Epoxy primer under body filler?

I've been told the new thinking is to use epoxy primer-sealer under body filler. Can anybody elaborate on this? I'm assuming one uses an epoxy product like the PPG "DP" series?

Does the filler have to be spread over the primer within a certain window of spraying the epoxy? I like using evercoat rage or rage gold filler unless its over a weld.

Any downsides? I was always told grind down and lay the filler on bare metal. This is a new concept.

 

It must be! I have been told the same thing. All I was told is once the primer drys they rough it up with 80 grit then go on with body work. And by all means I'm not a body man and not a professional. Just have talked to them. They all use the ppg dp epoxy primer and have had very good luck

 

I do not like it my self. I do not like the way it rolls up around the edge. Grind mud prime and prime works for me.

 

They have discovered that the chemicals in the filler would eventually oxide the bare metal. That is why you see surface rust under the filler or bubbles over sometimes. Nowadays, primer seal first, then apply filler as needed.

 

Here is what I do.

Get the panel to a rust free bare metal piece, wax and grease remove, then I spray DX1791 self etching wash primer. Then I spray two coats of DP90, the black shows the dents and imperfections better. I usally wait overnight to apply filler. You can appy it straight to the DP within 7 days with out scuffing but I usally scuff everything with a maroon scuff pad. Then apply the filler, I use rage gold.

Here is a pic of a Duster with the filler applied over the DP in this pic it is ready for slick sand.

 

Not true. There is probably not a collision shop around that prime under filler and they don't have any problems. The problem lies when guys put filler over bare metal and then let it sit exposed for long periods of time without priming over it. The filler absorbs moisture and corrodes the metal.

If you are priming right after you apply the filler no problem over bare metal if the car is going to sit with just filler on it prime under it.

 

I have done both. I still prefer filler straight onto bare metal as it feathers out nice and will be there forever if the metal is properly cleaned.

I like the DP epoxy when the car has to sit in bare metal for a long time. If the body is coated with DP, you can take your time on the body work without worrying about the bare metal rusting. Just scuff the DP in the area you are filling with 80 grit and apply filler as usual. My 36 Nash was done this way 11 years ago and the paint still looks like new.

 

All I can say about this is read the can..... I have been doing restoration body work for over 30 years..... I have NEVER seen instructions on a can of filler that said to apply over any type of paint or primer..... It always says bare metal sanded with at least 80 grit..... Just my lowly opinion......

 

Now there is epoxy based bondo. And everything thing bare metal should be covered with an etch or epoxy primer before filler primer/surfacer.

 

do you know more about this? I would assume the epoxy based filler is better at not absorbing water? remember paint and body technology stuff changes, usually for the better, if the new products say to use epoxy under them, then I would do it, just be glad we have such good products today over what used to be available, this is one area where traditional isn't always better, I remember "traditional" filler and how bad some of it was compared to new products, I've even learned to lead for the sake of doing it, anything that can give you a better finish and last longer is always good in my book, the traditional parts will always be nicer knowing your paint is going to last

 

We've used it at our shop. Evercoat has it in their product line.

 

http://www.google.com/url?sa=t&rct=...0IHgBg&usg=AFQjCNED_gBzh9NUfgaolDQYFGAQpQZZBw

 

thanks I put my off topic car in primer and even though it's inside,some of the small amounts of filler went bad, I'll have to try sanding it out and trying this

 

If you had a door that was professionaly sandblasted, and now had rust free rust pitting would you prime or fill first? Would one bond better to the pitting? Bob

 

Bob, I would sand it with 80 grit, wax/grease remove, spray a coat of DX1791, then a couple coats of DP90. Let it dry for a few days scuff it down and apply rage a quantum filler. I have been doing it this way for 10 years never had a problem.

 

There are pros and cons to doing primer under filler. This is a past discussion of the topic:
http://www.jalopyjournal.com/forum/showthread.php?t=681063&highlight=primer&showall=1

 

I would go by what the filler manufacturer says, they know their product,they designed it, why are we arguing with them? the old ways of doing things don't always apply anymore, new products are light years ahead of the old flilers and primers, a lot of products are different, you can't do a one size fits all approach

 

If you're gonna do it etch prime before your epoxy prime the bare metal

 

I was on board with this set up until I was reading the tech doc for dx1791. It said not to use it on media blasted steel...I will be media blasting my cab soon so need to find something that will work under the dp90..

