Why is POR-15 so frowned upon?

M

mitch_04

Learnin'
I've noticed a lot of posts that are very against POR-15 and I'm curious why. I figured it would be a decent paint for frames/suspension components. I tried to search but POR isn't long enough. I used it to coat the inside of a panel when I had it opened up for a patch. Is it for when people try to paint over it, or just a bad product in general?
 
por stands for paint over rust . you need to do way more research and gain much more experience before you attempt to enter the restoration business.
 
I understand it is paint over rust. I'm just trying to learn. If I had sandblasted a suspension component and painted it with POR15 for it's durability, would this be a bad thing. We all had to start somewhere.
 
Maybe it would help if I explained a little more about my history since there isn't an "introduce yourself" section here. I was born into a mechanic shop, 3rd generation. I started wrenching on bicycles, moved to motorcycles, and eventually to cars. I painted an old beater of my friends with tractor enamel when I was 14, my first car. I painted my own car when I was 16, first time using "real" paints and under the experience my fathers friend who was an auto body man. I have painted roughly 4 or 5 cars since then. I've been a mechanic by trade for about 7 years, went to tech school for it, and have another 4 years of experience before school. I am a great mechanic, I have no problem saying that. The reason I am a great mechanic is because if I don't know everything about something, it really bothers me. I never want to say I can't fix it, I will research and study until I can figure it out. I apply this sort of attitude towards everything. I'm a certified personal trainer as well, and an Army soldier with 9 years in. I have a hard time taking one persons advice without knowing why, I have been burnt before and on something like a full restoration it would be a big deal. However, I live 2 hours from any major city and I don't have access to paint suppliers or even many painters. Most painters around here fix a car when they hit a deer, but you can always tell what work was done. They don't take the pride in their work like I do. I understand some of my questions are probably simple, but the books I have read don't cover them. Going by books and reading online you would assume an acid etch primer or acid etching prior to primer is a necessity, but this forum has shown me otherwise. I don't plan on painting over POR 15, I just have seen many bad comments about it and was wondering why. I know I'm probably posting a large amount of questions, but I have a large thirst for knowledge. People around here will never spend 50,000 on a restoration, so I can't always do things perfectly. I will do them to the best of my abilities and will never do them lower than my standards. I hope this helps a little.
 
it depends what you use it for and how its used. por is a moisture cure urethane which there is nothing wrong with. the problem comes into play about how its marketed. a miracle rust cure that you can paint right over. it is not. it does have its place imo and i have used it here and there. my landscaper buddy for instance had a mower deck that needed done. i blasted it clean like i would for epoxy or any other paint then i used the por on it because it wears so well for what he needed. i have used it on trailers as well. its ok to use it but i dont believe you can paint over once cured and contrary to what they say dont paint over rust with it because it wont last long term. for suspension components, frames etc i personally only use black epoxy.
 
Epoxy is the best choice for bare metal because it has some flexibility to it. Just let a 1/4" layer dry in a paint cup and it will amaze you.
POR 15 tends to cure hard and brittle which can result in hairline cracks over time which will allow moisture to reach the metal.
Just that fact that it receives so many negative comments from professional painters ought to tell you something.
 
I am building a super-lightweight speedboat in my backyard. The hull is window screening that I'm spraying with Flex Seal. It doesn't do a very good job sealing my gutters but I'm sure it will be perfect for my boat.... Just busting your chops. My point is that POR-15 is mostly marketing hype. According to the flyer that comes with the "Super Starter Kit," I should use it to repair cracks in the fiberglass on my Corvette.

In a recent post on the Garage Journal, one of POR-15's advocates shows how it bonded the lid to the can so tightly that the lid had to be destroyed to get it open. If your goal is to bond a paint can lid to the can, it's the right product. Most of the guys who post on here are doing restoration work so they aren't looking for shortcuts. Their worst nightmare is to spend a huge amount of time on a restoration and then have the customer come back six months to a year (or even longer) with bubbles in the otherwise flawless paintjob.

