lines.

Well stated, a weak point commonly overlooked.

then lay my carbon over that and let it dry

pish!