Primer over gelcoat?
- Thread starter m511y
- Start date
rockcitycafe
I make things.
that part is from a brand new mold, so the surface is really high gloss, I'd hit it with some 400 grit just to make sure the paint has a good surface to grab, I don't recommend shooting paint straight onto gelcoat, I've always felt that a good primer will eat a bit at the gelcoat and provide a really nice surface for the paint
rockcitycafe
I make things.
I've had good luck with it, the trick with primer is to make sure you let it dry for a good few days imo, sometimes it doesn't fully dry and the whole paint layer never fully hardens
axeugene27
Over 1,000 Posts
see sometimes you can directly talk to the manufacturer and get good answers. One of the benifits of buying small company american made stuff.
Booligan
Been Around the Block
BTW, how do you like the Bonneville seat? I was looking at it for my CB175 buildup, but wasn't sure about the width of the flat portion of the seat. The 175 has a funky spot where I would be mounting it up, and the width of the flat mounting area is important. Looks like their site says that it's 7.5" wide, but with the sloped sides of the seating area, I'm not sure what I'd be working with.
HollywoodMX
Coast to Coast
Red Devil said:
I sanded mine with 400 as 500 was taking its time to get the shiney part of the gel coat.
But the 400 has left visible scratches so I was thinking either sand to 600 (I'm going black) or filler primer as ism then paint. I'm thinking 600 sanding is my best bet (less work) then priming and sanding for base, BUT if primer will make a better finish I will do it.
mathil
Been Around the Block
I see this thread got raised from the dead, but for future reference...
Fiberglass molds have intentional contaminants added to their surface. These come in the form of waxes, mold releases and PVA. All of these things are anathema to a good paint job.
It is possible to paint basecoat directly on gelcoat. I've done it probably 100 times, but first you need to be absolutely sure all the release products are off of it. You need to remove these before sanding, or you'll only succeed in sanding them into the surface. Basecoats are sensitive to such contaminants and will puddle, or fisheye, or generate other flaws if you're lazy on the prep.
Before you sand it wash it with TSP, wax and grease remover, soapy water, acetone and rubbing alcohol. It sounds excessive, but you have to use a solvent that can remove the mold release. Basically, wash it with everything in your arsenal before you paint.
Sanding to 400 grit is sufficient for a basecoat. Make sure you sand until there is absolutely no shine left on the part in any small patches. I prefer to sand to 400, spray sealer and then spray base wet on that. The reason is if you have a white gelcoat seat and you're painting it red you'd have to put an excessive amount of basecoat on it to achieve hiding, as opposed to a black sealer. Every basecoat color has an ideal substrate color of black, gray or white. Metallic red over white has been the hardest to achieve hiding in my experience.
Fiberglass molds have intentional contaminants added to their surface. These come in the form of waxes, mold releases and PVA. All of these things are anathema to a good paint job.
It is possible to paint basecoat directly on gelcoat. I've done it probably 100 times, but first you need to be absolutely sure all the release products are off of it. You need to remove these before sanding, or you'll only succeed in sanding them into the surface. Basecoats are sensitive to such contaminants and will puddle, or fisheye, or generate other flaws if you're lazy on the prep.
Before you sand it wash it with TSP, wax and grease remover, soapy water, acetone and rubbing alcohol. It sounds excessive, but you have to use a solvent that can remove the mold release. Basically, wash it with everything in your arsenal before you paint.
Sanding to 400 grit is sufficient for a basecoat. Make sure you sand until there is absolutely no shine left on the part in any small patches. I prefer to sand to 400, spray sealer and then spray base wet on that. The reason is if you have a white gelcoat seat and you're painting it red you'd have to put an excessive amount of basecoat on it to achieve hiding, as opposed to a black sealer. Every basecoat color has an ideal substrate color of black, gray or white. Metallic red over white has been the hardest to achieve hiding in my experience.
HollywoodMX
Coast to Coast
mathil said:
Funny thing I have all those cleaning agents you mentioned. I never thought of using TSP though ever on motorcycles.
I have sealer and primer. Curious, Why use sealer over using primer?
mathil
Been Around the Block
Primer and sealer are 2 different products for 2 different things.
Primer is (usually) a high build product, which is expected to be block sanded to achieve flatness. Some have mixing instructions for reducers to make them spray flatter. It's thicker and more porous than sealer.
Sealer is thinner, is designed to spray flat and level out, and more importantly is designed for a wet on wet application of basecoat where primer usually isn't. It's meant to seal and provide an even finish on various exposed substrates, so no variances show through and affect the basecoat coloration. Metallics especially will lay down differently on primer, sealer, filler and gelcoat.
Different products for different situations. If I was spraying red metallic on black gelcoat I would just sand the gel to 400 and spray the base. If it was a white gel seat I would sand 400, spray a black sealer and then spray the red metallic wet on wet on the sealer. If I had to do bodywork to a fiberglass part I'd do my filler work, prime the worked area, block the primer, spray a coat of sealer and spray the base wet.
