epoxy fillers

Hi all
I'm becoming quite familiar with epoxy fillers with my ply/epoxy/glass project. I have a couple of questions.
1. a fairing filler for laminating.
it way be the wave I'm using but after laminating, my surface is not smooth. I'd like to squeegee a fairing mix thinly over it. I had some west 404 which gave a nice smooth easy to apply mix. But its a special purpose product. I want something that handles well and goes on smooth - cabosil goes lumpy like oatmeal. And I want to be able to sand it, so talc/rockdust is out. Its also heavy. Likewise milled glass, which I use all over in structural joints. Microballoons make the stuff flow like ballbearings - so not useful on non-horizontal surfaces.
2. I'm a bit suspicious of wood flour. I *think* it compromise one of my structural joints, the mix just stayed gummy. Any ideas about phenols etc and epoxy?
thanks
A

 

The wood flour gummy thing is not a fault of the wood flour. Cabosil with microballoons can get you a nice creamy mix if you power mix it. If your hand mixing then you aren't going to have as smooth a mix. Also mix your fillers together before adding to epoxy. Blending fillers always works better than just one or the other.

 

I'm not sure I understand your question, but West 404 isn't even remotely intended to be used as a fairing compound. It's made of decomposed limestone and silica, both of which are pretty tough things to sand. For the novice user, you'd be best advised to use System Three's "Quikfair", which is a smooth premixed fairing compound that cures quickly and spreads uniformly. If you must mix your own, Q-cells, micro and phenol balloons, plus a splash of talc and a touch of silica to control viscosity is the way. Some experimenting with ratios and you'll develop a premix that you can add resin to, with consistent results and common properties.

 

thanks Par. I'm like to try DIY, and talc sounds like the thing. Sandable (odd since its rock), smooth,inexpensive. But there are warnings not to use it below water level. Why? Same is said of Q cells. But not phenolic balloons. As for the 404 I had a bit laying around and just mixed it in as a test.

 

Talc can be added to anything to improve its "sandability". Lots of minerals and even stone are very sandable, if the particulate size and physical composition are appropriate. Q cells and phenol balloons are often the same thing. They can be made from silica, quartz, acrylics, etc. and often are sold this way. As a rule phenol balloons are lighter and easier to sand, but I don't use these below the LWL unless over coated, with straight epoxy and preferably only on trailer borne boats. Moored boats should have a more generous epoxy/paint over coat, though plenty of boats have used these materials in huge amounts under the LWL. Mixing your own is a trial and error process, but eventually you'll get a combination that you can repeat.

 

PAR, thankyou!
>Lots of minerals and even stone are very sandable
right, particle shape is as important and hardness
> Moored boats should have a more generous epoxy/paint over coat,
makes sense
What about inert, non hygroscopic, non mineral fillers? I'd wondered about groundup car tires, or groundup plastic bottles etc - probably available from recyclers...

 

All things you can think of have been added to goo. Plastic bottles will likely have an adhesion issue, while automotive tires will usually have bits of metal mixed in.

 

Keep track of your filler & fairing recipes, along with your evaluations of them with regards to sanding, so that things are consistent. And don't forget to factor atmospherics into things. Not just ambient air temps, but the temp of that which you're applying things to. As the added or subtracted heat from the material that the compound is being spread over can be a factor. Ditto if it's in direct sunlight or not. And something like a cored composite won't suck or add heat as fast as a solid, like wood. What I'm saying, pretty much, is that the same rules & techniques for getting a perfect clear coating with neat resin, apply to varying degrees even when fairing.