Using epoxy resin/fibreglass?

[bookface]

Quick question for those who have experience with this. I've always stuck with polyester, because despite the smell, it's cheap and easy to use. However, I recently picked up some epoxy resin along with some powder bound mat to use with it, thinking I'd see if it was worth the extra. So far, I've found that the resin is almost too thick to properly wet out the mat, and getting it to follow the mould shape can be quite challenging. Despite my best efforts (and I never have this problem with polyester), air bubbles seem to pop up under the mat, separating it from the surface beneath. It probably doesn't help that I picked the fast set resin (doh!), and it's starting to gel before I'm really done, even when using quite small amounts of resin.

I'm using a 300gm mat, which I think roughly equates to 1oz. for the US folks, which isn't really that heavy at all. I've never really used the cloth, is that a better option with epoxy resin? Are there any other techniques that will help?

Any suggestions appreciated!

 

[robn1]

Make sure to use an epoxy made for laminating, it'll be thin enough to wet out the mat. I've been using Smooth-On EpoxAmite medium. Working time is 20 minutes. Cure time is 16 hours, which sucks a little but the quality is very high. And no stink!

 

[Zombie Killer]

I only use System 3. It is not cheap but quality rarely is. It takes a while to start gelling. I have never had any issues with the mat weting or air bubbles. It also takes at least 16hours to cure but i am never in that much of a hurry. I use a cheap 1" brush . I first brush on a coat then apply a sheet of glass cloth then you don't want to brush in strokes or it pulls the glass , i just get it wet with epoxy and tamp it with the end. Unless the part has multiple corners at different angles there are very few bubbles. I also usually use it over urethane. I use a urethane like TC1630 first to take care of details and build up the mold a little then back it with resin/glass for strength. I also stay away from fiberglass mat and use cloth. I have better luck with it and would rather take more time putting more layers down then mat. Mat also likes to leave pointy needles sticking up that get you when your not looking. I'll never use poly again, stuff stinks for years. Also you can put epoxy over poly but not poly over resin. There is something in the epoxy that inhibits the poly from curing where they contact each other.

 

[robn1]

Also make sure your glass is compatible with epoxy, it should say so on the label. Some cloth and mats have a binder that dissolves in poly, but will interfere with epoxy.

 

[bookface]

Thanks for the answers. The resin I'm using says it's suitable for laminating, but it's definitely a lot thicker than I'm used to. The mat is also epoxy compatible. Maybe I'll try and find a thinner resin, or try the cloth. The moulds I'm using tend to be fairly complex with lots of sharp corners and different angles, which makes me cautious about using cloth. Also, my experience with cloth has been that the edges tend to stick up where it was cut and it frays a little, is there any way of stopping this?

 

[robn1]

...my experience with cloth has been that the edges tend to stick up where it was cut and it frays a little, is there any way of stopping this?

I had that trouble too, that's why I started using mat. It seems stiff, but I roll it around in my fingers to loosen it up, until it gets soft and fluffy. You'd be surprised how flexible it can be. But if the mold is to complex, you can cut it up into small patches.

The EpoxAmite medium I use has a 650cps viscosity, it wets out both cloth and mat very well. I use acid brushes to tap it in. I do sometimes get an air pocket that won't work out, I poke it with a toothpick.