Best way to cut GRP?
 

I need to cut the return lip down on my rear arches to clear the rear tyres - what's the best way to do it?

Should the exposed edge of GRP be sealed?

1mm steel cutting disc in an angle grinder, gives a perfect cut. You don't need to seal it. I make motorcade seats out of GRP and find that the cut edge of GRP just soaks up the paint, so much so that by the time you have a decent amount of paint on the edge the rest of the panel has so much paint on it that it looks like the surface of the moon.

I simply go over the cut with a Black wide chisel tip pen at 45 degrees, takes the "whiteness" away from the cut GRP.

I'd seal it with some GRP layup resin - given that it soaks up a lot of paint it would also soak up water? which when it freezes will damage the GRP.

I use gelcoat. Layup resin, gelcoat, or a skim of body filler will all work. The idea is to seal it from water intrusion. I really prefer gelcoat applied with a narrow brush. This allows a bit of extra material that may be easily sanded.

The other way is to use a flap wheel is an electric drill so you can follow the profile of the arch without having lots of short cuts from a cutting disc.

Either way use a good mask or you with having chest problems for a month !

I use a dremel cutting disc, then tidy up with a sanding drum on the dremel. As above, use a mask, every time I forget I get a bunged up nose for a couple of days.

Its worse than that . I ended up coughing blood and a lung infection ! That was from less than two hours with a cutting disc on GRP.

Bloody hell - this sounds dangerous!

The other options (avoiding high speed dust manufacture) are a hacksaw blade, or slightly faster (but not as accurate) one of the tungsten carbide grit blades, used by hand.