Bare Metal? Which is best? DTM, Epoxy, Urethane, self etch primer, sealer?

in this video I explain the different purposes for most primers out there in the market. The primers include DTM primer , Urethane primer surfacer , high build primer , epoxy primer , primer sealer , self etch aka self etching primer , aerosol primers aka rattle can , krylon , and duplicolor .

If you would like to help support the channel you can do so by using the "Super Thanks" here on YouTube or via Paypal or Cashapp.

Cashapp: $perezjet

Thank you in advance!

[dynamoeffekt]

This video has been the best explaining how to select the right combination. All of the manufacturers' videos are junk. None of them explain the complete procedure and you cannot find any useful information on their website as well. This was very informative. Thanks a bunch.

[BLAZEPSI]

Finally a complete understandable break down.... Thank You!

[dennisoechsle]

Thank you for taking the time to do this video. It was very helpful

[pickleball_tomorrow]

I'm still not 100% certain on the science of these things.. but this is BY FAR the best explanation of the differences I've come across and I highly appreciate you brother.

[deankay]

As an ASE master tech since 1978, I am not a painter but have done 6 or 7 of our own (3 boys) but this was clear information about the way to make you project last. Rock chips to bare metal can spiderweb rust under the paint 6” all directions and I was shocked to see that.
Epoxy to me “Is” the place to start on cleaned, prepped bare metal. Some have a 24 he window while others have 7 days. The ASTM “Salt Spray” test in hours tell you everything. Epoxy is sticking to everything with chemical cross-linking, solvents evaporating with almost a plastic wrap type protection. At 6’ 3” and big hands, spend the $6 for a rattle can spray handle. It makes it so easy to control, overlap and speed because your thumb is not changing best practices for applying a finish, even if it’s under the vehicle. With practice, 10% quaility urethane reducer added to an epoxy product makes a smooth sealer. I prefer the word primer not even be on the can but it is. As always, follow manufacturers product sheets and measure properly using good overlap and your base will stick to epoxy, epoxy sticks to your paint ready project. Now a rock chip may not flake off as easy.
Son, I subscribed and liked what I heard. You will do well and some side-by-side destruction test panels. That will get attention. I too don’t care for DTM coatings because I have seen the feathered edges of primer and filler lift & curl as the acid eats into it. That kills your day! Thanks for the information!

[tsmg]

Here's PPGs definition of "properly prepared"

What Does "Properly Prepared Bare Metal" Mean?


In many of our product data sheets, you may notice this or a similar statement under the Compatible Surfaces or Substrates section:

“May be applied over properly prepared and treated bare metal”. But what does this mean?

This means that your bare metal substrate must be properly sanded and treated with an appropriate direct-to-metal product such as an SX metal treatment, etch primer, or epoxy primer prior to applying anything else. These coatings insure adhesion for subsequent layers over the bare metal as well as provide additional corrosion protection.

This step is especially important when using urethane primers or sealers. Their chemistry typically does not provide adhesion to bare metal – they must only be used over treated bare metal to insure optimum adhesion. So if you happen to sand through to metal, apply a bit of etch primer to insure it sticks!



If you sandblast or aggressively sand steel panels you remove the phosphate coating, which is the first step to protect steel from rusting. There are 2 basic ways to replace the phosphate coating: metal prep/acid wash--and--self etching primer. Epoxy primers do not convert or stop rust chemically, and most of the popular epoxy primers have little film build, long cure times and can absorb moisture and solvent--PLUS--most epoxy primer tech sheets recommend treating the metal with metal prep/acid wash for the best corrosion protection. Over the last 50 years, lead, zinc and chromate have been removed by law from paints. These are heavy molecules added to paints to protect from Ultra Violet, chemicals and moisture. The acid in metal prep (phosphoric acid) can affect the hardner part of epoxy primers causing them to air dry but not cure partially or completely. This is why most epoxy primer tech sheets recommend completely neutralizing the acid/metal prep before applying epoxy primer. Epoxy primers have been "sales promoted" pretty heavily in the last 50 years. I remember PPG/Ditzler promoting their DP40 primers with "Just DP it and Forget it", but that was back when DP epoxy primer actually had lead in it and they kept on promoting it because they knew regulations were already removing lead from paint products. Now they are selling DPLF (lead free) epoxy primer. Back then, if I needed to use epoxy (on restorations) I used DPU 35 epoxy (from their aircraft and industrial line) which had 3 times the film build and cured at least 3 times faster-and contained lead. We used metal prep on rusty steel first, and then the DPU35-per PPG tech sheets. Today, I see PPG has some really nice high build epoxy primers (again from their industrial products) that are becoming popular for high end restorations--VP2050 and CRE-X21--of course lead and chromate free. These are quite expensive and still are recommended over properly treated steel (metal conditioner).

