[Craig legacy]

I'm finishing up the bodywork on my 59 Chevy Apache Fleetside bed. I've already completed the front end. On the front I used Mar-Hyde Single Stage Etching Primer to the bare metal, which included some repaired areas with filler. I then used a high build polyester primer.

Now that I'm on the bed I smoothed the tailgate and it has a skim coat of filler. Should I use the polyester primer over it, or is it ok to first use the etching primer because there is a small amount of exposed metal. It was media blasted before I started the bodywork. I'm concerned that the etching primer is bad for filler.

The etching primer can says its ok to use under all primer surfaces.

Thanks for the help.

[kenseth17]

Many etch primers have strict warning against using body fillers over or under etch primer. Polyester and the acid in etch primers generally don't mix. I would assume the same would hold true with polyester primer. Although I believe Martinsr had said some manufacturers say its okay, generally its not the case when you look at tech sheets. Thats why many people like epoxy primer and avoid etch. It is compatable with so much more, and also is a 2k product which will not be attacked by solvent, and when cured will provide excellent protection of the substrate from air and moisture. self etch is a 1k and doesn't provide these kind of benefits. I would think you would want to epoxy over the etch before using any bodyfillers or polyester based primer. I don't know what to say at this point. No idea what everything looks like underneath.

[Craig legacy]

Thanks for your input. I have done some research and the Mar-Hyde etching primer and it states that it is compateble with all types of primer. In fact the PCL polyester primer I used states that for the best adhesion use it over an etching primer.

I'm still concerned about the etching primer over the filler. I checked out the website bondo.com for the Mar-hyde product but could not get a tech sheet.
I talked to the place that sold me the product and he said it would be ok. I would feel better if I could get a tech sheet on the product.

For the bed, I will just use the etching primer on exposed metal and stay away from filler areas. As for the front end I'm thinking about taking off the coat of polyester primer to get down to the filler areas, and then re-shoot it before I block sand.

What do you guys think?

Thanks

[kenseth17]

Well here are my opinions. If someone has a different one, they'll have to state theirs. I don't see any reason to really use acid etch over your exposed metal areas. Polyester primer is basically sprayable body filler, and for years everyone applied this over baremetal. Etch primer only benefits is etching the surface and getting rid of flash rust that may have occurred. If the metal has been exposed to moisture in the air for a good period of time, simply sand it to remove and then apply more poly primer. As long is the metal is clean and sanded for mechanical adhesion, the polyprimer should be fine. The best still would be epoxy and then your fill primer, epoxy is the only primer when cured that will totally seal against air and moisture, which makes it good for corrosion protection when used properly. If you must acid etch, I believe that most generally say hit your baremetal area, and okay to go a little on to the filler area, but don't apply over the whole bodyfiller area, just your baremetal spots. You should never paint over etching primer, another primer should be used over it first. I really rarely have used acid etch, never really did even back in the days they recommended acid etch or metal conditioner followed by an epoxy. I always seen it as an unneccessary step of you do a proper job sanding or removng rust, and judged it to more problems then benefits I guess, not worth the extra expense, except in some situations where corrosion and you just cannot get into blast or clean properly. Thats what I'd reserve the phosphoric acid-conversion products for. Alot of places I've worked that fabricated aluminum parts seemed to like acid etching or washing followed by urethane primer though.

[Craig legacy]

It is amazing on all the different thought processes about primer. I never thought primer would be this confusing. I have had the metal media blasted, and then sanded, filled. I will follow your recommendations and just use the poly primer as the metal is clean.

Thank you for all your help. This site rocks!