Paint and body work...

[kmack]

I have my car stripped down to bare metal. And I'm getting ready to start prepping for paint.

I've heard that it's not good to put "bondo" on bare metal, but to lay down a sealer/primer first, then use the bondo. How correct is this? Is so, then how do I prep the surface of the primer so that the bondo will adhere to it?

[Mike]

Oh man, Kmack, I didn't do my own paint/bodywork. That was something I left to others.

I *DO* know that you don't want to put bondo on bare metal.

Make a trip down to your local automotive paint shop/store. They were very helpful with my project. And, after talking with them, I decided NOT to do my own work. (but, that's just me)

Anyway, you'll want to wipe down the entire car with a bare metal prep of some kind. It's like a thinner. It removes fingerprint grease and other things that managed to get on the metal surface during the sanding process.

But, I'm serious about talking to someone. Do you know of any auto paint stores around your area?

[kmack]

I've talked to a few places already and have even bought some sealer/primer. But I thought Carl B. had said once that bondo on bare metal is a no-no. Something about moisture still being able to penetrate.

I've had a light coat of primer on my car now for awhile. I stripped all the paint off previously and put a light coat of primer to help seal out rust. (It's been garaged this whole time.) I'm sanding off the primer right now back down to the metal. I'm using a rust inhibitor called "ospho" to treat the metal, then I'm spraying the sealer. The paint shop I talked to said this process is ok and should seal up nicely.

But I just wasn't sure about the bondo thing. Hope fully I can get it cleared up soon. I'm hoping to have the door sills, window/hatch channels, and the roof done by tomorrow.

[2ManyZs]

Is the sealer/primer you have sandable? It should be, so just lay on a good coat of primer and let it dry thoroughly, then scuff it up with 220 or possibly a little finer. You don't want the bondo on bare metal, but you should sand the primer to give it a good "bite" to the primer. I wouldn't wet sand it though, you don't want any moisture at all under the bondo, or it will crack and all sorts of ugly stuff. I have seen metal with surface rust under the bondo because the bondo was put on bare metal. Make sure you use the metal prep and a tack cloth after you do anything. That is one thing you can't do enough of, clean, clean, clean. I don't know how I'll ever get my shop clean enough to spray the underside of mine. And it doesn't take much to make a good job look not so good.

BTW, take your time, do it right! I always got in a hurry and it showed! You still have time between now and June, if you get in a bind bring it by here and I'll give you a hand. Sorry, just trying to brighten your day!

[Mike]

Here's a message that Carl sent to the list about this:

>At 8:48 AM -0600 2/9/2002, Kenneth Mack wrote:

>I have my car stripped down to bare metal. And I'm getting ready to

>start prepping for paint.

>

>I've heard that it's not good to put "bondo" on bare metal, but to

>lay down a >sealer/primer first, then use the bondo. How correct is

>this? Is so, then how do I prep >the surface of the primer so that

>the bondo will adhere to it?

Mr. Mack:

According to every study done, that I've read, the following is the

best approach. The US Army did extensive studies on corrosion

control and Consumers Union did long term tests related to auto body

repairs, rustproofing paints and the use of plastic body fillers.

Over the past 40 years of restoring old cars, I've found their

research to be spot on.

Bare metal should be wiped down with something to prevent or stop

"flash" rust. This is the rust that starts from humidity in the air

the instant bare metal is exposed to the atmosphere. You can not see

it at first with the human eye.. but it's there. Mostly usually a

good quality self-etching epoxy primer, applied soon enough with stop

and then prevent flash rust from getting a start on the metal.

After a day or more of the metal being unprotected and exposed to the

atmosphere even with relatively low humidity it should be wiped down

with something to remove the flash rust and something that will

prevent it reforming. Usually this is a weakened solution of

phosphoric acid. I have used a product called OSPHO for many years

with good results.

Once the OSPHO has dried - I believe they recommend at least 24 hours

- you can apply a coat of epoxy primer - depending on the brand and

type of primer you may or many not have to add a metal etching

compound. As far as possible, prime both sides of the metal. The

epoxy primers provide a good moisture proofing seal over the bare

metal.

Then on top of the epoxy primer - you apply any plastic body fillers.