For the "informed" hobbyist, I recommend the following on sandblasted steel:
1)Sandblast- carefully to avoid warping.
2)DA sand the sandblasted steel with 180 or 80 grit to soften the blast profile/texture. This helps keep the acid in self etching primer from being trapped in the texture (sandblast profile)--watch out not to apply too heavy of a coat.
3)prime the steel with a "mild" self etching primer (chemical adhesion) followed by at least 2 coats of hi-build 2K urethane primer. This (self etch) will neutralize rust in the pores of the sandblasted steel and the (2K) will add a moisture proof layer to protect during storage.
4) When you are ready to do rust repair or filler, you can cut out the replacement areas and repair/weld and do body filler either by grinding off the primer before filler or sanding the(good quality) 2K and applying filler on it (mechanical adhesion). I prefer filler on bare steel, but good fillers will adhere to good cured 2K. If you do either way, remember to sand far enough out on the areas to reprime (over filler) so you have good adhesion. Also if you apply the reprime 2K too heavy, the solvents can lift/wrinkle your filler edge.


Etch primer
There are 2 basic etch primers-

VINYL WASH primer-has more etching capability but no film thickness or build. It needs to be topcoated with a fill primer or sealer and then paint. This type of etch primer should NOT be put over Bondo. It is for bare metal only.

MILD ETCH PRIMER WITH SOLIDS-has a milder etch and some fill. It CAN be applied over Bondo. Vari-prime (DUPONT), Wash primer EM (SIKKENS AKSO/NOBEL) are a couple of names that come to mind. This can also be topcoated with a filler primer or primer sealer or directly with paint (industrial application.)
You have to check and see what system/brand you are going to use and then get the technical info on the application requirements and read and follow the manufacturers instructions.
DO NOT use metal prep before applying etch primer-it needs just a microscopic amount of oxidation to bond with. The phosphoric acid in the etch primer is usually less than 2.5% (by volume) but that bonds with Iron oxide (rust) to form Iron phosphate which is the etching/phosphatiing process. Removing all the rust with metal prep/conditioner (phosphoric acid) will leave nothing for the primer to bond to and can lead to peeling.

These systems usually go as follows:

Vinyl wash primer-1 medium wet coat (.5 mil) over clean, dry, sanded/sandblasted bare metal. You can see through this coat-its very transparent (vinyl resin). This followed-probably within 30 minutes (wet on wet-no sanding) by a good catalyzed 2 part filler primer for filling and sanding (5-20 mils). Or in straight refinish (trailers/industrial) applications-vinyl wash primer followed wet on wet by a non-sanding primer sealer(1.5-3 mils)-followed by paint.

With the milder etch primer you prepare the metal the same-do your bondo work then clean and apply the milder etchprimer (1-2 mils) followed wet on wet/no sanding (probably within 30 minutes- read the tech sheet for the product) by a good catalyzed 2 part filler primer for sanding and blocking.

For project cars I usually rough out the metal-do my filler work on the large areas then use the mild etch primer followed by 2 part filler primer. Then for smaller areas I can use the spot filler/ catalyzed glazing putty over the sanded filler primer to smooth out small imperfections. I will probably reprime areas that need more fill and block sanding-then on to paint.
If it is going to sit for as while, I prep the steel-then etch prime (either one) followed by good 2 part filler primer. Then when I'm ready for bondo work, I just hit the repair area with a grinder to bare metal and do my bondo work followed by the filler primer.

Epoxy primers DO NOT etch the metal. They bond by mechanical adhesion. There are many different epoxies for specific applications. You need to research what will do the job for your intended purpose for which ever primer/paint system you are going to use.

The acid in etching primers can cause the epoxy primer catalyst/hardner to change chemically and not cure or possibly fail/peel.

