I have heard plenty of good things about the use of etching primers. And I recently finished a patch panel on a fender and wanted to coat it while I start prep on the rest of the car so I bought an etching primer. But after reading all the directions on the primer it says that I can paint the fender with it but should not leave it in the etching primer alone for longer than about a week before applying a coat of regular primer followed by a basecoat. I thought that etching primer WAS primer and that was that. Am I understanding this correctly or can I leave the fender in the etching primer or even paint over the top of it with no buffer coat of some sort?
This is true, as you need to seal the etching primer. If you dont the etching primer will stain the paint also. Just so you know, Slick sand can NOT be shot over the etching primer. It will not dry corectly, somthing to do with the make up of slick sand. Use a brand that is compatable to the brand of etching primer. Etching primer is just a rust preventor, not a primer, it had no building properties. Good Luck. BISHOP.
Primer is not just primer. There are different types of primer, etching is just one type. The 3 main types are adhesion primer, which is made to stick very well to the substrate, and allow further coats of paint to stick to it, surfacer primer, which is made with lots of solids, to fill scratches and minor imperfections, and last, sealer primer, made to form a barrier between what's under the paint and the paint. This can mean body filler, the activator for the filler (which can bleach up into the paint), or any old paint. Pretty much none of the primers are made to be a topcoat, to last a long time on it's own, either. Etch primer is an adhesion primer, made to esp. stick to bare metal. but will degrade quickly unless coated with something else. Primers can be one, two, or all three of the above types.
To continue what chopolds said here is what a good friend and paint rep for PPG taught me. I am sure the info pertains to other paint manufacturers - but it is always good to call or otherwise contact the paint company's tech line for their specific recommendations. Meanwhile this is the deal: Etch prime has acid in it. It is how it "Etches" It is a really good ground coat (right over bare metal) usually. Because of the acid, it is not a good coating to add fillers to and use as a primer surfacer - why? the acid likes to leach into topcoat color and stain it. Use etch prime as a corrosion inhibitor and then put a good couple of coats of primer surfacer over it before you start any stick or block sanding. Epoxy primers have plasticizer in them and act as adhesion promoters - make whatever is put on next stick better, including plastic filler. I have seen lab tests that show plastic filler sticking 40% to 50% better when spread over an area coated with PPG DP epoxy prime. Anyway - it is not a filler primer either. Remember - none of these products have UV screener in them. They are primers - intended to be covered by another primer or topcoat system, not left to the elements. Yes, primers will usually absorb water - the surfacers especially. Some even get case hardened - PPG K-36 and K-38 will case harden when wet sanded decreasing it's adhesion characteristics and causing topcoat adhesion problems later. No problem, just dry sand it before the next step. If you like the suede look and don't want to keep priming the car over and over to keep it fresh, use a topcoat color with flattening agent in it.
My process is sand, epoxy primer, filler, filler primer, thinned epoxy primer as sealer, topcoat, clearcoat. I choose not to use etch because of the acid and all the other incidentals you have to remember about interactions with etch primer due to acid. NOTE that you canNOT use etch primer if you use rust inhibitor, so for a simple minded guy like me, it's just easier to only use epoxy.
Right on.... I'm with you. Not much on spraying acid etch stuff - two part urethanes are enough iso stuff to have floating around. My procedure is a lot like yours.
so what your saying is that i can put epoxy primer over bare metal. if so, what grit sandpapaer do you use on the bare metal. just need to know for my own good.what brand paint/primer do you recommend for a rookie?
I (and Chopolds) use HOK epoxy primers. They are a bit more expensive but are definitely worth it. Over bare metal, I use HOK's Direct to Metal KD2000. Not a filler primer, but adheres like all hell. Bare metal must be sanded with 40 grit before priming. Then I add my filler, then HOK's KP2CF Epoxy primer (which will fill when not reduced), then block woith a guide coat, then HOK's KO-Seal II for a sealer, then my basecoat/topcoat. Never had a probelm and Mark (Chopolds) has never had a problem for even longer! The best custom primer system IMO.
Its all good advise on here, just remember one thing though, never epoxy prime over any acid etch primers, it will peel in sheets, but if the etch is already down you can urethane prime over it, etch was originally designed to be applied over unsanded metals, the acid makes it stick rather than the sanded, roughed up surface, I use valspar epoxy or there direct to metal primers, and have used them over unsanded aluminum and steel, tough as hell, well they own house of kolor now so it all adds up, its good stuff
There are basically 2 kinds of etch primer. Vinyl wash primer: very little build (fill) and it is slightly more aggressive, acid wise because it has only a vinyl resin as the film. This etch primer should be coated with either a primer sealer or primer surfacer (filling primer) before a topcoat/paint is applied usually with a wet on wet system after the etch primer has flashed for 1/2 to 2 hours. In industrial/fleet applications this is usually applied to sandblasted steel or aluminum then sealed with a primer sealer and painted. For restorations it is usually applied to bare sandblasted steel or aluminum and primed with a filler primer so it can be blocked sanded or leveled before painting. This type of etch primer should not be used over body filler. Mild etching primer: this has some build or fill but is less agressive acidwise because of the solids or filler in the primer. This can be painted over with some single stage paints without other primers (check the tech info for the brand). It is usually applied to sandblasted steel or aluminum and can be coated with primer surfacer (filling primer) or sealer wet on wet after about 30 minutes up to 72 hours (or longer) with some brands. This type of etch primer is OK over body filler. Most companies use the same activator/reducer for both etch primers, which is a solvent blend with about 5% phosphoric acid. Automotive panels new from the factory have a phosphate coating on the bare steel. When you sandblast or sand the metal on a car you usually remove all or some of this coating. You can replace this factory corrosion protection (phosphating) with a 2 part metal prep acid wash which is messy and time consuming. Although not quite as good, using an etch primer on old sandblasted or sanded steel panels is the closest you can get to replacing the phosphate coating. If you use the metal prep and converting system to phosphate coat panels, you should NOT use an etch primer. Several automotive refinish companies require using an etch primer when repairing new car finishes in order for the paint and repair to be warrantied at the bodyshop. Polyester based primers (featherfill-morton eliminator-etc) usually cannot be applied over etch primers, because the acid will slow down the catalyst (MEKP) in the polyester primer and cause the cure to be longer. I did read in the new Evercoat Easy Sand tech sheet, for that brand of polyester primer surfacer, it can be applied over etch primer but it extends the cure time of the primer. AS always, read the tech info. Most of these companies have good information available on the web or at their local distributor's store, and you can always email or 1-800 a question to their tech dept. As with all good priming systems (epoxy-etch-urethane-polyester-etc) , if you read the tech info,it always says: "The bare steel should be clean of grease, oil, and dirt and free from rust." overspray
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