Body finishing: Order consensus???

B

Bruce/CT

Well-known member
Hi,

I'm sure that this has been debated here before but I cannot find the thread.
I have removed all the old paint off my '36 and have done some lead filling. I want to move on to the next phase of finishing.
Which do I do first: primer or lay a thin sheet of Bondo?
Thanks for your reply. I want to do it correct.
Bruce/CT
 
I want the perfectly smooth base that Bondo can offer. The lead was used over metal pieces were welded in several large repairs.
Bruce/CT
 
Personal I'd do a sealer first then bondo or feather fill. Personal preference, Could be wrong, but seal the metal from moisture. Bondo is porous and adsorbs moisture.


edit: If you haven't painted before. Talk to your paint supplier and have a plan for your paint materials. They all have different cure times/re-shoot windows and compatibility. Make sure they all work together as a team. It could save you lots of money, even if the paint cost more. :).

Deuce really gave you a nice overview of the steps below.
 
Last edited:
When I have used lead, the first thing you have to do is neutralize the acid that you used when you tinned the metal. Scrub it with a strong base. Next I etched all bare metal, sealed entire job with a catalyzed non sanding sealer. Since I have done my metal finishing to within a 1/16" my next step is a catalyzed high build primer. Final block sanding with guide coat reveals any slight low spot that can be fixed with another shot of high build primer or a dab of pourable glaze. After this, final sanding and wet sand, wash with soap and water and ready for paint. I always shoot a last coat of Transtar sealer 10 minutes before color.
That is the way I have been doing it for years. I do all my own work so I spend the time to get the metal real close and haven't had to use plastic filler for a long time. If necessary, you would do that after the etched bare metal and sealer step.
My 2 cents. Most people have their own preferences.
 
I'm with Tinker & Duece on that. You would need bondo to fix the deeper depressions but I don't like bondo for anything more than about a 1/16th deep since it can delaminate with time. If stuff is very shallow then it's just a matter of sand and fill with primers and glazing. If you have dents, depressions, or any oil canning, they should be body worked out as best you can before any filling. Some folks like the shrinking disk on a grinder for the lighter stuff and they do work but it takes time. Hammer & dolly and shrinking with a torch takes time too but it's worth it to me. I hate sanding. I'd rather file than sand.
 
My body has very little in the way of dents or low spots. I just want to put a skim coat of Bondo on so I know it's straight and even. It's probably over-kill but I'm OCD
Bruce/CT
 
A skim coat is probably a good idea, even more so if you plan to use a dark color coat. A properly applied skim coat will reveal even minor imperfections as it is sanded. The advice above to use only materials from the same source is critical.
 
I like to do an epoxy primer over the bare metal to seal it up, then do body work over it. If you are doing a dark color I would recommend finishing it with a layer of slicksand that you can block out to get it arrow straight.
 
I've seen folks slather on the polyester to rough sanded bare metal before which is fine and good for the short term but it won't hold up over time. Metal will corrode right under the bondo. The metal needs to be conditioned to prevent corrosion in the future. A person can use etch with primer over or etching primer since it has the same effect but it needs to be done to decrease the possibility of corrosion in the future. If a person wants to do a lot of sanding, the primer needs to be thick enough and solid enough that it won't easily sand through.
 
rotorwrench said:
Metal will corrode right under the bondo. The metal needs to be conditioned to prevent corrosion in the future. A person can use etch with primer over or etching primer since it has the same effect but it needs to be done to decrease the possibility of corrosion in the future. If a person wants to do a lot of sanding, the primer needs to be thick enough and solid enough that it won't easily sand through.
Click to expand...
The metal under the (Bondo/filler) does not have to be "conditioned".
The only time that it may be a problem is, if it is left to the elements for an extended period of time without top coating it, as the filler is porous and can absorb moisture.
 
I washed the hell out of the leaded area with baking soda wash and then lacquer thinner. Hopefully the acid problem is dealt with.
Bruce
 
Automotive Stud said:
I like to do an epoxy primer over the bare metal to seal it up, then do body work over it. If you are doing a dark color I would recommend finishing it with a layer of slicksand that you can block out to get it arrow straight.
Click to expand...

This is what Southern Polyurethane recommends for their epoxy primer.
 
I won't go into too much detail here, but one thing to note is that the quality (and cost) of materials have changed dramatically in the last 10 or so years. It used to be that I only put body filler over heavily sanded bare metal (36 grit in most cases) - then primer went over that. Now days, many folks will clean the bare metal, use a metal prep to ensure there is not surface flash rust (a source of many problems), scuff again with coarse scotchbrite, then initially coat the entire body with a modern high-quality epoxy primer. This stuff is amazing and it really seals the surface such that you then have TIME to do the body work and not have rust issues along the way.

Also, there are a variety of new DTM (direct to metal) fillers that include a rust inhibitor - they're specifically designed for bare metal. In the old days, we didn't have the variety of filler, primer and sealer choices that we have today.

