Does these readings appear to be original paint?

[Fairview]

On an 84 911, I am seeing paint meter readings that vary from 4 mils to slightly over 7 mils. Does that range seem consistent with original paint? Thanks

[962porsche]

yup it does. how ever the 7 could be a repainted panel? with just being a a few coats of color or clear over it. the common is 4 to 5 for a factory finish but I have seen a few factory finishes with up to the max of 7 mil's.

[Fairview]

Thanks 962.

There appear to be no signs of repaint that I normally look for (sanding marks, overspray, inconsistent gloss or texture, mismatch of color, evidence of tape edges, including along and under the rubber seals for the glass). History of the car seems to bear that it is original paint, too.

I appreciate your help with the interpretation of the paint meter readings, I'm so old school I'm not used to these new fangled gadgets.

Thanks for the input!

Jeff

[962porsche]

mil gauges have been around for a long time!
but yup my guess is your looking at the OE finish.

[arbezc]

Hello 962, you input is musch appreciated.

Does your spec of 4-5 mils for factory paint include their primer? I'm working on a 73 911 originally painted Metallic Blue code 324.

Could you suggest approximate target mil builds for primer, base & clear? I plan to strip the outer body to bare metal & wasn't planning to do much colour sanding. I also intend to apply the primer & block sand myself. Final painting will be done by a professional shop.

Thanks

[962porsche]

yes the mils includes undercoats.
mils are measured from the substrate.
it's going to be very hard pressed to try and match the factory mil builds from a repaint out of a shop.
there are many reasons for this one is that the factory doesn't use filler primer cars at the factory are only sealed.
at the factory the cars go thru a dipping process this in many cases is the 1sr black layer of material over the substrate. about 2 mils
then the cars are sealed this is in most cases the very very light gray ( almost white) layer about 1 mil.
then the cars get there top coatings. single stage about 1.5 mils , base clear about 2 mils , tri colors about 3 mils.

your saying you want to strip the cars finish off to bare metal.
you will also be stripping off the galvanized layer. this will need to be replace .
in most cases you replace it with a etch or epoxy primer.
this will give you a mil build of about 1 mil or just under with two coats after drying.
then say your going to spray a few coats of filler primer to go over any body work and to give a good substrate for block sanding. this will be about 3 mils for two coats. or about 1.5 mils per coat you spray.
now if your going to do a sealer and it's kind of recommended to use one if you want a uniformed coat for better coverage and if the car will not be sanded and painted in a 6 hour window.
this will give you 1 mil or just under.
a single stage finish will give you about 3 mils
a base clear will give you about 1 mil for your base and about 3 mils for the clear.

a good block sanding will remove about .5 to 1 mil of the filler primer. any more than that the primer could fail later on down the road. with shrinking in and poor hold down.
a real good color sand and buffing will remove about .5 to 1 mil at most. and again any more than that the top coat will fail later on down the road. with lifting and pealing top coats offering little to no UV protection.

so most bare metal repaints will give you about 6 to 8 mils of product.
at 12 to 14 mils a car should be stripped or the top layers of be sanded off.
in many cases if there is nothing wrong with the OE finish like checking pealing or other major problems it's not usually a good idea to strip a cars finish off down to bare metal.
in most cases the best metal protection you have on a cars was put there from the factory.

[arbezc]

Thanks for such an informative response 962.
Unfortunately the paint of the hood & fenders is not very good. I've found some non-factory primer on the hood. You're correct, the original primer is a very light grey, almost white. I assume Porsche's were painted manually in 73.

My newly calibrated paint meter shows readings from 5.2 to 6 mils. (actual thickness could be a littlelower as the car is a bit dirty) I could leave most of the outer body & paint over it but I'm concerned about some heavy scratches the car collected in storage. Do you recommend a #120 disk to sand the base/clear down to primer?

At the moment I'm welding in some patch panels. I'll need to cover the bare metal in epoxy. I've spayed up a text panel with 3 Epoxies: Corlar 825S, PPG CRE-921 & PPG Aquapon. (Its very difficult to find the SEM primer in Canada) Mil thicknesses with 2 coats ranges from 3.3 to 5.2 mil. This is much heavier than you recommend but this paint is planned for the inner fenders & underbody. It will be topcoated with something to replicate the EOM undercoating & only dusted with overspray as original.

Does your recommendation of 1 mil epoxy primer apply to the wheel wells & under body or could I go a bit heavier since there's no top coat? I assume you wouldn't use filler primer in these areas. It will take some practice to maintain a 1 mil build in 2 coats.

