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tesstoaster 07-28-2012 08:54 AM

POR15 or Zero Rust
I have used both products but only have experience with POR15 on a longer time frame. The POR15 is normally brushed on due to it's toxicity from the isocyanates. The Zero Rust can be sprayed or brushed. According to the Zero-Rust website:


Zero Rust makes an excellent Original Equipment Manufacturer “OEM” coating and is routinely used on new trailers, new structural steel, new oilfield wellheads & manifolds, new mining equipment, new pump & manifold systems, new power generation skids and new tanks.
Although I think that POR15 is a great product, I did find that it behaved much like a powder coat in a corrosive environment where is came off in large sheets. This was my experience with the underside of my lawn tractor deck.

The Zero-Rust is considered a Direct To Metal (DTM) coating and adheres well to treated rust. Any first hand accounts with this coating on a rusty AS frame?

purman 07-28-2012 09:09 AM

The key with por15 is prep. I sprayed mine on with no problem and it has worked great. I have had no flaking what so ever. But I used a wire brush in a grinder on the frame and then cleaned it with a pressure washer.

I also clean my tractor bucket and pressure washed it. I then sprayed some extra I had on the inside and outside of the bucket. I haven't had a ton of use with the bucket yet, but did move about 12 loads of gravel with the bucket and had very little paint come off. Just a few scratches in the paint.

tesstoaster 07-28-2012 09:29 AM

I think the other potential issue I have with POR15 is that it's affinity for previously painted surfaces might be relatively low. My trailer frame has much of the original paint, it is only the rear that was hard hit by the rust.

In the case of my tractor deck, it was thoroughly wire brushed and then the rust was converted with Ospho until all rust was black. When the POR15 started coming off in sheets a few years later, the iron oxide was again present underneath the POR15. I will agree however that the underside of a mower deck is about as bad as you can get as far as a hostile environment for a coating.

I have learned that a powder coat like coating is the very worst coating you can have on steel in a marine and corrosive environment.

Wabbiteer 07-28-2012 09:59 AM

I would have liked to see the mower deck had the Ospho step been omitted.

Purman is correct, its all in the preparation. If you have just a small area of the frame you can afford to strip the OEM undercoating/paint off and prep the metal according to the POR company best practices recommendations.

Here are some POR application after and more-after photos - I *thought* I'd prepped the frame *good enough* the first go-around - however the angle grinder twisted brush and flap sanders bounced off properly applied POR while the rest vanished...

Frame with quick POR-treatment (2nd photo, sure didn't seem like it at the time)

The same frame after truly going ballistic on it...
(The areas black is good POR :) )

barts 07-28-2012 12:16 PM

This is what I use:

MCU Aluthane (tm) - Moisture Cured Urethane Metallic Aluminum Paint

It's a moisture cured, aluminum filled polyurethane.

Very tough and strong - we painted the epoxied floor in our Airstream with this, as well as sections of frame.

From the link:


A moisture cured urethane, aluminum flake filled, that non-epoxy was specifically formulated as a primer over less-than perfectly prepared surfaces. Use in temperatures down to 40 degrees F. However, this coating often ends up as an aluminum colored topcoat. We're impressed with the ‘fresh galvanized' look it gives back to boat trailers. Also makes aluminum masts and booms look new. Gives engines and other mechanical equipment that dealer fresh look (or primed and ready to repaint status). On smooth surfaces it has a 'flat' galvanized look. On rough surfaces it has a shiny silvery look. Unique penetrating urethane chemistry seals and covers rust, keeps it from ‘rusting back through.' We know this is a great product - we can't get it off your hands even after days of normal washing and wear. The real aluminum flakes can handle temperatures of several hundred degrees (and resists burning better than regular paint). Used industrially on large metal tanks, bridges, and piping with or without topcoating. A truly unique primer AND/OR attractive metallic topcoat. Because of their amazing bonding, commercial painting contractors use moisture cured urethanes on surfaces that they cannot prep as well as they would like to. You should too! One quart units cover up to 100 square feet (about 75 square feet on rough surfaces and 100 sf on smooth).
<no relationship other than a satisfied customer>

- Bart

perryg114 07-28-2012 04:29 PM

Next time sand blast the mower deck turn it over and let it rust for month then put the POR15 on it.


tesstoaster 07-28-2012 06:23 PM


Originally Posted by barts (Post 1179988)
This is what I use:

MCU Aluthane (tm) - Moisture Cured Urethane Metallic Aluminum Paint

It's a moisture cured, aluminum filled polyurethane.

