What filler material to add to vinylester for filleting.

I am putting my stringers back in my hull pretty soon and I wanted to see what should I be using to add to the resin to thicken it up so I can pull my fillets. I hear contrasting things. I was planning on using chopped 1/2" fibers and cab o sil, but that may not be the right things to use.

 

The cabosil is what you need. Chop strand will slightly increase the strength, but not really enough to concern yourself with. Other things may make it lighter and/or easier to sand, but that's it.

Cabosil (silica) will thicken it plus keep it from sagging, other fillers won't do that, it may be thicker, but it will sag.

Fibers make it marginally stronger, but harder to work with, the more you add the worse it gets.

 

Silica works fine. It makes it really smooth and easy to spread. I usually mix a large batch and then add catalyzer as needed.

 

I use a blend of milled glass fibers and cabosil which makes a smooth paste, if anything makes it more difficult to work it is the silica, I buy it in the big bag, 10lb I think and it is often a bit lumpy but smooths out with enough mixing. The fiber does not make it any harder to sand than the silica alone and if it is a structural filet I am usually laying the glass into the wet filet anyway.

Steve.

 

Well blended silica makes a very smooth mix, talc makes it even smoother. Milled fibers, any fibers actually, make it more difficult to work with. Adding enough fiber to actually increase the strength to any great degree makes it difficult to work with. I'm not talking about sanding.

We make putties.

 

Milled fiber makes a very smooth workable paste but it still needs silica to keep it from slumping. There are very few addatives that don't require silica, systems three sells a ground up polyethelene addative that makes a nice thixotropic paste and of course wood flours but not many others come to mind.

 

There are various lengths of milled fibers, and then the longer chopped fibers. The shorter milled fibers don't affect the workability of the putty as much, the more you add the worse it gets though. They also don't offer much strength, the longer the fiber the better the strength, although the additional strength is still limited because the fiber content in the putty is still very low. what you end up with is a lumpy hard to get smooth putty that is only marginally stronger than without the fibers. So unless strength is required for the application it's just as good to not use fibers.

 

When making any mix, first add catalyzer, mix well, then the rest.

Dino

 

The load goes first and then catalyzer. This is vinylester resin.

 

So put the cabosil in the vinyl then once that's mixed up well add the catalyst? I used to do it the other way with poly, what's the reason it's different for the vinyl ester resin?

For those curious, I am only using the fillets so I have a nice radius for the 1708 to stick to when tabbing my stringers in.

 

There is no difference between the two. Normally a large amount of putty is mixed up at one time, enough to do the entire job, plus some. This way all the putty is the same, and unless you are using just a very small amount it's much quicker.

You can also get much better blending of all the ingredients if you can take your time while mixing. Leaving it sit also allows the resin to more thoroughly wet out the silica and other items you may add too. Use a 5 gallon bucket and add about 2.5 gallons of resin, then add Cabosil and whatever else you want to achieve the consistency you desire. Mix it with a drill motor and mixer attachment. There is no exact amount of each item because it depends on the exact resin you use, plus how you plan to use it.

We sell it in pails and drums, it's all premixed and ready to catalyze.

When using epoxy it's easier to mix both parts together and then thicken it due to the amounts of each portion, plus you typically have a much longer gel time.