Thanks

[962porsche]

I sure hope you didn't start mixing your primers and spraying one over the other?
even just using different primers and products is not a good idea at all.
what should be done is you pick a product line and use the products with in that product line.
so if you need lets say an epoxy primer to protect the bare metal areas and you started with say the RM paint line you would want to then use the RM filler primer and then the RM sealer base coat and also clear coat.
the worst thing is to start playing chemist and start using say Corlar then use another brand of filler primer and then yet another brand over that. this will just give big problems down the road after the car is all done and you have countless hours and money into the project.

when it comes to undercoats ( I'm not talking about the black rubber crap that in no way should be used on a car) undercoats are primers / sealers MORE IS NEVER BETTER!
reading the TDS sheets is very important and is a must to do when using any product.
if the TDS states only 1.5 to 2. mils than this is all you need to apply on the car.
they product is designed to give you the most protection at that mil/s and more could and will lead to bigger problems.
when we replicate the way say Porsche did there wheel wells we only would spray two coats of epoxy primer over the undersides of the wheel wells then spray the stone/chip guard over that. should be no need to spray a filler primer in those areas.
again more is never better.

[manbridge 74]

Been in the biz long enough to almost never use a gauge. I can spot the over thick repaint the moment they roll into the shop. Had a rear deck lid on a 71 recently that was so thick that the lettering badge posts were hardly long enough for the fasteners. Entire car looked dipped in chocolate (sepia brown). And this, a car restored to the “highest” level in Hungary. Nothing compares to the OE finish in almost all cases.

[arbezc]

Thanks 962,
No, I don't plan to mix primers. On the top side I plan to stick with the system the painter will be using. The shop I'm considering is Porsche Classic approved & uses Glasurit.

The primers I'm testing are aimed at the underside & inner fenders only. I'll heed your advice regarding the TDS. All but one of the primers I'm testing is within the recommended mil build. I admit to coming from the "more is better" schools but I'm learning. Here's an image of a satin black test plaque & ran on the front of our daily driver last winter. Various paints are labeled across the top, metal prep & primers run horizontally. Bare metal was exposed between each test patch.



Our winters are very hard on cars, temperatures hover around freezing, therefore lots of water & salt. The best performing satin black was PPG Aquapon over Wurth Zinc Spray Light.

manbridge:
I wish I had your level of experience but I don't, therefore the reliance on measuring. Your comment regarding the dipped look of too much paint triggered me to check a motorcycle fuel tank I had painted. It looks very glossy but too rich, not Italian original. Sure enough it’s reading 13.2 mils.

[962porsche]

I used to do lots of test panels. they are not a bad idea to give you real world views on products.
when testing primers AKA undercoats you have to take into consideration that undercoats are not designed to stop or hold out moisture from going thru them. this is the job of the top coats and only the top coats are your moisture barrier.
zinc is one of the best rust inhibitors but zinc primers say like a weld primer you can rub off with your finger. so by it's self makes for a not so good undercoat product.

I don't remember if your applying a stone / chip guard on the undersides of your cars chassis?
I think you stated you were looking to replicate the OE way the car was done?
because the stone or chip guard will be your moisture barrier this will also be very important.
you hear lots of people using products like truck bed liner for stone protection. using a product like this for the chassis on a car is a bad idea.
bed liner will take a scratch well but doesn't take the sandblasting from what your tires are kicking up very well at all. the reason is it's not a soft material. it dries to a hard surface and being so the sandblasting from the tires will blast thru the bed liner much faster than a stone or chip guard.
stone or chip guards have some elasticity to them and this resists the sandblasting.

[arbezc]

Yes, I’m aware that primers shouldn’t be left unprotected - I wanted test them under severe conditions.

On the panel above the 1st four columns are rattle can satin black paint. The last 2 are epoxy paints. The first row has Corlar as a primer; the second row uses self-etching & zinc primers, the 3rd row is paint on bare metal. I abraded each section with a sand blaster & a scribe before mounting to see how well the samples resisted undercutting by rust. As you can see the rattle can paints didn’t survive one winter & nothing did well without primer. I was surprised that the best performer was an industrial epoxy over a 96% pure zinc primer. It adhered really well along its edges.

By “undercoat” I meant stone/chip guard. I read most of your comments regarding their application. I understand the original 3M material used in 73 is NLA but Upol supplies a decent facsimile. The chip guard on my car is in very good shape other than the front wheel well which I stripped years ago. I was planning to sand blast a few loose spots that and apply epoxy primer then replace the chip guard.

I’ve re-measured the primer on my latest test panel. I’ve applied 50 to 100% more material than the TDS calls for. Looking back, I also used more paint than called for on the cars I painted in Imron. Can you suggest a simple way of monitoring film thickness as you are spraying? I’d like to focus on the durability of primers right now not so much top coats.

I assume you want to standardize your tip & air setting up as per the TDS and spray uniformly with the paint flow trigger full on. Most TDSs call for “medium coats or wet coats”, is there a way translate more clearly? Something like “one light coat then apply a second until glossy”? I have a wet film gauge to practice with. Maybe spray some test panels that appear too light & verify once dry?

Thanks for your help.