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What "primer" are you using on your fiberglass parts?

bertschb

bertschb

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What are folks using to touch up their fiberglass parts after working on them? I'm talking about spraying some kind of gray colored paint/primer so it matches the factory color. This would just be temporary until the final paint job. I just don't like the look of all the white areas where I've worked on the fairings, etc.
 
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Brian
Im b@lls deep in fiberglass work and using duplicolor auto primer filler/ fills deep scratches and sands easily. Primer grey in color.
Local auto parts store, I think Napa.
A
Early stages of emp fairing finish.
 

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If you mean paint primer...
I brush on a couple coats of 2K epoxy primer. Wet sand that flat. Spray two kr three coats of the same, but thinned for spraying. Wet sand that to 800. Ready for paint.
 
wirejock said:
If you mean paint primer...
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Unfortunately, I'm not sure what I mean. The fiberglass parts (fairings, etc) for the RV-14 come from the factory in gray. I don't know if that is paint or primer or colored gelcoat. No clue. As I've worked to fit the fiberglass parts I have areas with bare (white) fiberglass/flox/micro. I just want to hit those areas with something so it's the same color as the rest of the fiberglass as it came from the factory. Just looking for something quick to cover up the white spots until the airplane gets the real paint job by a professional when I'm done building.

I'm assuming the pro will sand down all the fiberglass parts and prepare the surface for paint as part of the painting process.
 
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I just used rattle can high build primer. The gray isn't an exact match for the factory gel coat, but close enough until I get in the paint shop. Making it pretty is nice, but the only practical reason to use anything at all is to protect it from U.V.
 
Is there any concern about the porosity of primer on exterior parts? Particularly on the cowling or other parts that could be exposed to oil, exhaust, or grime?
 
DanH said:
Brian, you can't go wrong with any good grade of 2-part epoxy primer.
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What would you recommend in gray? I already spent probably 100 hours researching primers when I started this build and landed on Akzo. I wanted gray but the Akzo primer we have available to us is green only. I don't really want to spend another 100 hours looking for a 2 part gray epoxy primer - especially if the finish painter is just going to sand it off.

Also- is it OK to just shoot the white spots and leave the areas I didn't disturb in the original finish from the factory or do I need to paint the entire article?
 
One suggestion is to prime the entire part with 2K epoxy primer after sanding the gelcoat with 180 grit to give the paint something to key into. The primer will highlight any faults in the surface and will also seal the part, being epoxy. When the time comes to prep for final painting the epoxy will be compatible with pretty well anything else that is applied over it.
I used two brands of industrial primer; Nason 2K ZP and the other is PPG EPOTEC. Both stick well and can be sanded nicely and cost about $80 for a gallon kit.
Otherwise if you just want to temporarily disguise the spots you could take the wing tip to an auto paint supplier and have them make up a matching rattle can of acrylic, which will stick to fiberglass, it doesn't need to be primer. In future the painters will sand it all back and prime it per their process.
 
I used PPG products on all of my fiberglass. K36 was the primer with K201 catalyst and DT870 reducer (the reducer was optional - it apparently increases pot life, so I used it). It was light grey in color and seemed to sand easy. And it was tough. I flew with the fiberglass unpainted (primer only) for almost 2-1/2 years with no issues. But it wasn't cheap. The pricing seemed to go WAY up post-pandemic, and the available sizes were very limited; I couldn't find pints of anything, only quarts and gallons.
 
bertschb said:
What would you recommend in gray?
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Can't go wrong with any of the major brands, so buy where the counter folks are friendly.

My personal go-to for high value projects is PPG Deltron DPLF, but I've been shooting the less pricy Shopline product on stuff like wheelpant repairs. Strikes me as a reasonable sand-off choice. https://max.ppg.com/adaptivemedia/rendition?id=9179d0e69a49041a16501b85e08112a28e898d54

SPI has a good rep, and they ship free: https://www.southernpolyurethanes.com/products/primers/epoxy-primer/

bertschb said:
Also- is it OK to just shoot the white spots and leave the areas I didn't disturb in the original finish from the factory or do I need to paint the entire article?
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There's no absolute yes/no answer. Sealing the bare work is a good idea, but forget about matching the gel coat color. If uniform color is high on your list, paint the whole part with a contrasting primer color, not the same gray as the underlying gel coat. Later, the contrast is a sanding guide.
 
Shoot whatever rattle can you can buy, but, maybe more important, did you protect the inside?
Maybe the 14 cowls come from the factory with something sprayed or coated inside.
 
wirejock said:
...but, maybe more important, did you protect the inside?
Maybe the 14 cowls come from the factory with something sprayed or coated inside.
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No. So far all I've done is add material (flox or micro) to the outside of the parts I've worked on. Haven't got to the cowlings yet.
 
Cowl gets hot and oil on inside. Other parts two part epoxy.

Rattle can might be OK, might not. It has to be compactable with top coat.

Most painters don't like going over someone else's primer for reasons, like adhesion and compatibility.

They will have to sand it off or seal it, which might cost more money. So use good primer.
 
I’ve used Evercoat slick sand on the outside with good results. Sands easily and available at the local automotive paint supply house.

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On the inside of the cowl I’ve used Petit EZ bilge paint (2 coats) on my last two builds. I use a brush on the first coat and high density foam roller on the second coat. Make sure you sand and clean thoroughly first.

 
I understand your confusion. Research is time consuming and then the decision is just made on school house data, no real experience. Here is another data point. There are 12 suggestions above. No one says you can screw this up. Its all encouraging. So get two dice, roll them go with their answer.
 
I’m a fan of the Akzo product line, specifically the Awlgrip 545 primer. This should be compatible with any topcoat, but certainly Awlgrip or Imron topcoats. A plus is availability at your local west marine if you’re in a coastal area. And they do recommend using 1K paints (Krylon, local auto parts store paints) for guide coats. I recommend rolling the first layer to help fill pinholes.
 
The grey factory color is actually a primer, the parts are primed in the mold before layup so there is a finish on it already. There is no "gel coat" for epoxy parts, a gel coat is used with polyester resin parts. Any 2K primer as mentioned above works fine with the factory finish.
 
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