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Purpose of a Primer and When should it be applied

First I'm giving you the situation,the truck has it's original 2008 Burgundy color on,it is just in a fair condition,roof and windshield area have rusted spots,the truck owner has decided to repair and do a complet paint job on it.
The new color will be a beige or so and he told me he won't be applying a primer on between the old paint and just go with the new color + an expensive clearcoat.
What should I warn him about,the color he chose will be altered (tint) if applied over that burgundy or not ,that's what I think.
What is the purpose of the primer,is the primer a protection or a layer needed for the base color to adhere or both of these situation.
Could you please give me a max of infos concerning the application of a primer.
So he is planning on shooting base over the rusted areas? The purpose of primer is to level an uneven surface, not repair rust. Any primer needs a clean surface to do it's job. No rust, grease, oil, tar, sap, or peeling paint. Anything other than proper preparation is a waste of time and money. The color he chose is the least of his problems. That being said, it is a good idea to at least spray a sealer before base to get an even tone under the base for coverage. A coat of epoxy sealer is cheaper than base, and will provide better adhesion and longevity.
Of course the rusted spots and areas will be repaired (rust cleaned off,bonded,decontaminated and primed),he just don't want to prime the entire truck to apply the base coat on but just the repaired areas.
Shooting a beige color on a burgundy original base with primed areas only isn't the best idea,the tint is looking at on his cardboard will not be the same as a final result,don't you think .
Not sure he will wash it before sanding it either,are you guys taking that extra time for this step or .
Concernig the sealer,does it need to be sanded too,do they come in differents types .
How many coats of Clear on a quad cab 2500 truck would you apply .

Thanks for getting back to me with your experience Texasking.


Trying to be the best me, I can be
Sounds like you guys are really new to all this so this is just the briefest of overviews. Use the search function on this site to learn more. Read through the SPI Tech Manual. It will help answer many of your questions. https://9beb57d8-8d44-4ec2-99ae-f7f...d/8ced3e_c0814bacc8a242e495a9d144b448cb14.pdf

If it's just a "repaint" on a older truck, then no, you don't need to prime the entire truck. Fix any problem areas, prime and sand those, and then sand the entire truck. Using a quality epoxy primer like SPI Epoxy on bare metal would be a good idea.
Washing the truck and wiping it down with a wax and grease remover like SPI 700 before sanding would be the "correct" thing to do. Not doing so you run the risk of sanding certain contaminants into the surface.
Sealer does not need to be sanded if applied correctly.
Two coats of clear would be considered the minimum. Most collision repair shops only do two coats. If you plan to do any sanding and buffing after clearing then three coats would be considered the minimum.
Once enough base is sprayed, the underlying color won't matter. The problem is the amount of base required to get full coverage. It may take 4-6 coats to cover a primer spot, and it is difficult to tell when it is covered without perfect lighting. One coat of sealer gives the base a uniform color to go over, therefore giving the illusion of complete coverage. Normally 2-3 coats is enough if the sealer has a similar shade as the base. On a color like he wants to spray, a medium gray would work. There are basically 2 types of sealer, urethane and epoxy. Neither requires sanding before base. Urethane is used more than epoxy because it is quicker drying, but epoxy is superior in many ways. Epoxy is a true sealer because it blocks solvent penetration. Epoxy also has superior adhesion properties, especially to metal. Epoxy will give much better chip resistance because of the adhesion properties. Washing the truck before sanding is not an extra step, it is required. Anything that is on the surface (oil, tar, wax, sap, etc.) will get "ground" into the paint when sanding, so it needs to be clean before sanding or it can cause lots of problems like fisheyes and poor adhesion. Most standard repaints get 2-3 coats of clear.
Not sure he will wash it before sanding it either,are you guys taking that extra time for this step or .

this is comin from a greenhorn so take it for what its worth.
i havent sprayed in a while but one thing for certain is i want the final result to be the best it can be with the knowledge i have. the very first thing i learned is dirt and dust WILL appear once the trigger is pulled on a spray gun IF the vehicle isnt properly and thoroughly washed. i made a 6" long wand for my pressure washer so i could get into wheel wells, undercarraige, engine bay, and any other area dust/dirt WILL hide. spray em dam good and from every angle possible. i take time and dont hit all them areas just once. after pressure washer, wash exterior with dawn dishsoap rinsing with just nozzle on hose and hit all them areas again with the hose.
seemed to work pretty darn good for me. what dust nibs i did get( which werent many) i think came from the paint booth- inna -shop, which when i set up that paint booth i spent a full day dusting out the shop before setting up the booth.

burgundy to beige???
Best advice i can give for any luck of it coming out ok & lasting a few years is wash & scrub it with Dawn before touching it with sandpaper. Water must not bead at all. One wet sheet of water u want. If you sand it without cleaning, all wax ect will get scored into surface. And use papertowels not towels and not the 1st few or last ones with glue on them.
I think this situation has been met so many times by the majority of you that after a few minutes talking with the owner you know if you're wasting your time trying to give him advices coming from pro and passionates DIY.
I wasted mine and don't want to waste yours but I thank you all for giving great infos,I will dig out more on Urethane and Epoxy Sealer,my 2014 RAM'roof needs attention before it goes too far.
I've sure apppreciated you guys taking time to shares your knowledges with me,this is a great forum.