Very tough and strong - we painted the epoxied floor in our Airstream with this, as well as sections of frame.

From the link:

<no relationship other than a satisfied customer>

- Bart

Any chance the aluminum in the urethane can create an electrolysis reaction against the steel or is every particle insulated with the urethane?

BTW, just finished stripping the clearcoat from a 25' Tradewind with RemovAll 220 . It took me about five hours and one gallon of the RemovAll. Absolutely wonderful product. I would say 99% of the clear coat came off with the first application. I nice cool overcast day was in my favor. A light misting one hour after the application seemed to really help.

Wabbiteer 07-28-2012 07:10 PM

I checked the POR site and they spell this out about their own "aluminum filled" paint...

"POR-15® SILVER contains metal (aluminum) filler and should be used on badly rusted steel to fill small holes and pitted areas."

After those microscopic flakes of aluminum have been mixed into the paint serum there is zero chance of reactions with iron or anything else...

dkrukosky 07-31-2012 09:52 AM

Sorry I have not read the directions but my thought was that pro 15 was made to bond to the rust so, wouldn't over cleaning/sand blasting be a bad thing? I have 2 quarts of the stuff on the way for my frame. I plan on spraying it on. Also I will be boxing in parts of my frame dose anyone know of a device that will spray inside a tube?

Wabbiteer 07-31-2012 10:56 AM

Eeegads, I think I need to finish my Overlander and go fishing - I seem to be a spokesman for the 7th circle of frame restoration society.


made to bond to the rust so, wouldn't over cleaning/sand blasting be a bad thing?
Good question... It all comes down to percentages beyond 3-5 years - most anything will give 95 or 98% protection for the first couple of years and on a modern consumer time scale that'd be adequate. (cue RV informercial) That's the freakish thing about moisture cured polyurethane - Aluthane, POR-15 etc. is with the same investment of preparation time its 20 or 30 years of 99+% protection.

The way the paint keys into texture means a thin film of rust is used against itself. The zinc etching treatments provide even better texture. Think Velcro hooks into loops versus hooks into denim or leather.

The first coat soaks in to every crevice, pore and cranny and the second coat glaze seals out the elements from any remaining flaws. Paint POR-15 over the OEM frame undercoating and it will peel away like shrink wrap. Paint it over polished metal and it will likely peel away anytime the film is tougher than the paints bond. So chemical etching is a big payoff.

Rougher rust scale might hide voids and pits that the paint won't wick into, or leaving texture that will break off later and allow a rust pit to thrive. That's about all I found after a couple of years, places I had bubbles in the paint covering a pit which continued to deepen but not spread - weld crevices, rust pits, etc.. Its really talking about the last 1/2 of 1% protection - that may be welds or already weakened metal.

If the surface texture and appearance is not important due to preserving as much thickness of the existing (antique, irreplaceable, historically significant) and the item will never suffer years of weathering (garage kept hot rods etc.) then POR-15 can be painted over ANYTHING, just get the mouse nests, bugs & mud dauber nests and snake skins off first :bb: :cool: :angel:

tesstoaster 07-31-2012 11:49 AM

Lot's of debate on other sites about moisture cure urethanes, isocynates and modified alkyds. A lot of professional restorers are using Zero Rust with success, while others are saying it is nothing but glorified Rustoleum. I think it really depends on where the POR15 is being applied. If just subject to humid air it is probably the way to go. If constantly exposed to water, especially on the coast, I think once the rust starts underneath the coating, it will fail just like powder coating and then you have a mess.

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