fiberglass prep

[erich weaver]

I want to fly before painting but it would seem prudent to protect and prepare the fiberglass parts in the meantime. Im a bit overwhelmed by the choices of products and techniques that seem to have been used. Is it acceptable to simply use a primer (PPG K38? Smooth Prime?) to both fill pinholes and prime and leave it at that? Just trying to keep it simple here, not re-ignite a primer war. I noticed on Checkoway's website that he used Smooth Prime on the cowl, but then a separate primer over that. Why - just a color thing?

thanks

E

[tcrv7]

I went to Sam James forum at OSH. What a great guy. He is fiberglass. Go to his website and get his 2hr video that is good as gold.

[Dave Fogarty]

Originally Posted by tcrv7

I went to Sam James forum at OSH. What a great guy. He is fiberglass. Go to his website and get his 2hr video that is good as gold.

Hi Tom -

I'm an RV newbie - can you give us a link to this fellow's website for the fiberglass video?

I have used polyester glass for my model airplanes (because it sands so well and is compatible with lots of other materials). Do you know what type of glass the Van's folks use? I would assume it is epoxy glass, but I'm new to this game so I'll take all the advise I can get !

Thanks for the posts & all the best.

[tcrv7]

google james aircraft or sam james cowl Idont know how to add a link. Istill type with one finger and do the swirling finger thing to find the letter i want good luck.

[Norman CYYJ]

The cowling, gear leg and wheel pants are epoxy. You should use epoxy on these parts it is not compatible with polyester resins. You will have to sand and fill all the pin holes before priming. Hours of work and millions of pins holes to fill still after you think you are done. If you fly first and the holes are not filled you run the risk of grease and dirt getting into the holes which will cause you nothing but grief when it come time to paint. Have fun and be thankful that you are not building a glass plane.

[mandm1516]

JamesAircraft.com

Mike

[Kyle Boatright]

I used UV smoothprime on my airplane and was happy with the results. However, there are a number of people in the Canard community who have seen bubbling under the Smooth Prime. That eventually led to paint failures.

Historically, filler primers (other than smoothprime) have not been considered to be very effective against pinholes. They tend to bridge the holes, then as soon as you do a little sanding, you sand away the bridge and the pinhole is back.

Recently, it seems that the favored technique is to squeegie a couple of coats of raw epoxy into the fiberglass parts to fill the pinholes. A similar technique is to sqeegie SuperFil into the pinholes. Using either technique, you'll need to apply a coat, sand, apply another coat, etc.

The final test is if you can apply a thin layer of primer at the end and no pinholes appear.

[RWoodard]

I'd suggest that prep your fiberglass as much as you can--as if you were going to paint tomorrow.

Sand a bunch. Sand until you think you're ready for paint with no pin holes or imperfections. Then spray some sandable filler-primer. You'll be amazed how the imperfections show up. At this point you'll probably want to use some filler before you sand some more. I've been using some stuff called Superfil from Aircraft Spruce. I used this based on advice from a guy who built a VERY nice Lancair.

After you've filled all the little pinholes and imperfections with Superfil, sanded again with ~320--400 grit sandpaper, then prime again. Repeat the process until you see no more imperfections. When you see no more imperfections, spray one more coat of primer and leave it alone until you're ready to paint.

As for filler/primer, I'd suggest an Evercoat brand product called Uro Fill.

Another little thing I learned from hanging out at my brother-in-law's body shop is how cool "Guide Coat" is for sanding fiberglass. All guide coat is is a light splattered dusting of a contrasting spray paint on the grey-primed fiberglass part. As you sand, the splattered dots of the guide coat make it very obvious where the high and low spots are in the fiberglass. SEM makes an actual guide coat product, but I would think just a spritzing with a contrasting primer color from any old rattle can would work, too. I wouldn't use a regular paint because I think it would be too thick and might not sand as well.

It's amazing all the little tricks the paint shop guys have to make this stuff look good!

Best regards,

Rod Woodard
Loveland, Colorado (KFNL)
Midget Mustang @ the paint shop
RV-8 #81964 holding at the wings

[DanH]

I've been experimenting with squeegee coats of epoxy as the first step in final finishing, and I'm sold.

[az_gila]

Originally Posted by RWoodard

.......

Another little thing I learned from hanging out at my brother-in-law's body shop is how cool "Guide Coat" is for sanding fiberglass. All guide coat is is a light splattered dusting of a contrasting spray paint on the grey-primed fiberglass part. As you sand, the splattered dots of the guide coat make it very obvious where the high and low spots are in the fiberglass.
......
Rod Woodard

Rob.... when I was re-finishing my fiberglass sailplane, a professional give me this tip for guide coats...

Mix 10% blue lacquer paint and 90% lacquer thinner. This gives a real thin colored paint.
After each sanding session, just wipe the mixture over the area you worked on... it dries almost instantly... and that is your guide coat for the next sanding session.

The advantage of this method is instant drying, no equipment needed, just a cloth wipe, and the "paint" is so thin it wicks into very scratch and highlights them.
Now just sand until all of the blue scratches disappear... ...then move on to the next higher grit and repeat...

Try it...

gil in Tucson