It sounds like the Elmers epoxy you got included some fillers (perhaps colloidal silica). Most likely it is formulated as a thickened adhiesive which will not run on vertical surfaces, or for use as a gap filler. For use in laminating layers of fiberglass, you will be best off with a clear 30 minute or slower formula. If you plan on doing a lot of glass work, you might look into the West System products. They sell a basic resin, then a selection of hardeners for various uses (quick, slow, extra slow) and a selection of fillers (microfiber, silica, graphite, aluminum). For making fiberglass parts and for glassing planes, I use the 105 resin and the 207 hardner. I also use thier metering pumps. There are a number of online sources, here's one:

http://www.cstsales.com/epoxy_systems-ss2.html

Scroll half way down the page for the begining of the West System products

Scott