Can I use POR 15 after I preped and sprayed the SEM rust-conversion? Wish I just went with POR.

 

I'm not familiar with the SEM converter. If it left the surface porous and rough, then I'd say go ahead. Otherwise, I wouldn't. POR15 designed to be applied directly to a rusty surface.

Eastwood has a multi-step process that starts with a converter, then top coats with a 2nd product. You might take a look at that.

 

I second what DynoDave said. POR15 is designed to be applied to rusty surfaces.

I won't use POR15 on anything except heavily pitted, rusty surfaces. I once coated the entire engine bay and front frame of my Camaro with POR15. I followed the directions and scuffed everything up with coarse sandpaper since the car had no rust. It looked okay, but after it dried completely I went to wash it and the POR15 flaked right off. It basically won't adhere properly to anything except heavily rusted surfaces. I thought I could use it as a preventative measure, but it doesn't work that way at all.

If you spray a high quality clear coat over your SEM it will probably be good. Good clear coat basically seals the surface from oxygen (rust can't form without oxygen). I have a rusty piece of metal sitting outside my garage in the sun and weather. Years ago I tried several different paints on it to see how well they stopped the rust, even when exposed to weather 24/7. The rusty section that I applied clear coat directly over looks exactly the same as I sprayed it years ago. You can see the rusty surface through the clear coat but no rust has come through the paint or spread.

 

If you buy the POR kit you get a metal prep solution that neutralizes rust, so yes, you should be fine putting the POR over the SEM converter. Most people just buy the paint and have no idea that there are actually other steps you should follow before painting over the rust. I would also use the POR over the "converted" rust, it just doesn't stick to shiny metal

 

I have used the SEM on surface rusted areas in my iroc and not had any issues at all.

 

Prepped my engine for por 15 and all but the machined head faces are good after probably 10 yearsI did follow all procedures and used all 3 steps
I used a 3M abrasive wheel (or 25) to remove the paint from the engine compartment, then sprayed it with two coats of Zero Rust. That has held up for just as long, but gave a nice satin finish to the engine compartment.
Warning, Zero Rust in spray cans will buzz you into being a bad painter before you're done!
I still have some touchups to do. (the car and I were separated for several years)

 

I did most of the underside of my car with POR15 AFTER taking it down TO BARE METAL. smooth, bare, clean metal. this was about 8 years ago (winter 2010). it is still absolutley perfect. not one single flake, chip, pit or anything. I followed their directions in that I used the prep-spray product they sell.

here are some photos of it http://www.freewebs.com/iroczman15/2010.htm

it still looks magnificent, although the back color did fade slightly.

you can do it. It is designed to work great on rusty surfaces, but I can attest if you prep it correctly, a smooth surface will work just fine too.