The Stovebolt Site Forums The Shop Area Paint and Body Shop Painting over a sandblasted area??

To achieve the best final results what is the proper procedure for painting a sandblasted fender..?

do you have to sand the panel back smooth or or is it better to leave it abrasive for better adhesion?

I am sorry if this is a repeat post, I have searched off and on for four days and I cant find what I am looking for. Any help is appreciated.

I just prime it.

rattle can?

I don't think you will get a good end result by starting with a rattle can. A good paintjob will require some equipment.

Mike

mind you I am asking because I have no paint experience but whats the difference between rattle can primer and paint gun primer....I am pretty awesome with a rattle can, I have no problems getting an amazingly even and professional looking job down...is it the quality of the primer or something?

What kind of equipment? I have a compressor so a spray gun? or more than that?

Fresh, clean metal deserves epoxy primer. It will not allow rust through and will take overcoats well (if properly prepped). People have reported finding epoxy primer in rattle-cans but none have reported back after using it.

Whatever you use, make sure it is compatible with whatever other sealers, primers, surfacers, etc and finish coats that you will be using (use products within the same "paint system" to be safest).

I don't think I have any intentions of painting my own truck but i will need to prime my sandblasted areas as I go so they do not re-rust before I bring the entire truck to the body shop for paint...best way to do this?

Silverado,
Go with what TCLederman recommends and stay with the same paint system through out. One product does not always perform well with another.

In that case, find out what system the body shop uses and choose an epoxy primer in that system. Or, ask the shop what THEY recommend (so that what you do is compatible with their system).

good plan...
just so I am clear though, it is not necessary to sand smooth the panels after sandblasting them though correct?

that's correct, good sandblasting leaves the surface with good "tooth" for initial sealing primer - and as said, epoxy primer is the correct thing to use

Bill

great, thanks guys!

Silverado,
I use a cleaning solvent designed for removing all dirt and other stuff from the metal, then apply a couple coats of a urathane or epoxy primer,(urathane is less expensive) and wet sand with a 600/800 grit. Both will act as a filler for very light scratches.Sounds and is alot of work, but remember if the primer coats are not done right, the problems will follow all the way thru. Good luck.

Mike

what is the name of the solvent?

Since you said in preporation for final paint then just painting for a temporary rust prevention is not the plan I take it? If so then what you will need is the smoothest metal you can get before you put any primer on it and that will mean needing to know what it was blasted with and what is it's present condition. Until you know that I wouldn't worry about the type of paint to use. It could be several things.
Remember, you'll never see a body shop take a car directly from the blasting room to the paint room. It must be prepared first unless your looking for a homebrewed paint job that will stick out like a sore thumb. No paint job is ever going to be better than the preparation that was put into it. And it's true of your garage door as well as what's in the garage.

in hind sight my orignal post should have read :
I am slowly sandblasting parts of my truck for proper panel repair (filling) and modification (patches). After sandblasting I am concerned about re-rusting. What is the best way to prevent this from happening whilst not creating more work for the body shop that will be painting my truck in the end.

This is my action plan example:

Sandblast fender

hammer and dolly any large damaged areas

remove rusted sections and weld in patch panels (not necessary on my fenders)

apply filler and sand it smooth

primer entire fender (rust prevention only)

Should I orbital sand the entire fender smooth before spraying a protective coat? will the body shop sand my entire truck smooth before they do anything?

Epoxy Primer - and, be sure that the product you use is compatible with upper coat products that you or others will be later applying. Whatever products you use will (should) have product information sheets that explain what the product may be applied to and how to apply additional products on top.

There are (almost) no rattle can epoxy primers. Any other primers will let moisture through the primer and rust will eventually form on the metal.

It doesn't matter which Epoxy Primer or 2K primer you use. All top coat are compatible with them.

The route you should follow is:

Sandblast as many parts as you can.

Apply one coat of Epoxy Primer and let dry for approx 1 hour. Then apply two coats of 2K primer. Put parts away until you are ready to work any dents.

Epoxy Primer is hard to sand, however, if you apply 2 coats of 2K (which is easy to sand) you can work your dents through the 2K. You can then block sand with 320 wet to get a nice flat surface. Shoot another coat of 2K primer and block with 400 wet for solid colors or 600 for metallic color.

The epoxy primer will block any moisture from getting to the metal, the 2K will give you an easy surface to sand.

Frank Cox
Cox Custom Cars

Just a couple of thoughts on the matter- - - - - -when I ran a body shop, I would absolutely refuse to paint a vehicle with somebody else's prime job on it. The only exception to that rule would be if I removed all the primer to bare metal and started over. Primer is the base that all the rest of the paint job uses to hang onto the metal. Any mistake or application error will trash the paint job before you start.

Sandblasted sheet metal will have ripples in the grain structure of the metal that cannot be sanded smooth- - - -don't bother trying. Multiple layers of a high-build primer such as self-etching epoxy might cover up the ripples, but you'll need to prime, then sand, prime again, sand with a finer grit of paper, and prime and sand at least one more time. I would start with 180 grit, then 220, and maybe 320 before applying the color coat. Once you start priming, don't let the primer get exposed to weather- - - it's porous, and soaks up water like a sponge. If you drive a primed vehicle and it rains, the absorbed rainwater is trapped under the paint when you get around to applying the color coat. Eventually that moisture results in rust under the paint, or bubbles from poor adhesion of the color coat. Before applying the first coat of primer, spend a LOT of time with a high-pressure air hose, blowing as much of the sand residue off the metal as possible. A less aggressive blasting media such as glass beads or baking soda does a lot less damage to the metal. NEVER use sand on sheet metal.
Jerry

Jerry that's very good information until the part of NEVER use sand on sheet metal.Technique and sand size will prevent any damage.I would love to use glass beads or baking soda that would cost so much my projects would come to a stand still.When I remove paint from a aircraft we use the dry ice blaster not a cheap way but the customer can pay for it.

I've used sand on many rigs-soda/glass beads/walnut shells etc cost way too much for my small budget. A lot depends on the person blasting.