Can self-etching primer be used as a general primer over body filler or old paint in addition to bare metal?
Member
Self Etching Primer Uses
Can self-etching primer be used as a general primer over body filler or old paint in addition to bare metal?
Body Shop Guru
Yes, it can.
but why would you? It has almost no film build. If you spray bare metal and get some on paint or body filler then no biggie. Other wise its a waste of product IMO
Resident Expert
Not necessarily so. He asked about self etching primer, not etch primer. Different animals. Still not a high build, but fill may be adequate and of course can go dtm.Originally Posted by 88GT
Steve g
A New Member
always get the data sheet with your product and then it will help you on what it can go over and what can go over it. I think it was etching primer that my friend used over bondo and after the car was painted he started seeing cracks. When he sanded those areas he saw the green over his bondo. The instructions were on the can but he never read them. He reads more now.
Member
Excellent advise. Thanks.
Senior Member
Really? I never knew that:o . Could you explain the difference a little more? Also, what is the difference in a "wash" primer, compared to the two primers mentioned above? I don't use any type of acid/etch primer, just epoxy or dtm surfacer. It's just that the differences in the various types of etch primers confuse me. I'd appreciate any replies. Thanks.
Resident Expert
Big disclaimer here. I'm not a chemist, coatings engineer or any kind of expert on the subject. But I will share what I've read on the subject. To etch something is to alter it's surface with abrasives or chemicals. Etching in the context of our useage is opening up the surface with acid. In order to assist in corrosion control phosphoric acids were combined with other acids,chromates and other additives. This roughened the surface and left a corrosion inhibiting coating behind. My understanding is that acid wash and true etch primers were the same or similar. They were translucent or transparent and left virtually no film build. I don't think they are much different than Picklex or Rust Mort, especially since the chromates have been removed from the etch primers. It is used to improve adhesion and inhibit corrosion.
Another reason we use primers is to fill surface irregularities, sanding scratches etc. Here we want the material to build on the surface. There are numerous kinds, the current most popular is 2k (2 part) urethane, but there are many single part primers still in use.
My understanding of self etch primer is when someone combined the two. I have used them in rattle cans, so I know they do build, at least the ones I used did. They're handy to have around to hit that small sand through on the lawn mower you're painting, but on anything I value I use a two part product.
It is my understanding that epoxy is none of the above. I have not seen any mention of the epoxy I use containing any kind of etch acid in it. From my research and experience, their claim to fame is an extrordinary adhesion to bare metal without having to etch the metal. They also have a superior barrier property (subject to limitation). Many use epoxy right over clean bare metal without any rust inhibitors quite sucessfully. Most epoxy's do not fill well and sand poorly, so they are generally just used as a first coat. Some use them instead of etch primers, some in addition to. My regime has been to treat bare metal with an acid metal prep like Picklex and follow up with epoxy then my 2k urethane high build. There are hybrids that combine the high build surfacers with epoxy's (Kirker has a popular one).
That's my understanding. I welcome any additions or corrections that anyone might offer.
Steve g
For many years, I've blasted entire cars to bare metal, then used self etch, followed by epoxy as the basecoats for rust holdout. Then grind areas needing bodywork back to bare metal, apply filler, and use primer/surfacer there- then epoxy again- then topcoat.
Recently I've found out that if the entire car is sandblasted, the self etching primer really isn't needed- you can just use epoxy or urethane 2K primer on the bare metal, then topcoat.
no, I don't advise using self etch over body filler or old paint- not even over primer/surfacer- the acid in the self etch primer, lifts and softens body filler and primer/surfacer and old paint. It's really made to use over bare metal only.
another thing I learned is this- self etch does NOT etch/clean the surface as well, as the old style phosphoric acid liquid etch that would be wiped on with a rag, then wiped off. The old etching compounds seem to "bite into" the metal better, and remove tiny pits left after sandblasting better.
a painter told me one time, self etch will hold out for years- WRONG- if it is not topcoated, you will see rust coming through within a year
same goes for epoxy- the sun breaks it down, and you'll see rust coming through epoxy in about 2 years or so, if it's not topcoated
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