View Full Version : Por-15

Kev Williams
07-27-2015, 11:42 AM
I'm looking for pros/cons with this stuff...

We have a steel-hulled houseboat (50' SkipperLiner), we've owned it for 9 years, and was in the water the past 4 years. It started taking on water on Father's day. Short version is, this boat has a DC power leak to the water, and the hull has has been getting eaten away by stray current corrosion. Couple of pics attached. NOTE that while the hull looks like it's been eaten away by rust cancer, the only rust whatsoever is the surface 'flash' rust on the steel that's been bared by the the electric corrosion. There isn't a bit of rust-caused corrosion. Of course, as I do the repairs, keeping rust corrosion from starting is priority 1 :)

Once an area is repaired I'll be down to bare metal that will need to be treated almost immediately...

Once all the repairs are done-- about 25% of the entire hull- then comes prep of the remaining hull for new coatings.

The tried & true coating for steel boats is coal tar epoxy. It's cheap and it works.

So- is POR-15 all it's cracked up to be? My thinking is to use their etching prep and basic coating over my repairs, and then 2 coats of coal tar epoxy over the entire hull...

Next question, I notice POR-15 also comes in a DIY brush-on bedliner. I've heard good things about coating boat hulls with other liners like Rhino lining, etc. Just wondering if anyone has an experience with the POR-15 bedliner? At $100 a gallon I can 2-coat the hull for $1200 or less, which is a bargain if it's do-able. I would think it should adhere very nicely to freshly applied and dry coal tar epoxy- but I don't know. A couple of benefits of adding POR-15 bedliner to the coal tar epoxy will be the thickness of the coating, should be more than 1/32" thick. This will act as electrical insulation in the future. (I'm still looking into the source of the DC leak). There's also the rust-preventative qualities...

Stray current corrosion mostly affects sharp edges, that's the easiest place for current to escape into the water to search for a ground. As the current leaves the boat, it takes metal with it. First pic shows the starboard (worst) side, the closeup is the area under the blue fender. The bottom has several places that need repairs also, but in most cases the corrosion damage is pretty minimal. I've treated the exposed rust with tannic acid to keep it in check for now, that's why it's dark...


Anyone with any real world experience with POR-15 products? Any other product suggestions would be welcome also!

Ole Anderson
07-27-2015, 2:07 PM
I would sand blast to white steel and coat directly with a marine grade epoxy primer, coal tar or otherwise. Fresh or salt water determines the top coat. As far as POR-15 base coating, I know it is supposed to be great on vehicle chassis. And it is tenacious if you get it on something you don't want it on. And it must be top coated. As far as stray currents, I presume you have a sufficient number of sacrificial zinc anodes? And there are active (powered) systems to prevent or counteract the problem you have. My experience is specifying products for painting steel elevated water storage towers.

Larry Frank
07-27-2015, 7:31 PM
If you are already using a passive protection with zinc and it is not sufficient, I would look at an active protection system maybe something like offered ElectroGuard by would work.

Coatings are good but even a small hole in a coating can result in accelerated pinhole corrosion.

James Tibbetts
07-28-2015, 10:55 AM
I spent a fair amount of money and a LOT of time prepping and applying POR-15 products as per manufacturers instructions to the frame and other metal parts of my pick up. I have never had a product(s) with which I was more displeased!! In less than a year there was separation of the finish, caused by rusting of the treated surfaces. IMHO avoid like the plague.

Kev Williams
07-29-2015, 7:26 PM
Thanks for the replies everyone! I think I'll skip the POR-15, and stay with tried & true: plain old phosphoric acid prep on the bare metal, followed by coal tar epoxy.

Ole Anderson
07-29-2015, 10:22 PM
Thanks for the replies everyone! I think I'll skip the POR-15, and stay with tried & true: plain old phosphoric acid prep on the bare metal, followed by coal tar epoxy.

Manufacturer recommends blasting to clean metal:
"BARE METAL: Surface should be blasted to bright metal. Remove all blast or sanding residue using a clean air line and sweeping with a clean brush or broom. Vacuum clean for best results. Apply (coal tar epoxy) primer within 1 hour of metal preparation. If blasting is not possible (or if more than 2 hours has passed since blasting) sand or grind with coarse 36-60 grit discs. Remove sanding dust."

And as far as I know, the epoxy is just a primer and is intended to be top coated.


Kev Williams
07-30-2015, 5:25 PM
Affirmative on coal tar epoxy just being a primer. I'm still debating the pros & cons of a bedliner-type topcoat. I have found a few hard used boats with Rhino-lined hulls and the owners couldn't be happier. I don't really need Rhinolining, but it WOULD provide more sealing of the hull, and the added thickness means more space between the water and the steel to act as an electric insulator.

Regardless of what goes on first, what will go on last is good old cheap Pettit Unepoxy antifouling bottom paint...

Scott Shepherd
07-30-2015, 5:47 PM
Kev, you just need this stuff....



John Lohmann
07-30-2015, 10:43 PM
rust bullet?