 

Etching primer contains phosphoric acid. You could just treat the surface with phosphoric acid then prime with DP. Done properly that's actually better than using etching primer. I seldom use etching primer when it's practical to do the etch manually.

 

Autobody filler is (basically) made of a vinylester or a polyester type resin.
Epoxy primer is (basically) made of an epoxy type resin.

If you were to bond/glass over a metal pad to a fiberglass boat,
vinylester or polyester is never used, epoxy is.

There is no way a plastic resin can make a chemical bond to metal,
it's going to be a physical bond.
Epoxy has better flow characteristics to grab into those microscopic imperfections and grab on.
Now that the metal has a bonded resin coating,
the vinylester will stick much better to the epoxy than the steel,
especially if the epoxy hasn't totally cured (7 days or so)

If you are bored one day,
do a test patch on some scrap sheetmetal.
One the metal-filler-primer vs metal-primer-filler.
Take a hammer and see which one sticks better.

TP

 

I was hoping that was the case. I just read this on the dp90lf tech doc

"FILM BUILD OF 1.2-1.5 MILS OF DPLF IS REQUIRED or the surface must be treated with metal cleaner/conditioner or coated with dx1791/1792"

What exactly is that saying? Does that mean enough coats so that it is 1.2-1.5 thick, and if so you dont need anything under it?

When etching with phosphoric acid is the proper way to spray the whole surface, then rinse, let dry, scuff and spray dp90?

 

Good info....

BTW, where is a good place to buy these PPG products?

What is a good PPG high build primer to use over the body filler? I plan on using rage gold or extreme...

 

I don't know what that's about and I have never heard that. I always use a generous application of DP, let it fully cure, then sand(yes, it CAN be sanded.

I apply it with gloves and a rag keeping the part wet. When the color has fully changed it's done. On clean metal it doesn't take long. Some products say you can just let it dry then prime/paint. Some of those same products leave what is supposed to be a paintable residue. While the part is still wet with acid I always rinse with clean water to remove all possible residue, then immediately blow dry with compressed air. As soon as possible after the part is 100% dry and back up to ambient temp, apply the DP. Scotch-Brite is helpful when treating some parts. Scotch-Briting or sanding after treatment will damage the protective surface produced by the acid. For even better protectiuon and paint adhesion you can follow the acid treartment with a product that creates a better layer of zinc phosphate on the metal. That's how production parts are done.

I have used the described method on LOTS of parts over 20+ years. The only time there was a problem was painting magnesium that hadn't been properly pre-treated(requires a different process).

 

You are right, epoxy adheres to metal better than body filler. But, body filler adheres to clean roughened or blasted metal significantly better than it does to primer. I've tried both ways. On a car it may not matter either way, but on the mechanical displays I built it was necessary to tighten bolts and nuts against filled and painted surfaces. I found that primer over filler has much better overall adhesion than filler over primer. If the filler adhered as well as primer that would be ideal, but what I described is the best compromise if max possible adhesion is really an issue.

 

The question you have to ask yourself is not whether the filler will stick to the bare metal, or the prime better. The real question for me is which one protects the bare metal better long term?

I do agree, collision shops apply body filler right over bare metal all the time without much issue. But you also have to realize that most shops replace parts now a days rather than perform major body filler work. And also, how long does your average person own their daily driver now? The life expectancy is far less than doing a hot rod or custom car. Just because a body shop does this on Mrs. Smiths Ford Taurus doesn't make it right now does it?

And going by the filler companies recommendation really holds no water for me either. They are not the ones that will get the phone call when there is rust under the paint job and the paint is now failing. The paint company does. Body fillers will stick to most everything, agreed. But that doesn't make it right.

