Epoxy Primer Trial Failure

arbezc

New Member
Hello,

I'm new to this forum. Being retired, I now have time to get back into a restoration that's been stalled for many years. The car is a 1973 Porsche 911 that been stripped to a bare shell. I plan to first work on the under body & epoxy prime as I go.

In November I created a test panel using various epoxies on a sheet of mild steel. (See below) Each 2"x2" section is separated by a band of bare metal. In each case I followed the manufacturer’s instructions. The steel was cleaned & etched using DuPont M3 Cleaner & 224S Conditioner using a Red Scotchbrite pad. The paints, metal & room temperature were all above 70F. The SPI Epoxy was induced for 2 hours before spraying. The panel was “aged" indoors for two weeks before mounting on the front of my wife’s car. The car is only driven intermittently but our conditions are severe with lots of rain, snow & salt.

The SPI Epoxy panels were added in December and are the two outer most vertical columns. Metal prep varies from top to bottom: the top row is bare metal, the second has Zinc primer & the bottom is PPG etch primer. Four different epoxies were sprayed on top of these coatings. Each test section was scratched with an “X” mark using a scribe to test how well the primers resist corrosion when damaged.

2021.1.10 Pressure Rinsed (Small).jpg


They all looked fine until the car was pressure rinsed at local facility a few days ago. The SPI Epoxy began lifting under the pressure washer. (See the top right & left panels) There was some lifting on a couple of the other sections. Can you suggest what may have caused this?
Any comments or pointers are welcomed,
Thanks,
Charles
 

Chris_Hamilton

Trying to be the best me, I can be
You take the time to do all that but can't read the instructions???? Any acid etch/metal conditioner type product must be properly neutralized before applying epoxy. Only use an acid rust removal product when it is absolutely required and no other options exist. Clean steel does not need it. All clean steel needs is 80 grit DA sand scratches. Ideally you don't ever want to use it (acid) on something you are coating with an epoxy, but it can be used if properly neutralized. Epoxy will not stick to an acid film.

In a nutshell to neutralize you would re-wet the panel you treated with metal conditioner with more of the product. Keep it wet with the product (do no let it dry) for 15-30 minutes. Emphasize that you have to keep the panel wet with the product. Do not let it dry. You can scrub with a scotchbrite if you want too. Then simply rinse very well with water. Blow dry. The panel is now neutralized. Any acid product has to be neutralized or failure will occur.

From the SPI Tech Manual. Included with every order. (it is also on the can)

"Precautions:
NEVER use SPI Epoxy over a Soda Blasted vehicle unless you call us first for proper neutralizing instructions.
NEVER use SPI Epoxy over Acid Etch/Wash Primers or Rust Converters. It will not work and we strongly suggest if you want to use a rust converter that you use the rust converters paint system instead of SPI.
Acid treatments should not be used unless you know the proper way to neutralize them, again call us first to be safe. Acid films can cause an adhesion loss.
We only recommend using Ospho’s acid treatment if you even need one.
If not handled properly these issues can destroy a paint job and will result in an expensive mistake.
For bare metal or aluminum do NOT use any other cleaner except 700-1 for cleaning."
 
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arbezc

New Member
Thanks for your responses & recaps of the procedures. I started the trial before discovering SPI products. Yes, I've read the instructions but wanted to standardize the process across all epoxies being tested. I'll try to explain better:

Etch Primer:
Only the lower two rows of the test panel had an etch primer applied. The uppermost row was only treated with a metal cleaner & metal conditioner. The panel was kept wet the entire time, as is standard practice. Afterwards the whole panel was neutralized in clean water & thoroughly dried.

Sanding:
Sanding with 80 grit paper would provide much better adhesion than red Scotchbrite. However, started with Scotchbrite & wanted to create worse case for all the samples. I'm hoping to accelerate the results by creating a worse case condition.

My Process:
The entire upper row of 4 epoxies was prepped the same way & did not involve etch primer. I'm still perplexed as to why only the SPI Epoxy lifted during pressure washing. I'm sure I mixed the material correctly; it’s hard to mess up a 1:1 ratio. I didn't add any solvents. It digested for 2 hours; it was sprayed at over 75F (checked with a temperature meter) & allowed to cure for 2 weeks before mounting. I applied 3 wet coats with a flash time of 1 hour between each. My thickness gauge read 3.1-3.4 mils. The SPI test sections were glossy & hard. During the scratch test the SPI seemed very tough & showed no chipping - I was impressed.

