[dpoltzer]

Stripping my car to bare metal and want to prime it before starting Body work. Is Urethane ok to use or is epoxy better. Already stripped doors and deck lid and used Urethane primer on them, is it ok to use epoxy on rest of the car? Thanks.

[dhutton]

Always epoxy on bare metal. Urethane on bare metal is cheap collision work. Do your filler work in the epoxy recoat window for best adhesion.

Don

[HoovDaddy]

Another vote for epoxy. For the past 20 years I've been applying epoxy after all the metal work (welding and lead) has been completed. I wash the metal with acid, then apply PPG DPLF. DPLF provides a very durable base. Then I switch to Southern Polyurethanes epoxy for all the block sanding and the final sealer. Body filler can be applied up to 7 days without sanding. DPLF is okay to apply over the acid etched metal, SPI epoxy won't work over the acid prep. SPI is cheaper and sands better than DPLF, but still high quality.

I found that using one single product for all the blocking and sealer saves cost, waste and eliminates incompatibility issues. Open shelf life of the SPI activator is longer than PPG. I also recommend the SPI waterborne wax and grease remover.

[nytrainer]

To add to others advice I would remove the urethane primer (even if it was labeled direct to metal) you applied to bare metal, sand bare metal with 80 grit and apply epoxy.
As mentioned you can apply filler within the 7 days without sanding epoxy but if you’re doing the body work over time you can follow their directions (SPI epoxy).
“You have 7 days to apply 2k Primer or body filler over epoxy without sanding first.
Between 7 and 30 days it must be sanded with 180 grit first.
After 30 days the epoxy must be sanded with 180 grit and reapplied before applying another coating over the epoxy primer.”

[dpoltzer]

Epoxy it will be then! Thanks for the great advice.

Dave

[carcrazy]

I've always used PPG DP on bare metal and then followed up with K36 within the 7 day window. The K36 sands well....DP not so much.

[dhutton]

SPI epoxy sands nice and coats a lot less than DP….

Don

[tjs72lemans]

I will have to say, the last primer I used was SPI and was surprised how well it sanded and didn't plug up the sand paper.

[Entropy11]

Another vote for SPI Epoxy. Can’t say enough good things about it.

https://www.southernpolyurethanes.com/epoxy-primer

[HoovDaddy]

In my experience, DPLF is more durable as the first substrate because it allows the use of acid to pre-wash and etch the metal. SPI won't go over acid prepped metal according to the data sheets. I switch to SPI after 2 coats of DPLF have been blocked.

Transtar also has an epoxy primer I've used over DPLF that performs exactly like SPI and it is usually available at paint stores.

To be a believer in how well DPLF adheres, spray both products on a test panel and beat on it.

[flat-bill]

What about this stuff?

http://products.axaltacs.com/dcat/us...l?desktop=true

[HoovDaddy]

Originally Posted by flat-bill

What about this stuff?

http://products.axaltacs.com/dcat/us...l?desktop=true

Have not used it, Nason has good products, I use PPG because the store is closer to me. The data sheet for the link you posted notes that "For the ultimate corrosion protection prime bare metal areas with Ful-Poxy® 491-10™" so in my opinion this product is a good primer to apply over epoxy so you can get the corrosion advantages of epoxy. And as a sealer it comes in black, gray and white. I always use a test panel in the sun with black and white as a base to see which way a final color looks best.

Nason also makes DTM Epoxy Primer/Sealer as well so you would get the adhesion and corrosion protection from a Nason epoxy. The data sheet does not mention acid compatibility, but Nason sells acid wipes, so I assume they are compatible and are quite handy compared to the liquid style.

By using epoxy throughout the entire process from coating the bare metal through to the sealer, you have the advantage of applying filler over the epoxy at any stage. You can't put filler over most 2k primers.

[dhutton]

Originally Posted by flat-bill

What about this stuff?

http://products.axaltacs.com/dcat/us...l?desktop=true

2K urethane on bare metal is fine for low end collision work but has no place in restoration work imho.

Don

[Entropy11]

Originally Posted by HoovDaddy

SPI won't go over acid prepped metal according to the data sheets.

My link in the post up above leads to the tech bulletin at the bottom of the page.

