Smoothing-out gelcoat in a Fiberglass prop, how?

[GuntahKela]

Hey, guys:

I've heard all bad myths about working with gelcoats. Well, I need to smooth out a helmet that is covered with gealcoat. I tried sanding the gelcoat down, but it keeps clogging my sandpaper. If there a more effective way?

 

[MattMunson]

You can either just keep switching sandpaper, or add some water into the mix. There's nothing really particular about a gelcoat that makes it impossible to sand, it's just a material that handles a little differently than the resins you might be used to.

Hey, post some pics too! Would love to see what you're working on.

 

[cheech9898]

Like Matt said use a wet/dry sandpaper and water. Sometimes a drop or 2 of dish soap in the bucket of water will help too with keeping the paper from clogging. Also did you wipe the surface down with a solvent/thinner? There could still be a slight tac to some gelcoats, may want to wipe it down with a little lacquer thinner too. Other than that, if its large bumps/runs you may want to scrape carefully with a razor blade and if you don't know how thick the gelcoat is (especially around edges) avoid using too agressive of a sandpaper and accidently breaking through into the underlying fiberglass strands... some times finer grit and more sanding can be better. It can be hard to patch a breakthrough and get it to blend unless you do that whole section to the edges.

 

[JtotheP]

Once you get the skin layer of gelcoat off using lots of sandpaper you'll be able to treat it like any other hard surface. Some gelcoats when cast into the mold have the wax pull to the surface after curing--that's what's gumming up your sandpaper. Or the amount of catalyst in the casting was for slow curing or not enough.

If you want you could spray a high building polyester sandable primer over the helmet and have easy sanding. It binds to the gelcoat even without sanding the gelcoat first. It can give you an awesome finish as you work your way to higher grit sandpaper.

The primer can be found at any automotive paint supply and it takes MEKp (like FG resin) to catalyze it. Spray it out of an HVLP gun. Or you can even brush it on.

 

[Big_Water99]

Once you get the skin layer of gelcoat off using lots of sandpaper you'll be able to treat it like any other hard surface. Some gelcoats when cast into the mold have the wax pull to the surface after curing--that's what's gumming up your sandpaper. Or the amount of catalyst in the casting was for slow curing or not enough.

If you want you could spray a high building polyester sandable primer over the helmet and have easy sanding. It binds to the gelcoat even without sanding the gelcoat first. It can give you an awesome finish as you work your way to higher grit sandpaper.

The primer can be found at any automotive paint supply and it takes MEKp (like FG resin) to catalyze it. Spray it out of an HVLP gun. Or you can even brush it on.

Yeh What he said He knows his Gelcoats :thumbsup