panels are straight at this point? then hit them with 220 to give tooth to the high build

220 is good.Just don`t sand it too much to the point that you sand through it.It just needs to be scuffed enough for the high build to have a good bite.

even though the high build says it is good on bare metal.....it is not. make sure there is some sort of epoxy primer or a two part etching primer over the bare metal before applying high build. The bare metal that the high build is referring to is a small cut through on an edge or a slight burn through the size of a match stick or less, applying over any larger an area and it will chip off and rust. The epoxy primer (and also etching primer) provides a layer of corrosion resistance and bites into the metal for long lasting results. I have seen far too many cars come through my shop that have been primed with high build because it said so on the can, we have had to strip them back down to metal and start again everytime because the primer would peel even during sanding.

^^^^ Awesome read to share, link is from:
www.gearheaddiva.com/5397/epoxy-vs-self-etching-primer-for-painting-bare-metal/

Epoxy vs. Self-Etching Primer for Painting Bare Metal



Visit any automotive forum and you cant help but stumble upon a long running debate on which direct to metal product is better, etch primer or epoxy primer. You will hear all kinds of technical facts, personal experiences as well as flat out unsubstantiated opinion. Then throw in the thousands of products available for the job, each with their own recommendations, and youll find yourself overwhelmed.

But after the smoke finally clears the fact remains that both types of primers will give you successful results if used correctly. The route you choose depends on the condition of the metal youre starting with, the time you have to devote to the bodywork and paint process, your budget and a bit of personal preference. Above all else, once you decide on your color, use that companys paint products from the bare metal stage to the final topcoat. Mixing products to save a few bucks will most likely cause adhesion problems no matter which bare metal primer you choose.

Self-Etching Primer

An etching primer uses an acid to chemically clean and micro-etch the metal surface for a better mechanical bite to promote adhesion with the layer of high-build primer to follow while also providing a layer of corrosion resistance on the metal. Because it cures quickly, its the method of choice for collision shops. But a key difference with etch primer is that you need to apply your filler or bondo first directly to the metal before spraying it. An example of the application order on bare metal is: 1) bodywork including filler/bondo 2) paint prep solvent 3) self-etch primer 4) high-build primer 5) basecoat 6) clearcoat.

Recommendations

If your metal surface is mostly smooth, you dont have areas with rust problems and you dont plan on having to use additional filler or bondo, then self-etch is a great option. Any slight imperfections and small sanding scratches will be filled with high-build primer in the next step. Its also useful for painting small parts or body panels with hard-to-reach areas that you cant scuff easily with sandpaper or a pad. Self-etching primer will get in there and bite into metal for you.

Heres an example of self-etching primer sprayed over panels with only some minor bodywork done. Youll notice differences in color as it dries over bare metal versus body filler. This 67 convertible Chevelle at Martin Automotive was etched with 2 parts PE995 Corrosion Shield Etching Primer and 3 parts ER997 Corrosion Shield Reducer by Sherwin-Williams.



Unless you only have a few minor issues to fix, its challenging for us do-it-yourselfers to carve out enough time to strip the old paint to bare metal, do the repairs, apply bondo and then spray a layer of self-etching primer before surface rust begins to form on the body. In this case, a more realistic option may be to use an epoxy primer.

Epoxy Primer

As the name implies, epoxy primer gives you excellent adhesion, similar to applying epoxy glue while also sealing the bare metal from environmental elements. Since it relies on forming a mechanical bond with the metal, you have to manually create the bite it needs by sanding the entire surface of the body with 80 to 180-grit sandpaper. Once the epoxy primer is down you no longer have to worry about rust while doing your repairs especially since you can apply body filler right on top of it. Then simply respray the areas you worked on to re-seal them. Although it takes longer to cure than self-etch primer, restoration shops tend to favor epoxy primers because of they often handle more extensive body repair projects. An example of the application order on bare metal is: 1) paint prep solvent 2) epoxy primer 3) bodywork including filler/bondo 4) epoxy primer on repair areas or over entire car again 5) high-build primer 6) basecoat 7) clearcoat.

Recommendations

If your bare metal body is going to need some work or your going for a flawless finish, then youre better off using epoxy primer because it gives you a layer that can be sanded and filled as needed. Pay attention to your products recoat window. During the recoat window (usually a few days) you can add filler and another coat of epoxy primer without first having to scuff the surface. If you let your project sit for a week or more, then youll have to sand (scuff) the original layer before you pickup where you left off. That does introduce an extra step for weekend warriors but its a small price to pay for being able to work at your own pace and not have to worry about rust.

 

-- Edited by Beaumont67SD on Tuesday 7th of October 2014 07:32:52 AM