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Painting the underside after blasting


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I'm just about finished tearing down my MJ for a full restore and I'll send it off to have the underside blasted. I need some advice on what to paint it with afterwards. My idea is to use paint for steel hull boats, it seems really logical to me that this would give great protection since these boats are exposed to saltwater constantly for decades before needing to be repainted. