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Fiberglass Crazing Fix?

rockitdoc

Well Known Member
Sponsor
My wheel pants have crazing? in the gel coat around the aft edge of the forward fairings. Seems like it's just in the gel, not through the glass, so prolly not structural, but it looks bad, to me.

Anybody else have this issue and what did you do to fix it? I was about to epoxy with micro over and sand it back, but then thought of asking first.

S

Wheel Pants Crazing.jpg


Wheel Pants Crazing 2.jpg
 
Cracks

Looks like the gel coat is cracking. I would sand down and apply micro or a high build epoxy.
Maybe Dan will chime in.
 
It's polyester gel coat. Polyester shrinks. Sand it off, re-finish.

For the record, I wish Vans would return to bare glass, no gelcoat. A little whining about the need for pinhole filling will be nothing compared to the shriek when $20K paint jobs go to ****.
 
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It's polyester gel coat. Polyester shrinks. Sand it off, re-finish.

For the record, I wish Vans would return to bare glass, no gelcoat. A little whining about the need for pinhole filling will be nothing compared to the shriek when $20K pain jobs go to ****.

Dan
Does the gel need to be completely removed thru the shrinksge cracks, or can i just rough it up with 60 grit and cover it with epoxy and 410 ?
 
Dan
Does the gel need to be completely removed thru the shrinksge cracks, or can i just rough it up with 60 grit and cover it with epoxy and 410 ?

The gel coat is very thin. You can sand it down until you see the translucent filberglass underneath. I use 80 grit to to reduce the hatchmarks from the sandpaper action.
 
The gel coat is very thin. You can sand it down until you see the translucent filberglass underneath. I use 80 grit to to reduce the hatchmarks from the sandpaper action.

I will sand until no shrinkage cracks are visible. I would gate to do all this and have the ‘crack’ show thru the paint.
 
Polyester

It's polyester gel coat. Polyester shrinks. Sand it off, re-finish.

For the record, I wish Vans would return to bare glass, no gelcoat. A little whining about the need for pinhole filling will be nothing compared to the shriek when $20K paint jobs go to ****.

Wow! Learn something new every day. I will quit complaining about my pepto cowl. I'm gonna be pissed if my wing tip pain cracks!
 
Recommendations

So for those of us building 30 year airplanes, when we are doing the fiberglass work during the build, would you recommend we sand down the gel coat, fill any pin holes, and then just re prime while awaiting paint?

Looks like I will need to remove gel coat anyway if I wish to build up a section for better fit. Thanks for telling me it is polyester (ugh)
 
I have a 30 yr old kit with white gelcoat. I hate gelcoat. It is heavy and prone to cracking. I sanded it all off. There is a lot of gelcoat on an rv4 cowl both in terms of surface area and thickness. I used power tools and did my best to catch all the dust. I got about half of it. My shop looked like it had been hit by a snow storm but I was rid if the cursed stuff. I applied west system and micro, then after restoring countour more straight west system, hit it with heat, then squeegeed it off to fill any pourosity, cloth weave or pin holes so basically a sealer. That worked well. I will used a high build epoxy primer prior to paint. Lots of work but woth it in the long run.
 
If i sand off the gel coat, do i need to apply epoxy and 410 over it or can i just primer/filler, sand, prime and paint?
 
You apply epoxy primer over the fiberglass and paint on top. The main issue with the polyester gelcoat is when it was applied very thick over the mold and caused surface finish issue. In most cases, it is very think and some light sanding will remove most of it. Also, you will have to sand off the top gelcoat surface with coarse sandpaper prior epoxy primer in order to achieve good mechanical bonding. You may not have to sand off all the gelcoat because the layer is so thin, except for a few area.
 
You apply epoxy primer over the fiberglass and paint on top. The main issue with the polyester gelcoat is when it was applied very thick over the mold and caused surface finish issue. In most cases, it is very think and some light sanding will remove most of it. Also, you will have to sand off the top gelcoat surface with coarse sandpaper prior epoxy primer in order to achieve good mechanical bonding. You may not have to sand off all the gelcoat because the layer is so thin, except for a few area.