The acid in etch primers slows down the catalytic reaction of the hardner in Bondo/body filler (polyester resin-catalyst MEK peroxide). If you put bondo over etch primer and there is still a minute amount of residual acid-you could have a failure/loss of adhesion etc.

The amount of acid is very minimal in these primers. It is mixed with a solvent to reduce/thin the primer. If the etch primer is not fully dry and cured there COULD BE be residual acid/solvent in the primer film which could cause the reactions described above. Self etching primers/wash primers, typically have about 5% phosphoric acid (the etch part) in the hardner/reducer that is mixed 1 to 1 with the primer. This makes the acid content of the mixed primer around 2.5%. Acid is always converting with other substances/compounds like the iron oxide in the steel and the solids part of the etch primer or even the compounds in the 2K primer applied over the etch primer. Eventually all the acid will convert and become non-acid compounds. If your etch primer is applied too heavy it can trap solvents in the film which contain a small amount of acid. There is no real accurate way to know the acid content remaining in a heavy application, so it is best to manage your application to avoid this--don't pound it on!--and be VERY CAREFUL in cold shop conditions, as cold panels and air temperature will slow solvent evaporation and the cure of products with a catalyst/hardner.

Self etch primer followed by a good 2K primer is an excellent system/foundation for restoration and custom work and you can shop for products that have good quality and price. It also makes an excellent storage coating for projects that won't be completed soon and is still compatible with almost all of the paint systems available for automotive refinish.

[wingrider]

Great presentation. I was wondering how to approach my 1972 Ford Gran Torino Sport diff and this answered all of my questions. Best breakdown I have seen. Good job.

[Marine-]

Thank you!! I am in the process of restoring my 1947 John Deere B tractor and your video was very helpful. Impressed enough to SUBSCRIBE.

[aaronwlkr]

Good video. I think a lot of people that try 1k rattle can epoxy, don't clean well then do a dust coat, before they pile it on. Rattle cans are tricky, you got to really shake them up good. It also helps to put them in warm water to warm up the paint a little IMO. If your can has been hitting in doors and the paint is say 72 degrees, its not going to flow as well as a can that is say 85deg.

[frankammirati]

And this what makes PPG DP90 so popular in the industry, it’s literally 2 products in one deposing on how you mix it, as dtm or as a sealer, just buy the additive to make it sealer and done .

[rsonweb]

I keep coming back to this video as I do my 63 Biscayne. Good video with great information - Thanks!

[splash]

Some good info here, but some misinformation aswell...
Most self etch primers do not need to be primed over top. You can top coat most self etch primers after they flash off. I use RM self etch everyday in my paint booth. It is used over burn throughs in paint or primer, prior to painting.
Also you do not have to use sealer over most primers. You can paint over sanded urethane primer. Sealer is used to create a uniform surface when panels are spot primed or when a certain colour needs a ground coat.
I believe the only exceptions are when you prime with a polyester primer, then it needs to be sealed with primer sealer or urethane primer applied over the polyester.
The other times we use sealer is when painting bare plastic bumpers and other parts. But the sealer must contain adhesion promoters.

[boxoftj]

100% support your statement about the all in one primer paint. I used to use that to cover rusted spots on frame and suspension of my semi. Even w when cleaning all the rust, rust came through, which is exactly why I'm here learning about primer

[danstoops]

I’ve been searching YouTube for weeks, trying to research about primers, and everything I’ve been wanting to know, is mostly in your video! Thank you! I wish you would do one on aluminum now,
LOL

[taylorh]

I lay paint down overtop off self etching primer. When I did my 98 I D/A sanded it all down did all the bodywork laid down three coats of Pro Forum self etching primer blocked the primer each coat then went directly to paint this is how I do all my projects and I've yet to have a problem did my 98 years ago still looks great.

[eugeneirons]

Thanks a million, I am working on my Avenger and needed a little guidance and you provide that and more

[jamescon]

Yeah, it's pretty hard to beat a good quality Epoxy 👍

[beatrizjimenez]

I'm currently restoring my 2004 GT. Thank you for the valuable information!!!

[lestatdelioncourt]

Ive been needing all this info in one place for so long! thank you so much for sharing your knowledge and helping people with their projects

[aliposhtpazan]

God bless you for all your useful information about priming. Many beginers get confused what chose and when. Many thanks for your experience and explanations