POR 15 verses Epoxy Primer

Duane WI

Member
I have been trying to figure out the advantages of POR 15 over epoxy primer. The direction for POR 15 are, remove all loose rust (typically done with wire wheel on angle grinder), clean metal with a grease / oil remover, treat metal with acid solution, let dry and then apply POR 15. You are supposed to use the metal cleaner and acid solution provided by POR 15. If you do the exact same steps but use epoxy primer won't the results be pretty much the same? Both POR 15 and epoxy primer are supposed to have superior adhesion properties and seal the metal. I have some areas on the floor of my 52 Chevy pickup project and I don't want to spend the efforts to remove all of the rust. I have it wire wheeled really good right now and trying to decide epoxy or POR 15. Either way I know it won't be a perfect solution but all of this is covered by the seat or carpet. A few rust spots working through the paint over the next 5 or 10 years isn't a big deal. I can clean and retreat them when it happens. I use Omni epoxy primer which works fine over phosphoric acid metal prep solutions. I know some epoxy primers are not compatible with acid metal prep solutions. I already have a can of epoxy primer and will be shooting the truck anyway. Seems like using POR 15 is just an extra step and expense.

On a side note my first pickup truck project was completed about 6-7 years ago. I took the frame and wire wheeled it, pressure washed it down with Simple Green, hit it with phosphoric acid, rinsed it off, let it dry and painted it with Rustoleum. So far this is holding up well. I also did something similar on the underside of the fenders and hood. Also holding up well.
 
Hi. I am working on 1941 GMC and a 1950 Chevy Suburban - similar to your truck. POR is a moisture activated single stage urethane type of finish. I have used it and had some good results and some not so good results. IMHO surface prep is key and how and where this finish is used. If applied too thick, it will readily chip off from the prepped metal. I found that if it is applied on a surface that flexes, it may chip off or peel. Yes. Follow their procedures with the metal cleaning and metal ready (zinc phosphate) to give you the best chance for adhesion. The finish is unique, and good luck hand sanding it after it cures. It is tough. I use it in areas such as overlapping metal joints, welded seams such as behind a seat, under a gas tank, or the interior cab corners (lower ends), where water, moisture and grit will tend to settle or not dry too fast.

I chose to avoid POR for the cab interior and main floor and went with the two part epoxy primer. Seems like it would be easier to repair and prep for paint if needed. Of course, its a floor...not a fine piece of furniture, and a floor mat, sound deadening or insulation material, and a carpet will cover it up and help protect it. But grit and moisture tends to work its way under and does over time abrade the surface.

Both finishes should help seal and you cant go wrong. But, if POR is used as a short cut to minimize the time and effort to treat rust, you may find that over time the rust will still pop through the POR as I have experienced. Seems like for longevity sake, there are not short cuts to a quality finish - and removing rust is key no matter what product is used.
 
Thanks for the experienced based information. I am thinking that POR 15 really doesn't add much value over epoxy primer. Your input seems to support that line of thinking. Any metal that is readily seen like the dashboard, rear of cab above seat, door frames and exterior I remove all of the rust and treat the pits with phosphoric acid. It is the floors, inside firewall and behind the seat areas that are going to be covered with carpet or sound deadening material that I want to shortcut the full rust removal. Thanks again.
 
The problem with bed liner is it holds dirt and is hard to clean. I have used it to undercoat fenders and cab bottom. Tough stuff.
 
Epoxy primer is not designed to , and will not, stop or neutralize existing rust or scale. It must be applied to CLEAN surface. What it DOES do is prevent rust from forming and creates the perfect base for top coat. It will stop rust from permeating where a stone chip or scratch happens after top coat. If your surface is not blasted clean, might as well use the POR.
 
(quoted from post at 08:41:00 07/30/19) Thanks for the experienced based information. I am thinking that POR 15 really doesn't add much value over epoxy primer. Your input seems to support that line of thinking. Any metal that is readily seen like the dashboard, rear of cab above seat, door frames and exterior I remove all of the rust and treat the pits with phosphoric acid. It is the floors, inside firewall and behind the seat areas that are going to be covered with carpet or sound deadening material that I want to shortcut the full rust removal. Thanks again.

Agreed here as well. Don't waste any time with the POR. I've used it, and don't see the point. It promises to work over an imperfect surface but at the same time is super finicky with any surface contamination. It is also full of isocyanates.
 
Posting to agree and stress the iso content of POR15. It has the same ingredient that 2k paints/clears have and everybody recommends fresh air supply apparatus(I don't but that's another discussion). Just suffice to say it is dangerous and I'm surprised more isn't made of that aspect.
 
for the places you cannot get totally clean, POR 15 is superior. I had a 54 Pontiac that I coated the rusty floor with Por 15 then laid in some fabric and recoated it. That was in 1983. I recently sold the Pontiac. The buyer lifted the carpet and the POR 15 was still shiny, solid and rust free. recently coated some parts that were cleaned well, treated with phosphoric acid and primed with epoxy primer. were then left out in a starage shed. 2 years later some mild rust was evident. I like to soak or fill seams such as in the bottom of doors with POR 15 and prime the exterior with epoxy primer
 

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