Good news! I was not looking forward to applying West Systems with micro over the sanded gel coat. I will just scuff the glossy gel coat and apply epoxy primer.
 
Gel coat is for hot tubs. Ha ha. Gel coat will more likely crack at some point and adds weight. Early white gel coat cowls RV4 and RV6 were crack-O-matic. Things like gel coated wing tips are better since they don't live in as harsh environment. Still I sand Gel coat almost all down.
 
Name it

You apply epoxy primer over the fiberglass and paint on top. ..

Please name a good epoxy primer and where to get.

I do not want to be putting down a primer and then the paint shop has an issue with it when i go to paint.
 
I recommend using the same system, which ever brand you use.

Sent you a PM for my brand of primer.

Phat
 
If i sand off the gel coat, do i need to apply epoxy and 410 over it or can i just primer/filler, sand, prime and paint?

Depends on how good you want it to look when done.

In general, working from bare epoxy/glass outward...

1. Contour - Goal is to set the shape of the part. This is where we use a bulk filler like dry micro, i.e. epoxy and microballoons mixed to something like firm peanut butter. As a rule, apply what seems like too much micro, rasp off the excess when it cures to the cheese state, then sand to contour after cure. The idea here is to apply micro one time. It's a common rookie mistake to apply, sand, find a low spot, apply more, sand, repeat. It doesn't work well because the multiple applications rarely contain the same ratio of epoxy to balloons. The sanding density is different, so the surface won't sand out level. One fat application guarantees consistent density, so it block sands level.

2. Seal - Both the epoxy/fabric and the cured/sanded filler will evidence pinholes and porosity, as well as 60 and 80 grit scratch marks. I prefer to seal with straight epoxy, wiped on with a squeegee, then rolled to eliminate drag marks. After cure, block sand with 120 or 180 grit. Which to use depends on the next step, 120 if subsequently spraying a primer/surfacer (see below), 180 if going directly to epoxy primer and topcoat. The later is mostly for small parts, like an intake snorkel.

3. Optically level - In the end, we want to be able to sight along large flat panels and not see any waves in the surface. Given low angle lighting, a wavy surface is ugly. To ensure a level surface, we spray a primer/surfacer, in essence a urethane primer containing a fillers like talc and styrene. It builds surface thickness, which is then block sanded for flatness. Block sanding is just what it sounds like, sandpaper on a hard (or quite firm) block...no sandpaper held in the bare hand. The goal is to cut the high spots while bridging across the lows. We're talking a few thousandths here. Contouring was back in step one.

Product lines vary in application details. For PPG, spray DPLF epoxy primer, the follow in 30 minutes with two cross coats of K36. Use a dark primer under the light primer surfacer, for contrast. When cured, block sand wet with 320 or 400. Work evenly with large strokes and the largest block suitable for the panel shape. When you see dark primer showing through the high spots, stop sanding, dry, wipe clean, and spray two more cross coats. Repeat the spray and blocking process as needed until sighting along the surface with low angle light shows no waves at all.

Blocking is an art form at the best shops. Here's a great example, Monty Barrett's 40 Ford. No waves in those body panels. Check the reflection in the left rear quarter.
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Monty's%2040%201000w.jpg


Monty's%20LRQ.jpg
 
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Roller

...
2. Seal - Both the epoxy/fabric and the cured/sanded filler will evidence pinholes and porosity, as well as 60 and 80 grit scratch marks. I prefer to seal with straight epoxy, wiped on with a squeegee, then rolled to eliminate drag marks. After cure, block sand with 120 or 180 grit. Which to use depends on the next step, 120 if subsequently spraying a primer/surfacer (see below), 180 if going directly to epoxy primer and topcoat. The later is mostly for small parts, like an intake snorkel.
...

Dan
When you mention "rolled to eliminate drag marks", do youbroll with a dry sponge roller?
 
Dan
When you mention "rolled to eliminate drag marks", do you roll with a dry sponge roller?

Dry or wet sponge roller, either works. I've used nappy rollers too, but someone reported fuzz in the cured surface. Hadn't happened to me, but sure enough, next batch of rollers I bought...
 
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