POR 15 prep work

About to try POR 15 for the first time. Does every one use the 3 step process (clean, etch ,paint) or does scuff and paint do a decent job in 1/3 the time?

On new metal, you pretty much have to do the full process. It's not too difficult or lengthly. The etching (just use phosphoric acid from Home Depot) is a spray it on, hose it off process. Your lawn likes the run off from it.

On old metal, you can probably get away with painting right over the surface crust as long as it's not scaling off.

It's old metal. I'll buzz off the surface with a wire wheel and give it a try.

I did just a brush then painted it on over the surface rust. Then 2nd coat. It worked really well.

Descale and brush it on!

Soon to be first timer too with a question: I've got a fabricated steel rear bumper that's looking scabby. Anywhere there was a small chip in the paint, is now bright orange scale. Do I remove all the old remaining paint before applying POR15? I don't think I can just brush it over everything that's already there.

We've only done the full 3-step process. When done per the instructions, results have been as advertised. My ex- is neurotic about following instructions, but I have to admit the parts we did still look perfect nearly 10 years after they were done. The engine she refurbished for her 1800ES still looks incredible.

The one time I did not - just wire-brushed then painted over - rust eventually started coming through again. However, it's an engine hoist that currently lives outside in all weather, so I don't really care (I remove the ram and store it sheltered).

Clif Notes version: If you are doing parts you really care about, don't be lazy.

I've personally found that scuffing up the metal makes a big difference, but I don't typically use their acid etch chemical. IMO you should thoroughly remove any rust present with mechanical means. I have had rust come back with half effort rust removal.

Wire whipped the radiator support in my Impala 2-years ago. I was in a big hurry at the time so I just cleaned the support and brushed the POR-15 on. still looks like it did when I was done (I could have done a better job, but it passes muster).

Good times.

I must've done something wrong. Scraped, brushed, wire wheeled, scuffed, brake cleaned, blew dry, waited a bit, blew dry, applied the POR15, two weeks later much of it just flaked right off again in big sheets.

It's okay, that block was junk, so it was no real loss.

the only spotted where I had issues (did a hood and fender on the mazda) (stripped, wire wheeled, scuffed, wiped down with alcohol, let dry) is where sweat fell onto it during application, there it bubbled up, touching it up was easy though

If you have shiny metal, or strip rust down to shiny metal you need to do the 3 step process. If you are painting over rust (POR) it seems ok to just get the loose stuff off and slap on a few coats.

Knurled wrote: I must've done something wrong. Scraped, brushed, wire wheeled, scuffed, brake cleaned, blew dry, waited a bit, blew dry, applied the POR15, two weeks later much of it just flaked right off again in big sheets. It's okay, that block was junk, so it was no real loss.

The brake clean is where you went wrong. It left a film, preventing the paint from bonding with the metal.

E36 M3, really? I didnt realize brake clean left residue..

What should be used as a cleaner/degreaser then?

I learned the hard way that preperation for any paint system is 90% of the job. I have used POR 15 several times and getting as much rust off as possible will lead to the best job over a period of time.

Etching the metal is also critical. You can use phosphoric acid as someone else mentioned. The metal should be kept wet with whatever you are using to etch until any shiny metal turns dull/gray/black that can't be rubbed off with your finger.

Follow by cleaning and drying (hair dryer/heat gun) and painting with POR 15 as soon as possible. Surprised no one has mentioned not getting it on your hands (nital gloves work)or skin unless you want to wear it for a while.

I use Eastwood's Pre (don't breathe it, nasty stuff) to clean off stuff before using Chassis Saver (POR15's cousin).

As far as I can tell, that E36 M3 sticks to air. I have it stuck on the concrete, stuck on plastic tubes, rubber hoses, oily wrenches, it's frickin incredible.

etifosi wrote:

Knurled wrote: I must've done something wrong. Scraped, brushed, wire wheeled, scuffed, brake cleaned, blew dry, waited a bit, blew dry, applied the POR15, two weeks later much of it just flaked right off again in big sheets. It's okay, that block was junk, so it was no real loss.

The brake clean is where you went wrong. It left a film, preventing the paint from bonding with the metal.

Brake clean shouldn't leave a film. The whole point of brake clean is that it doesn't leave residue the way carb cleaner does.

FWIW, I normally use brake clean as final prep for painting and haven't had issue yet.

Every single time I used brake clean I have fish eyes,since using extra concentrated doses of TSP to final clean no more fish eyes.I have been reading this with interest as I have a surface rusted tercel floor to prep and protect with POR15.

Knurled wrote:

etifosi wrote:

Knurled wrote: I must've done something wrong. Scraped, brushed, wire wheeled, scuffed, brake cleaned, blew dry, waited a bit, blew dry, applied the POR15, two weeks later much of it just flaked right off again in big sheets. It's okay, that block was junk, so it was no real loss.

The brake clean is where you went wrong. It left a film, preventing the paint from bonding with the metal.

Brake clean shouldn't leave a film. The whole point of brake clean is that it doesn't leave residue the way carb cleaner does. FWIW, I normally use brake clean as final prep for painting and haven't had issue yet.

I know brake clean says it doesn't leave a film. The check is in the mail/only the tip/etc.

I'm not a chemist & I know turds (compared to the GRM hive) about paint even though I sold a por competitor for a couple years. I didn't stay at a Holiday Inn Express last night either, but I do know that the only guys who ever complained about adhesion were either the ones who didn't do any cleaning/degreasing or who USED BRAKE CLEAN OR ACETONE OR PAINT THINNER OR LAQUER OR SOMETHING OTHER THAN A WATER-BASED DEGREASER to do the prep.

They all would say that they have always used (whatever) and never had a problem before, which I totally believe. I also believe that it was the source of their problem when using isocyanate POR-type paint, that it DID leave something on the surface that prevented the POR from adhering to the pores of the metal.

Considering every can/bottle had instructions on the label and also printed paper instructions, it kind of surprised me at how many people french fry when they are supposed to pizza and then have a bad time.

The curious thing was that the POR15 flaked off because the rust grew behind it. It adhered very well, but what it adhered to was rust.

FWIW, replacement block was really bad with rust, so I did the same level of prep, but half-assed because this was the fourth block I tried to use and quite frankly I was only painting it because it's harder to do after the engine is assembled and I was actually expecting to find out that this block was bad too, but I didn't want to prove that it was good and then pull it apart again just for paint.

This time I shot it with Krylon Rust Converter, let it stew for 24 hours, then hit it with regular paint. It's been holding up just fine.

I was always led to believe that with POR you didn't want to remove all the rust just descale it. I never had any issues with the areas I did on my truck and the I never heard of any issues from the guy who did the chassis of a 69 vette that I spent three nights degreasing and descaling. I've never used it on shiny new metal or metal where the rust was taken back to shiny metal.