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**Phil Planck** · 01-29-2017, 08:50 AM

At one time I studied this topic quite a bit. As I recall, the downside claim was the chemical process released moisture, trapped under the filler, causing rust on the bare metal. Probably opening up a major discussion

Phil

**tperazzo** · 01-29-2017, 10:48 PM

Thanks Phil,
I'm not a paint expert and there are stories all over the net supporting both sides. Here's what the manufacture says in brief form.

Here's a link to someone who tested both ways.

http://autobodystore.com/filler_&_epoxy.shtml

I gather that today's bondo is pretty good and is ok to apply over metal that is clean and ground with 80 grit. It's done all the time.

Tom

**bbspdstr** · 01-30-2017, 03:29 AM

As has been said a zillion times before, here is "just my 2 cents."
I was trained that ANY filler, even lead, is 'cheating.'

The body makers for Porsche's 356 line 'cheated'...usually with lead.
BUT, there has been other filler found under original paint.

In a nut shell, plastic fillers came along in the late '50s and early '60s, the older bodymen faded away, newbies got lazy or were never taught how to make metal smooth without fillers...and here we are.

Today, true "metal-finishing" is very rare. Most all bodies done by most shops and individuals have some sort of filler, maybe most all types in various places, under the primers and paint.

A very low spot can be filled with up to about an 1/8 of an inch (3mm) and still be "commercially acceptable."

Most bodies done today have a very thin coating of "mud" or "slick" but the majority goes on the floor. It's just for the small dings and scratches, grinder marks and places that just aren't worth the time to "finish." (bump, pick and file) The fillers are just "something to sand."

Where time is money and where past collision work is redone and rust repair is made, a true "metal finished" result, pre-primer, is very expensive, even if the skill level is available.

Some old work that must be redone better nowadays will come in a shop and plastic filler, AKA "Bondo", is removed first with a hammer and chisel. I have seen over an inch. There are sculptures around that use the original remnants of the body as an armature to build the filler on...and sculpt the final, usually VERY smooth, result.

But I digress. Most shops put filler over bare metal. I was trained by guys who were in their 60s when I was in my late 20s, so they are all gone now. Those guys were hired by me when I began my business as not only workers, but really as teachers. They disdainfully referred to plastic fillers as "straightener in a can." They could quickly make metal more straight without filler than a schlepp could with a can of Bondo.

I thought of starting a school before those guys faded away, but the time wasn't right...yet. No Internet in the '70s, no good way to find interested students.....because Plastic was already King.

Anyway, I was trained to be sure the metal was "surgically clean" prior to ANY filling, especially lead. Bare metal that will get a spreader or so of plastic needs some even but serious "tooth" for a mechanical bond, at least 80 grit. The plastic (definition of plasticity, pliable) "plastic" needs to be smoothed out in all directions to get into the roughed surface and not trap air. Each thin layer needs time between applications, needs to be VERY thoroughly mixed and cleaned (raked with a wire brush and blown with compressed air) after sanding and a reapplication of more. Commercially, there is no shame in a semi-translucent coating with small areas of opacity here and there.

Just know that once the plastic filler is begun, unlike lead, there is no further metalwork without starting all over in that certain area.

As far as any filler over an epoxy primer.....there are those who are "sure" it will work OK. I just KNOW that work I did 30 or more years ago with bare metal and a plastic coating over it is just fine today.

Just know that the sanding of plastic coatings is done bone dry, that a waterproof coating is applied as soon as possible (per manufacturer's instructions) and that NO moisture can get in the plastic from underneath...a pin-hole or a tiny missed crack can wreck a nice job in a few years in a moist environment...."or so I've heard."

Bruce

**roy mawbey** · 01-30-2017, 06:31 PM

**bbspdstr** · 01-30-2017, 10:01 PM

"For 20 years it was fine, then area's of micro blistering started and this annoy's me."

Roy, that would happen for me/to me over the years where it was small blisters just over where the lead was. We traced it back to the lead itself, either blasted or just sanded....the surface allowed small contaminants to come out and make micro eruptions under the paint.

Paint, while thought to be waterproof, can allow moisture through microscopic pores and activate contaminants. That all stopped when I learned to take a soft flame and reheat the finished lead prior to filing and allow those slightly sub-surface ingredients to "boil out."

