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Priming wheel pants

Stockmanreef

Well Known Member
I am at the point where I should prime the wheel pants. Will primer stick well to the gel coat on the parts or does this have to be scuffed up prior to priming?

Thanks
 
Wash with water to make sure the release agent is all removed then sand with 320 or 400 then wax and grease remover and prime.
 
Priming should be done just before painting, so I only put primer on the areas where I applied Fiberglas - to protect the epoxy from UV. I left the rest of the gel coat intact for the paint shop to prime and paint.
 
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Priming should be done just before painting, so I only put primer on the areas where I applied Fiberglas - to protect the epoxy from UV. I left the rest of the gel coat intact for the paint shop to prime and paint. ��

Remember too that the outer grey layer on the newer fiberglass parts is just tinted epoxy and has no UV protection so if you are going to fly a while prior to painting, a coating of epoxy primer over all of the grey parts would be the best protection.
 
You should fill air the pinhole before primer. Search this site for methods, Dan Horton had a good post on that. Read your OP and noticed you have jel coated parts.You may not have any pinholes, count your blessings.
 
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You should fill air the pinhole before primer. Search this site for methods, Dan Horton had a good post on that. Read your OP and noticed you have jel coated parts.You may not have any pinholes, count your blessings.

There are definitely pinholes in the gel coated parts .. you can't really see them until you have sprayed primer then they start sticking out like sore thumbs :eek:
 
There are definitely pinholes in the gel coated parts .. you can't really see them until you have sprayed primer then they start sticking out like sore thumbs :eek:

+1

I was very disappointed in these parts. After sanding, the gelcoat had no pinholes. However, the gel coat was too thin. After spraying primer, 1000s of pinholes appeared, as the gel coat was too thin and broke down with the primers solvents.

Larry
 
"Gel coat" is typically used only in polyester layups and the wheel pants are epoxy. The grey coating on the outside is a layer of colored epoxy and most likely thickened to minimize pinholes. The colored epoxy layer is not a polyester "gel coat" even though people refer to it as such. Treat the grey layer as you would a non tinted part meaning it needs a protective coating (primer as a minimum) for any UV protection. You can always tell polyester by the smell.

Just to explain more, the pin holes you see are simply voids in the outer layer where it does not fill the cloth weave underneath. This can be from using an initial layer of cloth that has a coarse weave or an initial layer of glue not thickened enough to prevent the voids from showing. Either way, the glue doesn't fill the weave and you have a pin hole. Typically a layup would have a thickened coat of glue put down first and allowed to partially cure so it stays sticky but gooey enough to fill all of the voids in the first layer of fiberglass cloth to minimize pinholes. Of course a vacuum bag process if used should get all of the air out and then push the glue into every void preventing pin holes for the most part but not all parts are vacuum bagged when produced.
 
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The grey coating on the outside is a layer of colored epoxy and most likely thickened to minimize pinholes. .

You may be right, but I doubt it. I have sanded quite a bit of it and it sands just like gel coat and nothing like thickened epoxy.

Larry
 
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will "Filler Primer" take care of the pin holes?

Lots of ways to do this from drywall compound to high build primer to an auto body "icing" or "glazing" product or even traditional spot putty which all fill well with varying sanding difficulty and different degrees of strength and stability. I would put down a layer of epoxy primer first so that your finish is well adhered to the wheel pant before pin hole filling although most of these products can be applied right to the fiberglass. I like this Upol product that fills well and goes on like pancake batter and is reasonable to sand off.
https://www.amazon.com/U-Pol-Products-0670-LIQUID-Glazing/dp/B006N4EBWA

The key to pin hole filling is to sand the filler all the way off leaving only little dots in the pin holes. Depending on your method it may take several coats to completely fill the holes
 
Lots of ways to do this from drywall compound to high build primer to an auto body "icing" or "glazing" product or even traditional spot putty which all fill well with varying sanding difficulty and different degrees of strength and stability. I would put down a layer of epoxy primer first so that your finish is well adhered to the wheel pant before pin hole filling although most of these products can be applied right to the fiberglass. I like this Upol product that fills well and goes on like pancake batter and is reasonable to sand off.
https://www.amazon.com/U-Pol-Products-0670-LIQUID-Glazing/dp/B006N4EBWA

The key to pin hole filling is to sand the filler all the way off leaving only little dots in the pin holes. Depending on your method it may take several coats to completely fill the holes

Do not use spot putty or any non-catalyzed product. Otherwise it will trap solvents and you will get solvent pop. Looks like tiny pimples in the paint, the first time you take it in the sun.

Larry
 
One note, make sure you have all your holes drilled before priming. You may have to sand the gray down or off in places where you want to place a hole. To mark the location correctly I mounted a small led light inside (the nutplate), so it would shine outward through the epoxy to mark the spot. To do this you'll need to remove some of it so the light can come through. Also, like any surface before prime or paint, it needs to be lightly sanded or scotched to break the shiny surface, throughly cleaned with acetone, then go for it. At least that is what I did.
 
My assumption the outer layer was pigmented epoxy apparently was incorrect, thanks Scott for clarifying. The prime in the mold method does product a nice pin hole free surface just be aware that you are still relying on the inside layup to be pin hole free. Once you scuff to paint or sand vigorously to epoxy onto the part like fillets of cuffs you remove some or all of the thin primer layer and any underlying pin holes are exposed just like the older non primered parts. That said, the grey parts are much easier to finish than the old non primered parts which were simply riddled with pin holes.
 
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