The big reason for primer (DP type) on bare metal first is to protect the metal from any corrosion. Body fillers create heat when they dry, which can create moisture. Right on bare metal. And what if that perfectly prepped panel that everyone speaks of wasn't really prepped perfectly? What if there was some really small contamination left over and body filler was applied? Rust! Epoxy primers and etch primers have sacrificial pigment that will help keep the contamination from growing/ spreading.

The big reason why it says no etch/wash primer over sand blasted steel is because they are so thin. They will not stand up to the profile of the sandblasted metal. Think of blasted metal profile looking like a mountain range. The peaks will stick out of the top of the etch/wash primers and will sit in the valley's where the epoxy has enough film build to cover the entire profile. If you sand the panel or parts well enough, then you can etch/ wash prime first.

A body shop I deal with had a early 70's Mustang come in after an accident. The car had once before been repaired and repainted at another shop years before. There was body filler all over the bare metal of the hood before primer followed by paint. From the accident the filler (a skim coat really) all came off exposing tons of surface rust on the metal. It had been slowly growing under there for years. Just because you can doesn't make it right.

 

ive been told NEVER apply epoxy primer or filler over etch primer.The acids in the etch will cause adhesion problems with filler and epoxy primer.I apply filler over bm.Then epoxy prime. I never use etch primer.

 

Right from the PPG tech sheet for DPLF Epoxy.




· Various cleaned and sanded Rigid Plastics:
ABS, Nylon, Polycarbonate, Noryl, PBT SMC,
with DP401LF catalyst only
· Properly cleaned and sanded OE finishes,
NOTE: DPLF must NOT be applied over DPX170 or DPX171.
+ Film build of 1.2 – 1.5 mils of DPLF is required or the surface must be treated with
Metal Cleaner/Conditioner or coated with DX1791/1792.
* Must be cured and sanded
++ Caution: When DPLF is sprayed over lacquer substrates or basecoat that is not crosslinked,
and then allowed to set overnight before applying another coat of primer or a topcoat, lifting can occur. This can be avoided by applying the DPLF Epoxy Primer, color and clear coat in the same day or by adding 5% of DX57 RTS DBC.


DPLF may be applied over:
· K36 PRIMATM Acrylic Urethane Primer Surfacer* · K38 High Build Primer Surfacer *
· K93 Tintable Primer Surfacer Sealer*
· NCS2000 Series Sealers
· Properly cleaned and sanded steel +
· Properly cleaned and sand blasted steel +
· Properly cleaned and sanded galvanized steel +
· Properly cleaned and sanded aluminum +
· Properly cleaned and sanded fiberglass
· Properly cleaned (unsanded) E–Coat
· NCP250 NCT ® Primer Surfacer*
· NCP270/271 Corrosion Resistant Primer*
· NCP272 Tintable Corrosion Resistant Primer* · CONCEPT® (DCC) Acrylic Urethane*
· CONCEPT® (CLV) Acrylic Urethane*
· DELSTAR® (DAR) Acrylic Enamel*
· DELSTAR®/DELTHANE®
for OE lacquer see ++ Caution statement
· DELTRON ® (DBU) Basecoat *
· DF Body Fillers*
· DPX801 Universal Plastics Adhesion Promoter · DX54 ROADGUARD® Chip Resistant Coating · DX Metal Treatments
(DAR/DXR80) Acrylic Enamel*
· DELTRON® 2000 (DBC) Basecoat* ++
· DURACRYL® (DDL) Acrylic Lacquer* ++
· SX1044/SXA1044 High Build Flexible Surfacer · All PPG Clearcoats*
· SX1047 High Build WB Flexible Surfacer
· SX1050 /SXA1050 Plastic Adhesion Promoter
· DX1791 Wash Primer
· DZ KONDAR® Acrylic Primer Surfacers *


 

You are correct, however wash primers are fine. See the above post.

 

So I was pricing out some dp90 with catalyst, and k36 high build with hardner. 2 qts of each, 1 pt of catalyst and 1qt of hardner and it was nearly $400. I about fell out of my chair. Is that normal or am I getting an eye poking from the site I as at.

That is only enough to do the cab and maybe fenders, still would have to do the bed, hood and tail gate, and that isnt even paint, clear, filler, sandpaper and on and on. Plus still need everything media blasted....man I thought I was almost done spending money....