Could be oil or wax, could be tinning acids, could be whatever is in the recycled lead filler itself...or all of the above. All of that is SUPPOSE to boil out when the material is melted and poured into a bar mold. I guess not ALL that left in the process.

Those defects would appear in blasted original lead which opened up the surface or the new lead I would apply, file and sand. It stopped after I began "cooking" that lead filler, another reason most well known restorers and hobbyists don't use much lead anymore; another step that can be a problem if not done just right. I still use it, but primarily on either areas where strength is required (door jambs) or a customer insists and is willing to pay for the extra time it takes.

Most other areas are fine with a catalyzed ground aluminum-filled resin that works like lead, looks like lead when finished and is waterproof. FYI, Brand names are different but the basic product in the can is the same, but that product has a shelf-life, so buy it from a reputable vendor that has turn-over.

Meanwhile, I like lead when it's requested. It takes a while to get back the rhythm, the correct heat and motion, the paddling of the mix of tin and lead as it is just right in it's "plastic" state, etc. The good old boys called that "Packin' solder."

When original lead is melted off an area that needs rust repair, it is saved. So are the filings of new work. They are re-melteed into more bars to use, very efficient recycling.

I was interrupted in my typing of this with a call from my painter who had just found a '57 Chevy Bel-Aire convertible that was parked in a garage of an old guy not far away. Family is selling the property and need it moved...gee, can I 'help'. My dad had one of those and it brings back fond memories...like being with him when he bought it at a dealership...for $2,000 cash. Like getting to drive it when I got a license at 16. Like how much of a "chick magnet" it was...all those things that are now ... just memories.

Bruce

**roy mawbey** · 01-30-2017, 11:44 PM

Bruce,, thanks a lot for that tip on boiling off those possible additives in the lead, you see never knew that. If someone had said to me me in 1976 if you are not sure what you are doing, in 40 years time you will be able to ask a question on your computer and get an answer from a guy in America straight to your screen with even a photograph if you need it inside a few minutes I would have given him a strange look for sure.
Tell me when you sit in that Chevy I think all those memories will come flooding back!!

Roy

Roy

**tperazzo** · 02-01-2017, 08:41 AM

Here's a few more shots showing body work. What looks like primer is not.... It's the skim coat of filler. Whether the car needs it or not the entire car gets block sanded with the filler. Most of it comes off, however my car most likely needs the filler despite all my straightening efforts, ha ha. The alternative is to use lots of high build primer I suppose, but my body guy prefers filler because it is much more stable and tough.

Here's a before shot showing the body file work to check straightness and perform any last chance dolly work.

Thanks for watching! I'm watching too now as it's out my hands! Tough to hand over, but a relief at the same time.
Tom

**JTR70** · 02-01-2017, 01:38 PM

Looks like she's smoothing out really nice Tom! I know what you mean, it was so nice to let someone else take the wheel when it came down to getting my car in paint. Enjoy the ride.
Justin

**bbspdstr** · 02-02-2017, 05:53 AM

Tom, coming along nicely!

FWIW, the best polyester fill primer I have used, and I've tried most of what's been out there, is Spies-Hecker 3508, a catalyzed product that fills well and sands very easily.

It is like a sprayed finishing putty, just smooth and easier to sand with 180. It is usually over metal that's been finished with a thin coating of filler as shown on your shell... as it's basically more.....well, filler. It's what we use to fill sanding cuts and scratches, file marks that were exposed with the spread-on filler, pin-holes, etc. A 'final filler' that is, did I mention?... very easy to sand.

We often use multiple coats with sanding each time with a powder guide-coat. Often, one coat is enough, but if there is a break-through while sanding, we seal those edges with a bit more 3508.

When sanded dry with 180, coats of wet-sandable (and tintable) urethane primer is it's next coating, then the top-coat of color. Funny, all of these products are not "paints".... they are technically "plastic coatings." Gone are the "good old days" of lacquer primer, lacquer putty, lacquer paints, the good buzz from the fumes, then the headaches, then the sand and polish. And beer. Simple chemistry, simpler times.

Continued good luck,
Bruce

**tperazzo** · 02-04-2017, 12:42 PM

Thank you Justin and Bruce,
Here's the build primer to be used on my car.

Just passing info along as I didn't specify this primer, but the body guy really likes it. Seems like a good product although expensive.

I don't have any experience with it, but that's why I'm leaving it to the pros, ha ha.

Thanks again for the comments,
Tom