Just think of the attributes of POR 15.
- It adheres best to rusty metal. For best results you have to find a way to get the shiny metal on your part to rust. Seems kind of backwards.
- Once cured, POR-15 is hard as a rock and about as flexible as plate glass. When applied to metal, the POR-15 expands and contracts at a different rate from the metal, so something has to give. The POR-15 still looks perfect but it has separated from the metal. You now have a rust manufacturing plant operating at maximum efficiency, completely out of sight under the POR-15.
- Ordinary paint doesn't stick well to POR-15. Once you've put it on, you need to apply a tie coat using one of POR's primers.

Best analogy I can think of is putting a waterproof, impermeable bandage over an infected cut. Looks good from the outside but who knows what's going on underneath.

Like most SPI users, I have made hockey pucks with leftover SPI epoxy. I have a couple that are years old and they still flex and bounce like they did at the end of their first week. Once you spray it on clean, prepped steel, it's on there for good and it flexes with the metal. Make a hockey puck with POR-15 and it's like a stone -- no flex at all.

Here's one of the discussions about miracle products like POR-15 that sums it up pretty well:
http://www.spiuserforum.com/showthread.php?497-zero-rust&highlight=por15
 
I had already planned on switching to epoxy after reading on this forum, but I also have some leftover POR 15 so I wondered if it was even worth using. We had used it on a '74 VW Bug floorpan. Thanks for letting me know what's up guys, main thing I took away is POR-15 is not flexible, so it has a better chance of cracking when flexed or impacted by rocks than epoxy! I had my can seal up tight on me as well. I poured out my excess on a small cement slab outside our door, interested to see what happens!
 
after seeing up close the cracks in POR 15 on undercarriages( i hadn't used it yet) i started researching. i didn't want to put something on that would be cracking and causing more problems down the road( and northern Michigan roads are a lil hard on undercarriages).
i learned some flexability on an undercarriage( and other areas of a vehicle) is a good thing. i have used a product called zerorust and it has held up pretty good on an 87 blazer daily driver for 2 years.
HOPWEVER...hearing nothing but good about SPI's epoxy, the next time i get a job like that, im gonna use it.
 
So in other words, there really isn't a single place it should ever be use on a car! Maybe I'll put a second coat on the cement slab with the left overs...
 
mitch_04;30352 said:
. . . I poured out my excess on a small cement slab outside our door, interested to see what happens!
Click to expand...

It will stick to concrete like crazy! I painted the inside of the holding bin on our combine 2 years ago, and managed to spill a little on the concrete slab below, and it's still on there. BTW, the POR has held up pretty well under the flowing grain, but there is one spot where it has peeled up.
 
I agree with Jim C. POR is nothing more than a moisture cured ureathane and, as such is perfectly fine if used as such. Beyond being brittle and, prone to failure without proper surface prep and epoxy primer, it fades very quickly in UV. Why pay the inflated price (almost $50/qt. as I recall) for some thing that wont even work as advertised. As Barry said, if it was a good product for the advertised use, all the majors would be making it. The auto paint suppliers here don't carry it.
 
Thanks everyone. Before I started the thread, I had gathered it was generally not something you want to use, but was curious as to the reasoning. Thanks for all of the explanations, that's exactly what I was looking for. It does stick to concrete, and holds gravel together very well also (had a little run off)! I know it has a low resistance to UV, which is why their concrete coating has a slightly different mix, or you can clear it with UV protection if I remember right. However, their garage coating is ridiculously priced as well.

Anyways, thanks again for all of the solid info.
 
We used to use moisture cured ureathanes on concrete, slate and, porous tiles to seal and bring up a high gloss. It was very durable as a sealer. And fast drying. If you wanted a faster dry after application, we would mist water on it with a spray bottle. POR 15 will do the same.