Work the body filler to where you want it. Let it dry... the longer

the better. For really top quality work we are talking weeks if not

months - before final glazing and painting. All of the plastic body

fillers shrink as they dry and harden. The metal should be worked so

that the very thinnest coat of filler is all that is necessary.

Why put plastic body fillers on top of a layer of epoxy primer? All plastic body fillers depend on a chemical reaction when they are

exposed to air or when their parts are mixed, to harden. That

chemical reaction generates heat (in the case of the epoxy based

fillers) and/or it out-gases solvents as it drys (in the case of the

pre-mixed fillers). While this is happening, it can and will

actually draw moisture from the air through the metal. In that case

you get rust under the filler and in a few years the filler breaks

lose from the metal. Once the plastic body filler has dried, if the

metal under it isn't sealed from the filler - the dry body filler

will draw moisture from the air through the metal and the body filler

itself well expand.. We've all seen body fillers bubble up under a

good paint job - and this is why.

All cars manufactured today and in the past 25 years have had plastic

body fillers used to hid exterior metal seams. You very rarely see

factory body fillers bubble up.. the reason is the factory seals them

away from the bare metal to begin with.

Consumers Union ran tests on about 25 different brands of plastic

body fillers (including things like "Liquid Aluminum", "All Metal"

etc etc)... they sealed half the test panels with a sealing primer

and left the other half bare metal... then applied the plastic body

fillers under both conditions to two different places. Then painted

them both the same - then sat them outside to weather. Within two

years every non sealed filler was either breaking lose from the metal

or bubbling up under the paint.

Don't let anyone tell you that the body filler they are using doesn't

require any undercoat - that it itself will seal the metal - it just

ain't so. Don't let anyone tell that the body filler they are using

isn't "plastic" - they all are one type of plastic or another. They

have to be, in order to be able to work them when they are soft and

then have them harden when they dry. Of course the exception is

melted lead;-)...

Properly mixed and applied plastic body fillers will last 35 to 40

years without a problem. Improperly mixed and/or applied - like over

bare metal - they well be a problem, usually within two years.. most

definitely within five years. Depends on what other primers and

paints are applied over them, if the metal is sealed on the opposite

side or not etc..

Bodymen seem to always be in a hurry - they want to believe that it's

OK to slap a plastic body filler on bare metal, get a coat of primer

over it - and roll the car out the door. The salesmen that sell the

plastic body fillers are quick the assure the bodymen that their

product will allow this practice... The ignorant leading the blind..

Don't let them do it on your car if you are paying for and expecting

top quality work.

FWIW,

Carl

Carl Beck

Clearwater,FL USA

------------------------------------

Internet 240z Club - http://240z.org

[Mike]

Good point and a good way of looking at it. Plastic body fillers act like a sponge once they dry/harden. Sheetmetal is porous and it is possible to wick moisture right through it - yes it takes some time... but it

will happen

unless the metal is sealed with a moisture proof barrier which prevents the body filler from drawing moisture.

However I want to make clear (in case of any confusion) there is a huge difference between lacquer based primers, filling primers etc. - and an epoxy primer. The epoxy primer should more correctly be called an epoxy base coat. The epoxy applied to bare metal does seal out moisture and provides a moisture barrier between the bare metal and the plastic body fillers.

You want the body fillers to dry - so you don't want to seal them up completely until they have had a chance to dry. That is why you put the sealing coat under them first - to prevent them from wicking moisture through the metal later and to allow them to dry out to the atmosphere.

I completely agree with Wayne - you have to keep the car DRY until everything is done and sealed up. In effect, you want to seal any body fillers between an inner and outer layer of sealing paint or epoxy primer... but only after the filler had a chance to dry out completely to the atmosphere.

It is common practice in collision shops to apply body fillers and paint the car the same day. You don't want this practice utilized on your Classic Car that you plan to keep for years.

As Wayne mentions - quality shops will allow the body fillers to dry completely, then they will shoot a top coat of paint over the filler. That both seals the filler from moisture once it's dry - and it allows them to see any shrinkage, cracking or sanding marks in the filler after it's dried - but before painting.

Lacquer based primers are intended to help "bound" the paint to the metal and to fill any micro scratches in the metal. They are not intended to prevent moisture from getting to the metal. They do not provide a moisture barrier as a matter of fact they are quite porous.

There are several products on the market that go beyond epoxy primers or epoxy base coats in the area of protecting metal from moisture. POR-15 for example. However you can not get a glass smooth top coat finish over most of them. They are intended as sealers for the inside of the metal or as base coats for the under- carriage. (see http://www.por15.com).

FWIW,

Carl

>At 9:03 PM -0800 2/9/2002, waynekarnes wrote:

>what Carl said !!!! may i also add, all plastic fillers ( i.e.

>bondo ect. ) will act as a sponge, wicking any moisture it can out of

>the air ( especially a cool evening ). do not let yourself be fooled

>into thinking, that you can spray primer over the bondo, or any metal

>where the paint has been removed, and protect the metal from rust.

>moisture goes right through primer and oxidation of the metal results

>in rust. which if not removed, will cause your million dollar paint

>job to bubble right off your car. in some cases, water goes through

>the primer, through the plastic filler to the metal body, the body

>rusts under the filler and, only the elastic properties of the final top

>coat of color paint, holds the filler in place. this is why you will

>often see a project car with different colors of paint sprayed here and

>there. left over paint, sprayed over primer to seal it, and then used

>as a guide coat when sanding.

> if doing your own work, remember to keep the car dry and out of the

>cool air, if you need to drive your car, before you can paint it, find

>a way to seal it. if having a shop paint it, if it's only covered

>with primer, ask them not to leave it outside at night, or in moist

>air ( fog, rain, ect. ).

> of course, there's a chance i might be wrong ... Carl ????

>

>Carl Beck wrote:

>

>> Mr. Mack:

>> According to every study done, that I've read, the following is the

>> best approach. The US Army did extensive studies on corrosion

>> control and Consumers Union did long term tests related to auto body

>> repairs, rustproofing paints and the use of plastic body fillers.

>> Over the past 40 years of restoring old cars, I've found their

>> research to be spot on.

>>

>

[Rattfink]

Great reference material! Thanks for taking the time for the thorough post... I'll be needing that info all too soon.

'Fink

[Guycali]

Thanks guys for the great detailed info. I've always had questions about the procedure in restoring a Z from the bottom up. After a Z is completely strip off of paint and rust to bare metal and applied expoxy primer, what's next in terms of restoration procedure? Here's what needs to be done.

1. Rebuild/modified engine.

2. Swap transmission and differential.

3. Rebuild/customize suspensions.

4. Attach fender flares or body kits.

5. Install roll bar/cage.

So when does painting the Z come into play here? Should the interior and engine bay be painted first after the expoxy primer or leave everything unpainted until all components are ready to be installed? If I want to rustproof the undercarriage with some kind of "tar" or the likes, should I do it immediately following the expoxy primer? What is the procedure you'd mostly take on given the above works required? Thanks in advance.

-Guycali

[EScanlon]

I've learned a couple things from this post from what I was taught. The epoxy primer under bondo is new, but then again I was a body man back in 1983, funny thing, that's what I did on several panels of a 1976½ Mercury Capri II, but not on all, and yes many years later the parts of the car that had the bondo falling off were the un-primed ones. Just goes to show that the learning goes on, and what "everyone knows" does change. The old bondo on bare metal was what we were shown by the factory reps pushing their product. In fact, they would do it the same way.

One note though, and this is critical. No one has pointed out that epoxy primer can be top coated or have other coatings put on it within a short period of time after it's been shot. After that time period, you MUST scuff off or sand off the top "skin" or even paint won't stick to it properly. This varies by manufacturer, but for the most part it's betwen 24 and 48 hours. Since you do have to let the epoxy set, shoot it in the morning, and bondo in the afternoon.

I still want someone to discuss whether or not the panel should be prepped with a slap-grind of 24/36 grit to leave gouges or teeth for the bondo to adhere to.

Regarding GuyCali's question about sequence of events:

For what it's worth, on all the cars that I've worked on, and even at the body shop I worked at, we had one adage: Get the Mechanical work done first!

