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For non-technical applications like this where the strength of the epoxy or
polyester resin/fabric composite is not an issue, you can significantly
shorten the post construction sanding/finishing time by adding a soft "filler"
to the resin to more quickly cover the weave pattern in the fabric.
Huh?
Typically, in structural applications, the ideal resin-to-fiberglas ratio is 1:1
by weight. There a special lay-up schedules to achieve this. Usually it
involves using non-woven mat between layers of woven cloth to lift the resin
content, and get better cloth-to-cloth layer bonding.
However, this is not the case in something needing little real strength like a
grill cover. What you want in this case is a quickly/easily/inexpensively
achieved surface that fully masks the weave in the cloth and be sanded
smooth for finishing/painting. The answer is to fill the resin with some
relatively soft material.
Like what? If you have access to a West Marine or other boating supply
house you could buy some "micro-balloons," incredibly small plastic
spheres. But you can just as reliably use stuff around the house; very fine
wood dust from sanding, baking soda, cornstarch, even plain old
cooking/baking flour.
First coat your fabric with coat of straight epoxy/polyester resin. You don't
have to go immediately on to the next coating. Just do not let the resin fully
cure. To get a chemical bond between coats, you need to apply the second
coat while the first is partially cured and slightly tacky.
Next thoroughly mix the two part epoxy/polyester resin in the correct
proportions. Then add you thickener-of-choice to get a consistency between
mayonnaise and peanut butter. Thinner mixtures will tend to level better,
but are harder to sand. Thicker mixtures build faster but result in a rougher
surface requiring more sanding. Brush, roll or trowel your filled resin onto
the fabric base. Strive for enough thickness to allow for sanding some away
to get a good smooth surface for painting.
Once the coatings have cured hard, sand away to get a smooth surface with
final sanding with 220 grit. Follow-up with 2 coats of primer (sand between
with 320), and two coats of top coat (sand between with 400 grit). A clear
topcoat is optional but desirable.
Most folks don't like to hear it but the longer you let paint harden and cure
in air before you put it into service the better. It wouldn't be a bad idea to
let your new grill block sit in a well ventilated place for a week before
mounting.
Hope this helps.
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