I've been using this process for many years & have never had a paint (including aerosols) lift off so easily. A similiar test was done last year with different materials. I suppose I could start over again, but what to change?

Any further ideas are welcomed,
Thanks
 

texasking

Promoted Users
In each case I followed the manufacturer’s instructions.
No, you didn't. Even PPG does not recommend epoxy over etch primer. SPI's instructions for epoxy prep could not be more clear. Follow these instructions to the letter, and you literally can't beat it off with a hammer. Any deviation from the instructions will cause it (and any other product) to fail. If you want a true test, follow each manufacturers instructions to the letter instead of introducing variables that have been known to fail. The only 3 things that would cause that is an acid film (probable), an insufficient scratch, or metal that is not cleaned properly, or with the wrong product.
 
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arbezc

New Member
Sorry I wasn't clear. The PPG epoxy I'm using is Aquapon an industrial primer. It’s designed to work over a thin layer of PPG Polyclutch wash primer. PPG's instructions specifically recommend this combination. It’s true, PPG automotive primers stated not to use an etch primer starting in 2014.

In any case, etch primer was not used on the test patches in question. I could run the test again using SPI process (sand with 80 grit & no conditioner) but I'm still perplexed as to why none of the other primers came loose.
 

arbezc

New Member
I was following a process used for many years. It's pretty standard across most primers. The main panel was already painted & mounted before I decided to attach the SPI panels on the outside. I was hoping to test the products using a common approach.

It appears that SPI's Epoxy primer needs to be applied in a different way. The primer itself seemed very tough. I wonder if a sudden change to cold temperatures affected it? The SPI panels cured at room temperature for 8 days. Also the SPI primer was mixed about a month ago and the remainder is still fluid whereas the others have hardened. The garage is at about 40F.

I was hoping to identify a reason for the difference in outcomes. In any case, thanks for your feed-back, you've helped confirm the SPI process.
 

crashtech

Combo Man
Hi arbezc, and welcome to the forum! I think we can help get you on the right track if you'd like to prepare and spray another set of test panels. First, would you be willing to read the entire entry on epoxy primer in the SPI Tech Manual? It starts on page 11 and runs through page 14, there's a link to the manual in my sig. That way, we can begin to address the proper technique for application which does vary from other primers in that it is more simple, but can be a little unforgiving about things like proper surface temps.
 

Chris_Hamilton

Trying to be the best me, I can be
You sound like an intelligent man. I think you are overthinking this whole process. My Dad used to love to refer to the K.I.S.S. principle. You should do that here. If you use SPI Epoxy, follow the instructions to a "T", then you will not have issues. It is the finest automotive epoxy on the market today. Bar none. But it needs to be applied correctly and just as important, allowed to cure correctly.

All primers are not created equal. One manufacturers products are not the same as another. There is no standardization in this industry. Industrial procedures don't really apply to automotive refinish products. Especially in 2021.
And for any product you are using there is something called the Technical Data Sheet. All you have to do to find the TDS of a specific product is google the name of the product and "TDS". Making assumptions will only cause you grief.

SPI does not have specific TDS's but all the technical data you need to know is included in the Tech Manual. Read it please.
 

Chris_Hamilton

Trying to be the best me, I can be
Sorry I wasn't clear. The PPG epoxy I'm using is Aquapon an industrial primer. It’s designed to work over a thin layer of PPG Polyclutch wash primer. PPG's instructions specifically recommend this combination. It’s true, PPG automotive primers stated not to use an etch primer starting in 2014.

In any case, etch primer was not used on the test patches in question. I could run the test again using SPI process (sand with 80 grit & no conditioner) but I'm still perplexed as to why none of the other primers came loose.
You stated in your first post the Dupont 224S Metal conditioner was used. That is the reason for the epoxy failure. It is an acid based product that if not neutralized correctly leaves an acid film on the metal. SPI Epoxy will not bond with an acid film. Refer to my first post for how to neutralize an acid product like this.

