Thanks guys, This isn't my post, but I think I learned something here, and that's what it's all about on the H.A.M.B. right?
I always start off with epoxy primer. Check the data sheets, sometimes you have to wait over an hour before putting a coat of something else over the epoxy. I used to use PPG DP primer, then DuPont's epoxy primer, and recently some Kirker epoxy primer that was a lot cheaper, but seemed to work well. Most of the fillers recommend not using them over self-etching primers because of the acid in the primer. But fillers stick really well to epoxy primer if you scuff it up a little. The corrosion resistance of good epoxy primers is about the best of any of the primers. You can check the data sheets from a lot of the paint companies online. If you want to compare them for corrosion resistance, check out how long they survive in a salt spray test.
If you want to compare them for corrosion resistance, check out how long they survive in a salt spray test.[/QUOTE] There's the key to the first info on what protection your primer will give you. When you read the tech info for salt spray tests look at the mil thickness of the primer film in the test and compare it to the dry film per coat of the product to see how many coats will give you that level of protection. Also make sure the salt spray tests are the same exposure/duration. Also compare the solids (lbs. per gallon) of the primers. Higher solids primers will give you more film build per coat, which if the resin that holds the solids together is good, will be a better corrosion protection primer. Film thickness is a huge part of the primer's ability to protect. A primer @3 1/2 lbs per gallon of solids is quite different than a primer @12 lbs per gallon of solids. That's like comparing a primer that is .5 mil per sprayable coat to one 1.5 mils per sprayable coat. If they are both similar in quality the higher build will give more corrosion protection if you apply 2 coats. You have to look at this information to see what is best for the job. It can also relate to cost. How much per sprayable film @ 3 mils will this cost. Maybe a little more cash will yield lots better protection. Now notice above I said "primer" not specifically epoxy or self etch or urethane or polyester. Do the above check on more than one primer that is reccommended for DTM (direct to metal), and read and follow the reccomended prep for bare metal application of each primer. There are a lot of really good primers and primer "systems" available. There's a lot of "I like epoxy (seems to roll of the tongue nicely) or whatever primer" for this or that application, but I'm betting that most primer afficianados have not read very deeply into many or any tech info to compare different products and see what really is best for the job. Every DTM primer and even body filler has this in the tech info: The bare metal must be clean and free from dirt, oil, and rust/corrosion. Sanding, blasting, grinding, solvents, detergents, and acids are the main ways of accomplishing the prep process before priming. If you start with properly prepared metal, use a good quality primer (in the recommended film thickness and application) and a good topcoat/paint, you should end up with a good finish that will last a long time. Notice again I said "PRIMER". The internet is full of free to look at tech sheets to help inform and make good choices. Do a little research and improve your skills and knowledge. overspray
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