For instance for my business I lengthen a fiberglass poptop by adding a section in. The part is 10'x5', but my bodywork is just a 10" strip in the middle. I do my glass work, do my filler work, and prime over the bondo. I sand that primer, feather it in, and sand the whole thing to 400. I could spray base right away, it would definitely stick. However, a coat of sealer gives an even surface for metallics (vs primer and gel), an even color (as opposed to white gel and gray primer), and let's me tailor the sealer color to work with the base. The sealer only adds 15 minutes to the process, as I spray base on it while it's still wet, and don't have to sand it. It saves on basecoat, since you don't have to lay down a ton of base trying to achieve hide. Pros in that situation far outweigh the cons.
On an offshoot, I used my new gun for the first time today. Devilbiss Tekna Prolite. Moving to a real gun over a lower priced gun, or a harbor freight special is an AMAZING difference.
Primer is (usually) a high build product, which is expected to be block sanded to achieve flatness. Some have mixing instructions for reducers to make them spray flatter. It's thicker and more porous than sealer.
Sealer is thinner, is designed to spray flat and level out, and more importantly is designed for a wet on wet application of basecoat where primer usually isn't. It's meant to seal and provide an even finish on various exposed substrates, so no variances show through and affect the basecoat coloration. Metallics especially will lay down differently on primer, sealer, filler and gelcoat.
Different products for different situations. If I was spraying red metallic on black gelcoat I would just sand the gel to 400 and spray the base. If it was a white gel seat I would sand 400, spray a black sealer and then spray the red metallic wet on wet on the sealer. If I had to do bodywork to a fiberglass part I'd do my filler work, prime the worked area, block the primer, spray a coat of sealer and spray the base wet.
For instance for my business I lengthen a fiberglass poptop by adding a section in. The part is 10'x5', but my bodywork is just a 10" strip in the middle. I do my glass work, do my filler work, and prime over the bondo. I sand that primer, feather it in, and sand the whole thing to 400. I could spray base right away, it would definitely stick. However, a coat of sealer gives an even surface for metallics (vs primer and gel), an even color (as opposed to white gel and gray primer), and let's me tailor the sealer color to work with the base. The sealer only adds 15 minutes to the process, as I spray base on it while it's still wet, and don't have to sand it. It saves on basecoat, since you don't have to lay down a ton of base trying to achieve hide. Pros in that situation far outweigh the cons.
On an offshoot, I used my new gun for the first time today. Devilbiss Tekna Prolite. Moving to a real gun over a lower priced gun, or a harbor freight special is an AMAZING difference.
HollywoodMX
Coast to Coast
Ya I will start using the tsp before wax and grease remover.
So this is my situation, I have white gel coat seat, and metal tank with bondo work. Final paint is a (single stage) black urethane enamel, base, thinner, hardener. Gun is a Iwata lph80-124g w/pps integration.
I was going to prime the tank with etching primer. I want the tank and seat to have uniform paint and finish, so it doesn't seem I can just use the sealer on the seat and then primer on the tank. I do like the idea of painting over the wet sealer but I worry about that. Paints are very specific and I don't want to alter the chemical properties of the two paints mixing especially wet unless its the approved/specified sealer from the same paint line.
So this is my situation, I have white gel coat seat, and metal tank with bondo work. Final paint is a (single stage) black urethane enamel, base, thinner, hardener. Gun is a Iwata lph80-124g w/pps integration.
I was going to prime the tank with etching primer. I want the tank and seat to have uniform paint and finish, so it doesn't seem I can just use the sealer on the seat and then primer on the tank. I do like the idea of painting over the wet sealer but I worry about that. Paints are very specific and I don't want to alter the chemical properties of the two paints mixing especially wet unless its the approved/specified sealer from the same paint line.
High On Octane
Ton Up or Shut Up
Your best and most cost effective solution is to use a 2K urethane primer. It will have excellent adhesion to many surfaces including bare metal, plastic and fiberglass. I like to mix my 2K primer 4:1:2 and use as I sealer too, it works very well. If all of your body work is done and your surface is sanded to 320 grit or finer, just use the 2K as 4:1:2 sealer, 2 coats waiting 10-15 minutes in between coats (or until completely flashed off) and wait about 20 minutes and you can top coat with the urethane enamel right on top.
Scottie J
Scottie J
HollywoodMX
Coast to Coast
High On Octane said:
Ya i had good results with 2k primer before. Seems to go on quite smooth compared to regular primer. Only ready I was avoiding it was to minimize my exposure to the iso's.
*edited some bad cell phone typos.
High On Octane
Ton Up or Shut Up
I've been painting for 10 years so imagine all the VOCs I've been exposed to. If you're painting in your garage put a box fan in a window or doorway to keep the air circulating.
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