In fact, the body shop where I worked was owned by a large trucking outfit, who ALSO owned it's own mechanic shop. Any truck would FIRST go to the mechanics who would totally rebuild the truck, engine, tranny you name it. When they were done, then and ONLY then would we get the rig. If there was something we had to do in between their mechanical processes, we would get it in on "loan" (painting engine compartment, engine, tranny) and the unit would go back until it was ready for BODY work.

So, my advice, and using the items you listed, my numeration would be:

1. Rebuild/modify engine

2. Swap transmission and differential

3. Rebuild/customize suspension

4. PAINT INTERIOR (or make sure paint is good)

5. Install roll bar/cage.

6. INTERNAL PAINT TOUCH UP (check for damage)

7. DO EXTERNAL REPAIRS TO BODY PANELS (dents, etc)

*8A. If Fender Flares / Body Kits are the weld on or graft on type then do these next

OR

*8B. If they are the bolt on type I would attach and then REMOVE them from the vehicle.

9. DOUBLE CHECK BODY for damage from flares / body kits.

10. PREP FOR PAINT; BODY AND ANY PARTS TO BE ATTACHED (Final out repairs, bondo; Prime vehicle and wetsand smooth)

11. PAINT BODY AND PARTS

12. UNMASK CAR====THEN WALK AWAY (this is critical)

13. LET PAINT CURE FOR 2-3 DAYS

14. CAREFULLY remount external items to car (Bumpers, painted parts, emblems etc)

15. WASH CAREFULLY WITH ONLY WATER AND DO NOT WIPE HARD WITH RAG.

16. WAIT NO LESS THAN 90 DAYS FOR WAXING

That's my 2¢

[26ounce]

Very informative thread this one. My thanks to the contributors.

Just a question to EScanlon and anyone else who may have some good advice; My 260Z is suffering from a dodgy paint job, it looked good when I first bought it, but now there is rust coming through on most of the panels (I've only had it for 6 months). I really wanted to do the mechanical work first but the way the rust is appearing it looks like I have no choice but to do the body work immediately.

Is there a reasonable way I can temporarily patch up the body to stop the rust, a quick fix so I can do the mechanical bits and postpone the body work until I have saved enough cash to do it right.

Could I just strip off small rusty areas, paint over with POR-15 and then bondo and paint to match the rest of the car?

[EScanlon]

I'll give you a better answer after you describe HOW the rust is "coming through."

This is critical as there are two possibilities for the source of the rust.

From the top because of :

Paint : Faded / missing / sanded off

Previous Paint Job leaving car in primer.

OR

From the underneath because of:

CANCER

This type of rust through is the most critical to address immediately. Suffice it to say, if it's already rusted THROUGH the metal, can you imagine how LARGE the area is in back?

My personal policy regarding this type is to immediately examine both sides of the metal. Sometimes you can remove the fenders and look behind, other times you can remove interior panels and see.

In either case it does involve some disassembly and may or may not be quick and easy.

I started addressing a fuel leak from the gas tank a year ago after having lost the right rear wheel @ 60+ mph. (long story; and ask Zvoiture if you want ME to tell a long story).

A year and 6 weeks later, I am finally getting close to getting the car back on the road. I'll be posting a bunch of pictures and will write several pieces on it.

To give you a general answer to your questions:

Yes, and No.

Depending on the type and amount of rust you MIGHT be able to POR-15 the back of it and put everything on PAUSE or actually; really SLOWING it down. Notice this wouldn't STOP it.

BUT

Sadly; rust through on the panels from the back may or may not spell the end for a car. It just depends on how much you are willing to chase it. This means $, and not just $, but $$$$$$$$.

Rust from the top, as long as the underneath is sound can usually have a quick shot of Sealer sprayed on, whether Rattle Can Paint or Primer SEALER. But note that regardless of how "good" it looks it IS RUST! So you need to come back to it soon and FIX IT.

Enough, let me know what type of rust you have.

[26ounce]

The rust I am referring to is from the top.

The previous owner had work done removing cutting the serious rust out and replacing it with metal, as well as putting in new floor pans. Unfortunately, it was also resprayed white (used to be blue) and there are some problems with the job. There are noticeable cracks in the paint, and the paint seems to chip off any edges quite easily. Rust is forming in all these cracks and chips.

Now that I read your post however, I will go back and check all the backs of the panels where possible.