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The only fly in the ointment is that if you have a car of many colors ( ie bondo color different then the majority of body panels etc ), it will probably take extra coats to reach 100% color coverage on the whole car.

The main benefit of using a primer is that it seals the bodywork so that the initial coats of paint over the worked area are not sucked in like fresh paint on an old wall.



I would say the bigger fly is not properly blocking or reducing any waves - especially if you have a collection of repaired and painted surfaces underneath. If you are doing any repairs other than just scuffing your old paint and going over it, and you are putting the paint on something more than just a beater that you don't care about - I say prime the whole thing and block in a more traditional manner as much for this reason as any adhesion or colour coverage concerns. In this case I hit any areas with bare metal with an etch primer first. Sherwin Williams makes great stuff in a can. GBP 988

Either way, with respects to adhesion, many of these paint manufacturers of any alkyd enamel DTM "rust paint" will still recommend a priming before hand to achieve a uniform surface that they can more confidently claim good adhesion among other reasons. Mind you, I've never had any real problems with this stuff flaking off - it does pretty much stick to everything ... I'm just saying...

Colour coverage is definitely an added benefit, but I would say the prime reason (hehe, sorry), for, err, priming it first, is for a nice smooth surface as much as anything.

Past all that, cleanliness is VERY important. I'd still use a good quality grease/silicon remover that leaves no residue vs. mineral spirits. And a tack cloth.

As an aside though, with respect to priming for blocking and prep purposes, I have found that the paint I am using, Sico Corrostop...



...sands extremely well. I've found putting a regular thick coat on blocked really well on one piece I was painting. Not sure how many coats would be required to match the at least 3 coats of high build primer you should use, but I'm going to experiment some more in that department.