Many body shops do ALL their skim coat and filler work over the epoxy primer - then they use a high-build primer on top of that - which sands extremely easily and makes blocking and final prep work SO much easier than it used to be. Almost nobody uses epoxy primer for this stage - as it is hard to sand, loads sand paper up, etc..

Then, most folks will use a sealer of some sort - prior to any color/base coats. There are many different types of sealers, with many different tint options. The types of sealers you use may be determined by what you're putting over them. Example, when I'm doing a candy paint with an initial silver undercoat, I'll use a black/dark tinted sealer as it gives more pop to the metallic undercoat.

My best recommendation is to spend some time at a professional paint store that caters to professional body shops and painters - talk to them about their different products and associated processes - you'll learn a lot and will be able to make the best choices as such.

Be prepared to spend $$$ on paint products! The costs are NOTHING like they used to be - one can easily spend $150+ on a gallon of top brand primer (ask me how I know!) - and then you have to buy the catalyst. Also, you will probably need different catalysts for different products - even from the same manufacturer. Don't try to "mix" products that aren't specifically designed to work together - isn't worth the risk.

In the end, it is the quality of the prep work, quality of the materials and how they are applied that will determine the success of the final product. There are many horror stories of folks using miss-matched products, poor prep processes, incorrect dry times, wrong temperature windows, etc . . . only to have adhesion problems and many other nightmares as a result.

Do your research and buy the best quality products you can afford.

Lastly, while I sometimes reminisce about the days of a gallon of black lacquer for $15 - the truth is that the materials today are FAR superior to anything I used 40+ years ago . . . it is not even a close comparison. BUT - you pay for it!

Good luck
B&S
 
Last edited:
34PKUP said:
The metal under the (Bondo/filler) does not have to be "conditioned".
Click to expand...

Suit yourself. I can't recommend any different to folks but I don't use bondo to fill dents. I live in a climate where it will corrode unless you have and air conditioned garage to keep it in. I've heard this story plenty of times but I've had enough years under my belt to see what happens over time with higher humidity conditions and a lot of condensation. Moisture and corrosion form where ever the conditions are right.

I use specific phosphoric acid etches on steel and aluminum and I still use zinc chromate before other priming. I use epoxy primer where I need to level things down since it's a harder coating for top sanding. In aviation it has to be able to take whatever you throw at it.
 
Last edited:
Bruce/CT said:
I washed the hell out of the leaded area with baking soda wash and then lacquer thinner. Hopefully the acid problem is dealt with.
Bruce
Click to expand...

Another thing to consider is how well the lead was laid down. If you paddle it correctly and work it as it should be worked, you lessen the chances of small imperfections, pits, fissures that are hard to clean - only to rear their ugly heads through the paint at a later date.

Truth be told, while we all like the concept of lead as a filler - today it is typically inferior to correctly applied high quality body fillers. Todays 'Bondo' is nothing like the crap from the 50's. Also, over time, there are almost always issues with leaded areas (yes, maybe decades later, but issues tend to surface).
 
I like to bump out the dents before I remove the old paint. I try to metal finish it best I can with the paint still on it. I also know my limitations since I don't do this that often. I gently bump out the dents so as not stretch the metal and shrink any high spots with a torch by heating the spot to the size of a dime and quenching it with a wet rag. I was taught not to hit the heated spot to knock it down as some people recommend because that's only going to stretch it. Then I file and pick at it to make sure the low spots are close enough that a skim coat of filler will finish it off. I don't believe in picking and filing and more filing and grinding away metal just so I can say it is metal finished. Chances are your going to turn it into tinfoil if your not a master metal man. Preserve the metal! I dropped a blob of body filler on my garage floor and the next day when I tried to remove it a chunk of concrete came with it. There is nothing wrong with body filler as long as your not sculpting a car out of it.

When I have the metal work close I sand blast one or two panels at a time at home and prime it that same day. It will rust overnight. You can use metal prep to keep it from rusting but it will never be cleaner than right when it was sand blasted. I don't use expensive etching primer because I have already etched the metal by sand blasting it. The primer is going to grab onto it with no problems. Rather than put a guide coat on the primer to find the low spots I wet sand it with 400 grit. Then I take a paper towel with some wax and grease remover and wipe it down. It will momentarily be so shiny at that you will see the slightest ripples in it. Stuff that you won't see sanding with a guide coat. I circle all those spots with a Sharpie. Then I decide if I need to bump those spots up some more, fill them with filler or block them out with primer. Using the flat palm of your hand and running it over those circled spots if you can feel the low spot "at all'' its going to take filler to get rid of it. Otherwise Your wasting time and expensive primer trying to block it out. It always takes more coats of primer than I think it should to block out a spot so I have learned over the years that when it doubt use filler. It use to be you only applied filler to bare metal, never over paint. Now they have products that will go right over the primer. There is no way somebody can tell you how to do this. I took a college class 35-years ago. I learned a lot but I still made/make mistakes. The best advice I can give is to have a lot of patience. It will be ready to paint when its ready not because you had a goal of having it ready by this afternoon, next week or next month. Every shortcut will show-up in your paint job.
 
You must log in or register to reply here.
Back
Top