(Re: SPI Epoxy Primer)

“Ospho is the only rust treatment we recommend IF needed under epoxy primer. Apply Ospho as needed and leave it on as long as you like.
When you are ready to neutralize the dry Ospho, apply one more coat of Ospho over the area to be neutralized and let it set for 5 minutes.
Using a clean towel and water, wash off the wet Ospho like you are washing a car then dry with a clean towel.
A dry acid film cannot be neutralized or sanded off.”

Not trying to push SPI products… just listing what they say about acid treatment. There are countless “quality” epoxy primers on the market, this one just happens to have some unique qualities that many of the others lack. Just my take on it.

[HoovDaddy]

Originally Posted by Entropy11

Just my take on it.

Ospho is a rust inhibitor, different kind of product.

The acid I'm referring to is PPG TX. It conditions the metal for application of DPLF epoxy primer as well as deep cleaning small rust pits.

Not compatible with SPI primer. Thats why I apply DPLF first, then change over to the less expensive SPI for all the blocking and the final sealer.

[dhutton]

Originally Posted by HoovDaddy

Ospho is a rust inhibitor, different kind of product.

The acid I'm referring to is PPG TX. It conditions the metal for application of DPLF epoxy primer as well as deep cleaning small rust pits.

Not compatible with SPI primer. Thats why I apply DPLF first, then change over to the less expensive SPI for all the blocking and the final sealer.

OSPHO is a balanced formula of Phosphoric acid, Sodium Dichromate, Surfactants, and Extenders.

Are you referring to PPG DX rather than TX? It is also phosphoric acid based.

What sort of testing are you basing your claims of adhesion of DPLF versus SPI epoxy? Why are you opposed to neutralizing the acid film per SPI recommendations? Any test data to support your position?

Don

[HoovDaddy]

I was referring to DX products. Product compatibility is everything in the paint world. I would check with a PPG rep before using Opsho or with the rep of the brand of paint you plan to use. I'm not saying Opsho won't work, but I don't like using hardware store products on automobiles. Paint is expensiv, I won't risk failure during the project.

DX 579 is the product I wash bare metal, welds and lead with, I've used it since 1969. It deep cleans and neutralizes any small rust pits and etches the metal. If rinsed with hot water the metal stays gray, if rinsed with cold water it turns gold as shown below. It can be primed without any further prep. Or 579 can be followed up with DX 520 which is a phosphate coating that will improve adhesion, but it's not required. DX 520 is not compatible with lead, so I seldom use it because I use lead whenever possible.

My adhesion claims as stated prior, are from a test panel many years ago. The whole panel was 80 grit. One side was DX 579 and PPG DPLF the other side was SPI Waterborne Wax and Grease Remover followed by SPI Epoxy primer. After 1 week I used a sharp chisel to scrape the paint off and I hit the chisel with a hammer. Both adhered well, but I could dig into the SPI easier.

I still use SPI on every car we do, I just don't use it over metal or fiberglass. Personal preference.

Same goes for SPI Clear. It's great for show cars, easy to sand, super high gloss, we use it on almost every classic we do for the past 20+ years. But I won't use it for daily drivers or classics that are regularly exposed to road hazzards because it's easily scratched or damaged compared to PPG Concept. PPG Concept Clear is more durable in my opinion.

Every painter has their own ways. I've been building cars for over 50 years and I have kept up with the changes. Some paint jobs in our club are hitting 22 years now and still look great. This is just the way I do it, and it works.

[dhutton]

I think you would have gotten a different adhesion result if you had put the test panel in the sun for a day or two.

Don

[nytrainer]

If your procedure works for you Hoov that’s great. No one’s trying to change your mind. I used the DP epoxy in the past (prior to the lead free version) but then I discovered SPI.
Ospho which is also a phosphorus acid formula (just like the DX 520 and DX 579) and is easy to use, stores well, works great and is compatible (assuming it’s neutralized). Way easier for me to have one epoxy/sealer that is easy to sand, less expensive, stores well, etc.
When someone who is unfamiliar with the process and looking for advice I try to steer them to what’s easiest to understand, less costly and I know from experience works well.

[Entropy11]

I think the exchange of information is what’s great about this site. Other sites or FB groups get crazy, but here things tend to stay on point. I’m glad you elaborated Hoov, I use SPI for many reasons that suit me and my needs, but I’m always eager to hear what other people are sold on or have been sold on for years. It’s also great to see people differentiate their products based on “show” vs “driver” needs, and hear their reasons why. Thanks.

Curious if the chisel test with SPI would have been different with more than a week cure (or possibly sunlight like Don mentioned).