Preparation, priming and sealing of bare metal patches

[JohnJL]

Hi all,

I am a sheer novice on bodywork, but I am willing to learn, patient and careful. With a bunch of repair an patching, including replacing the front pan, tank support and part of the frame.

There are 2 symmetrical rust problems on each side of the chassis where the corner of the door's rear edge and bottom edge meet.

The rust is all cut out, glass blasted, welded in new metal, formed ne panels and fit them in place. I Then blasted them again.

I have assembled a number of rust converters, metal prep, degreasers, primers and coatings.


I am tackling this in pieces. The front end took me three weeks, the sides another 3 days, and I have some more in the engine bay and rear suspension points.


I have been using a braided cup brush or wheel to clean up the metal and my welds as I go, as pictured on the left of the last pic.

I have then been using rust converter, rinsed, then metal-prep. My first question is as follows; Should I then be priming, or first seam-sealing then priming?

Next question: as I am doing this in pieces over a year or so, whats the best product to use to prime-as-I go? Can I use Krylon primer as I go, or is the 2K primer better? I haven't settled on the final paint yet. I have sprayed before, but I am considering a roller like Jury did. I have all the hvlp equipment already and the space to do it.

I am looking for some advice as to what I should use to prime as I go, a rust-preventing coating that can sit for a year, be thoroughly cleaned and degreased, then begin the filler-sanding-primer-finish cycle?

Here are some pics of the repairs and products I have on hand.

[962porsche]

a rust converter only works on rust so if the metal has non on it there is no need for it .
I'm not a fan of rust converters but we do use then down inside places like rockers that may have a little rust on them .

as for a area like what you have posted w would handle that in one of two ways .
for areas like that where your closing them back up by installing the outer panels in this case the QTR we would spray a E-primer on the bare metal as it keeps getting it's self boxed back in .
we would also use SEM rust-shield for this too at times .
we would pick one or the other depending on the job and what the customer was looking for .
if it's a concourse resto we would use the E-primer using the same color of the E-primer as Porsche did .
if it's a non concourse resto we would use the rust-shield as it is a better product to hold up to use .
E-primers are etch or epoxy .
personally I would pick for this job rust shield as it's not a concourse resto .
if it were a concourse resto I would pick a chromated etch primer the same color as porsche used .
the rust-shield is a all on one product so it's a under coat and top coat all on one .
it can be used over primers paints and DTM (direct to metals) it offers lite rust hold out as it has a rust converter in the product . but not to the amount of a full converter does .
in places were your welding you would use a weld thru primer for those areas . after your all finished welding you coat the area again with rust-shield or for concourse a e-primer .
for the outer surface of the QTR , rocker and so on you would one use one type of product and that would be a E-primer over the bare metal then a fuller primer over that .

[bpu699]

962porsche, as a follow up to the OP question, can you offer an explanation of why rust sometimes seems to come right back despite using epoxy primer/paint? IE. What are the mistakes to avoid?

I went through almost exactly what the OP did on a prior porsche. Sandblasted a front fender down to metal, used the dupont metal prep. 2 coats of epoxy primer (not sure if chromated, I think it was the OMNI line), and then single stage top coat. Looked great. 1 year later, having taken the car for a drive in late fall where the city salted the roads, it started to blister the following spring. Exactly where the rust was.

Had the same scenario on a white ford e350 cargo van. Sandblasted the rust spots, dabbed on some white rustoleum... 5 years later, 5 salty winters... no rust.

Is the epoxy primer/paint just not that good? Or, is there something that us novices are screwing up? The rustoleum seemed to work way better.

Bo

[JohnJL]

Thanks for such a thoughtful response. It is indeed not a concours job. Would the 2k or krylon primers i have there on hand in the pic be suitable?should i keep using metal prep before priming, as in the 101 thread?

Thanks!

[JohnJL]

Thanks for such a thoughtful response. It is indeed not a concours job. Would the 2k or krylon primers i have there on hand in the pic be suitable?should i keep using metal prep before priming, as in the 101 thread?

Thanks!

[962porsche]

Originally Posted by bpu699

962porsche, as a follow up to the OP question, can you offer an explanation of why rust sometimes seems to come right back despite using epoxy primer/paint? IE. What are the mistakes to avoid?

I went through almost exactly what the OP did on a prior porsche. Sandblasted a front fender down to metal, used the dupont metal prep. 2 coats of epoxy primer (not sure if chromated, I think it was the OMNI line), and then single stage top coat. Looked great. 1 year later, having taken the car for a drive in late fall where the city salted the roads, it started to blister the following spring. Exactly where the rust was.

Had the same scenario on a white ford e350 cargo van. Sandblasted the rust spots, dabbed on some white rustoleum... 5 years later, 5 salty winters... no rust.

Is the epoxy primer/paint just not that good? Or, is there something that us novices are screwing up? The rustoleum seemed to work way better.

Bo

as to why or what happened I really can't make a good reply to .
I don't know the OMMI line so not knowing the TSD on each product as to what 's in it and the use it's for I really can't say .
my guess it's the epoxy primer was not chromated ?
then if it rusted in the exact same place that kind of tells me not all the rust was removed ?
as if it was then it would not just rust right back thru in the same spot .

there is no saying how or why rust just comes back what ever you did on one car did not work and it worked fine for the other . it you pick a system and pick the right products and use them as they state in the TDS then there is no reason why the product should or would fail .

[bpu699]

Thanks for the input. I appreciate it.

Bo

[962porsche]

Originally Posted by JohnJL

Thanks for such a thoughtful response. It is indeed not a concours job. Would the 2k or krylon primers i have there on hand in the pic be suitable?should i keep using metal prep before priming, as in the 101 thread?

Thanks!

I'm not a fan of the 101 thread personally I find much as not the best way to do things.


as for the products you have you would have to go thru the TDS's on each product 1st to see just what they do and if that is what you need them to do and 2nd is to see if they are compatible with one another .

it comes down to using a system .
you pick a paint system and use the products from that system you have picked .

from what I have seen on many autobody forums is people tend to try and over do metal prep . they wipe and spray more crap on bare metals in hopes it's never going to rust and what really happens is it rusts faster .
clean bare metal should not need all types of preps and conditioners .
all it needs is a pre priming wipe down with a cleaner made for metal . wiped on with one clean rag soaked in cleaner and a dry clean rag to wipe the cleaner back off before it drys on the panel .
then a proper coating with the needed product like I stated in a earlier reply .

things like just sand the bare metal with the proper grit before you apply any product makes a difference .
no sanding ,to fine of a grit or to course of a grit and a product may not stick .
not wiping down some right you may get the same thing happening .

when you buy some thing you should never say (well I try it ) you have a bench full of products . again you should 1st know what your trying to achieve with the product you are picking .
then see if the product your using will do that job . then see if it's compatible with other products your going to use .

some primers/undercoats you can not go over products like metal preps that you wipe or spray on and leave it on the panel .

when you buy a epoxy or etch primer be sure that it's for metal rust protection if your looking for metal protection . it is because not all E-primers will give you that some are just simple primers like medium and high build .

[JohnJL]

Fininshed up the rail rust repairs and door jambs and fenders.