Prepping Gelcoat

Hi all,

I looked through the archives and couldn't find a specific post on how to proceed with painting the gelcoat. I am about finished with my wingtips and on to paint. The gelcoat surface is pretty good.

I am assuming that I should thoroughly wash it to get off any mold release or wax that might be present. Then go over it with maroon scotchbrite or similar to rough up the surface. I have been using Stewart systems. With other fiberglass parts (once sealed for pin holes) I have been using their high build, anti-UV filler followed by primer/sealer and then top coat.

Other than cleaning and roughing up the gelcoat, is there anything else I need to do before the primer/filler stage?

Thanks,
Michael Wynn
RV 8 Finishing

I thought I had read somewhere that most professional painters complete strip/grind off the gelcoat before painting.

Suggestion

I highly recommend that you block sand the gel coat with a very coarse sand paper. I have found "worm holes" and pocks under the gel coat. I had an area in the trailing edge that was approximately 2" long and was exposed after sanding through the gel coat. You can use a light inside the tip to see potential problem areas. The voids were filled with epoxy and micro filler and sanded. After completing a fill primer was applied and sanded to paint primer ready.

Better to find these areas now and not after you have a nice paint job applied.

The gel-coat serves no purpose except as a mold release.
It is heavy and should be sanded mostly away.

Mel said:

The gel-coat serves no purpose except as a mold release.
It is heavy and should be sanded mostly away.

Click to expand...

It does help you not sand into the physical glass cloth though.... probably more important with the older polyester parts.

So long, gelcoat

Thanks for the replies, guys. Looks like sanding, sealing and priming in my immediate future. It's funny, the gelcoat looks so good. Seems a shame to sand it all off, but looks like that is going to be the right thing to do.

Thank you all for your input.

Regards,

Michael Wynn
RV 8 Finishing
San Ramon, CA

From our experience in the composites industry, gelcoat on the cowls would add probably a couple of pounds or so to the weight, wing tips proportionaly less. It's primary purpose is to add colour to the product and is found mostly on products made from polyester or vinylester. There are coloured gelcoats that have been developed for epoxies but the colour range isn't as great and I don't think Van's uses them.

I would be cautious about sanding too agressively as there is a real possibility of exposing the fibres (not good). Use the gelcoat as a surface for fine sanding in preparation for priming and painting. By all means remove some if you want but personally I would leave most of it on.

Warming with a heat gun on a low heat or even a hair drier is useful for finding hidden bubbles and voids. The gelcoat will soften and the air inside will expand making them plain to see. Simply remove the gelcoat from the bubbles openning them up, roughen the inside surface of the exposed bubble and the area immediately around it using a dremel or similar, then fill sand and fair.

If you choose to remove all the gelcoat you will end up spending a lot of time filling and fairing the exposed weave of the cloth. I cannot speak about the later fibreglass items in Vans kits but on my own a/c (RV6 earlier kit polyester parts) the cowls etc needed a lot of work just to find and fill the voids.

It's sticky, dusty work but worth the extra effort to get a nice finish. Paint will only make any rough or uneven surfaces look even worse.

Clive Whittfield
Auckland
New Zealand

I give the gelcoat a nice sanding with 180 grit sand paper on a DA sander. Make sure the surface has no shiny spots. The gelcoat itself can stay. Next give it 2 coats of a high build primer like PPG K-36 or Akzo-Nobel AWL-QUICK. At that point your wing tip is good to go for paint.

When it comes to glass and paint, I give a LOT of weight to "KTM's" recomendations - he's done a LOT of RV's.....

KTM520guy said:

I give the gelcoat a nice sanding with 180 grit sand paper on a DA sander. Make sure the surface has no shiny spots. The gelcoat itself can stay. Next give it 2 coats of a high build primer like PPG K-36 or Akzo-Nobel AWL-QUICK. At that point your wing tip is good to go for paint.

Click to expand...

Thanks... that makes more sense than "take it all off"...

One Q. though -

If it's primed with AWL-Quick or K-36, can these be left when the plane is flown "naked" for a while, or should a top coat be added to prevent absorption of stuff before a full paint job?

az_gila said:

Thanks... that makes more sense than "take it all off"...

One Q. though -

If it's primed with AWL-Quick or K-36, can these be left when the plane is flown "naked" for a while, or should a top coat be added to prevent absorption of stuff before a full paint job?

Click to expand...

Awl-Quick is not suited for leaving an extended period of time but K-36 will be fine.

Status Update

Hi all,

Per the advice of KTM, used a DA sander and went over the entire wingtip with 180 grit paper. Put on three coats of Stewarts Ekofil high fill primer. Found just a couple of pinholes and irregularities to fill--all along the seams. The rest of the finish is smooth as silk. I will recoat with hi fill primer then prime and paint. Good advice. Thank you. Once I get the topcoat on, I will post a photo.

Regards,

Michael Wynn
RV 8 Finishing
San Ramon,CA

Thanks for the advise, which I followed...'kinda'.
I used high build primer over the 'filled' areas where I cut out the leading edge of the wing tip to fit VANs tip light inserts. The rest of the tip I hand sanded with 150 grit on a soft block. I sprayed thinned Pettit Easypoxy on it directly, and got a very good finnish, but I made one mistake on the first tip: I got fisheyes in a few places because I forgot to use a wax remover. The second tip turned out great!

Details?

ShipChief,

I am approaching the painting phase and am interested in the Easypoxy. What kind of gun and compressor did you use?
I am in Tacoma, so I would be interested to see your setup if you wouldn't mind.
Thanks.