And again I will emphasize with clean steel there is absolutely ZERO need for any metal conditioner type product. None whatsoever. 80 grit DA scratches are all that is required for Epoxy to adhere correctly to steel. As for rusty areas there are far better options than using an acid product.
 

texasking

Promoted Users
The SPI panels cured at room temperature for 8 days. Also the SPI primer was mixed about a month ago and the remainder is still fluid whereas the others have hardened. The garage is at about 40F.
That is concerning. After 8 days at room temperature, the remainder should not be fluid, unless the room temperature is 40F. Even after 24hrs. at 65F and then colder temperatures, the remainder should be firm but flexible after that amount of time.
 

crashtech

Combo Man
The thing about room temperature is that in the winter especially, a comfortable feeling room can have panel temps in the high 50's. So there could be a number of problems, which is why I encouraged a re-reading of the epoxy tech sheet. It really does have everything you need to know, but some of the most important stuff is right at the end.
 

Chris_Hamilton

Trying to be the best me, I can be
Metal temperature (not air temps) needs to be at a absolute bare minimum 65 degrees, (70 is preferred) for 24 hours. Primer needs to be at that temperature as well before spraying. The chemical reaction that occurs (curing) essentially stops once epoxy goes below 55-60 degrees. All this is covered in the Tech Manual.
 

arbezc

New Member
Thanks for all your suggestions, much appreciated.

A hard copy of the Tech Manual shipped with the primer. I’ve read the recommended pages & made notes before preparation & painting. I follow the TDS sheets for all materials used. The SPI spray-outs were done later. To maintain a common base line I deviated from some of the SPI recommendations. I didn’t think the changes were significant.

Each panel was cleaned & conditioned with DuPont materials. I was careful to thoroughly rinse & scrub the surfaces before drying as their TDS states. I purposely did not degrease the panels with Lacquer Thinner following the warnings in the SPI instructions.

At the time of spraying the SPI samples my garage would have been sitting at about 60F. However, I ran a 240V unit heater directly on the product & panels for a good 30 minutes. My infrared thermometer showed around 80F on the panels just before spraying. The panels were left in this condition for about 2 hours before being moved into the house which is kept at about 70F. The samples were kept indoors for 8 days before mounting on the vehicle. Outside temperatures in December ranged from about 23 to 50F.

The left over paint was left in the garage which ranged between about 30-50F without heat. I’m surprised that the SPI Epoxy has thickened but remains fluid even at these temperatures. The other 3 Epoxies cured at different times but were set-up within a week. It appears that SPI Epoxy is very sensitive to temperatures. However, I controlled the environment within the rules laid out in the Tech Manual.

I’ll forward a couple of close-ups for clarity:

The paint in each column (L to R) is: 1. SPI Epoxy, 2. Corlar Zinc Chromate Epoxy & 3. PPG Aquapon Epoxy
The metal prep in each Row (Top to Bottom) is:
  • DuPont M3 Cleaner & 224S Conditioner
  • The above + Wurth Zinc Spray Light
  • The above + PPG Polyclutch Wash Primer
SPI, Corlar & Aquapon Comparison - 1.14.2021.jpg


Strangely the SPI is performing better over the Etch Wash Primer & Zinc Spray. (The bottom most section)

SPI Close-up 1.14.2021.jpg


The use of a layer of Zinc under Epoxy Paint is common in Industrial applications. It’s called a “Duplex Coating”. The intention is to retard corrosion if the outer layer is damaged. I realize this is likely overkill for a collector car. I had planned to follow this approach only for the underside & suspension. Standard materials need to be used on the outer body to match the OEM finish. The car was originally painted in Base / Clear.

My take-away’s for a follow-up SPI trial are:
  • Don’t use any metal conditioner (I’ll need the SPI Cleaner)
  • Scratch surface with #80 grip (This sounds like a good idea for any base coat)
  • Maintain above 70F for all materials for 1 week (which I believe I did)
Thanks again for your ideas,
Charles
 

Raymond_B

Hobbyist
I like your attention to detail, but it seems you keep going back to saying things like "common practice" or "industry standard". I think you should resist doing anything other than following the SPI doc verbatim, literally no other products or procedures no matter how you've learned or researched it previously. I am also impressed that you talked your wife in to driving around with that hootus on the front of her car :)
 

Chris_Hamilton

Trying to be the best me, I can be

This car was restored using SPI Epoxy. If it was good enough for this car it is good enough for any car including your 911. :)

2015 Peeble Beach Concourse Best of Show
 
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