Are there applications appropriate for MCUs? certainly... but, not on my cars
 
Why is POR-15 so frowned upon?
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Number 1: because this is SPI epoxy forum. :)

I have had the same poor results with poo15. I had a brochure from a car show that makes this stuff look like the ultimate do-all end-all frame paint. So, when I restored my frame, that is what I bought.

If the sun, moon, earth and winds are in perfect alignment, you will get decent results. In my case, the first coat was too tacky to respray the second coat during the stated recoat window, so I let it sit a few hours longer. The second coat balled up into lumps because the first coat was over-cured. If you aren't in the perfect exact small respray window, you have to use their etching primer to get anything to stick to it! I sanded off the lumps, bought the $$$ etching primer and proceeded. I should have taken it to a sandblaster and started over with REAL paint!

Last week, I took some of the poo15 to pour in a lightly rusted seam. It seamed to convert the rust to black. Where it spilled out, I sanded off to bare metal again, because epoxy won't stick to it. The hockey puck left in the cup is as hard as a rock and will not flex. The epoxy puck I have is very flexible.

The only place I would use this stuff is in an area that will never be painted over or be seen again. Like the title says, "P"aint "O"ver "R"ust, not clean prepped metal. You have to use their cleaners, etch and prep first, or it will not stick. I'm doubting the long term durability of where I poured it into a seam, because I did not do the clean, etch, rinse, etc in the seam. But, it is better than nothing at all.

In the end, it is cheaper and EASIER to use epoxy / SS top coat, than buy all of the por products (metal wash, metal etch, self etch primer, -15, and chassis top coat).
 
I had a car I was working on one time. it was a mid 80's jag, it had to go outside with the fenders off.. the aprons had surface rust on them. I decided to try the por15 on them. long story short, the car ended up sitting out there for a few years, and when we decided to send it to the scrap yard I checked out the aprons.. and they were in worse shape than the stuff that hadn't been covered in the POR15..
 
undercoating ................. rust hotels since the 50's . a wise old indian one told me " what there when start , be there when done "
 
shine;30398 said:
undercoating ................. rust hotels since the 50's . a wise old indian one told me " what there when start , be there when done "
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Lmao.. well put.
 
Another thing I've been curious about is "sealing" metal. Rust is oxidation, which needs oxygen to happen. Let's say you have a rusty piece of sheet metal, just a square chunk for ease of conversation, and coat each side completely. I don't care if you use POR-15, epoxy primer, whatever, but each side is coated. Now, this is where I may be off, since the rust is sealed from oxygen, how is it able to continue rusting?

Is it because none of the coatings can seal over rust? I understand polyester primers, body filler, etc etc all "breathe" which would allow the oxygen to reach the metal so it could further oxidize, but don't coatings like epoxy, POR-15, etc etc all seal the metal from oxygen? Please, please don't read this as me justifying painting over any kind of rust. I haven't and don't plan on doing this. My use of POR-15 was always under the assumption that it was very chip proof and sealed well, on pieces that didn't see sunlight and were previously sandblased or clean bare steel. I'm purely curious as to how rust can continue to form when it is sealed off from oxygen.
 
I do not know the answer to that question but I think it has something to do with sweating underneath the por-15, which causes more rust. but I am not sure on this at all to be honest.

BUT. if that is the case why wouldn't you just apply epoxy over a surface rusted panel instead of the POR.. Epoxy will seal out the moisture and is very chip resistant.
I would never suggest that, nor do I understand the idea of leaving rust in a project, but just because they advertise it over rust people seem to swarm to this stuff. I think they marketed it this way because of the fact that it's a easy target, they directly marketed the product to the do it you're self weekend hobbyist.. The first time I saw the stuff was at a car show, the guy had a booth and was beating on different pieces with a hammer all day and crumpling it on tin foil.. His marketing made it hard to resist. I admit I had to get some and try it myself, but after using it I surely wasn't impressed with the results.
 
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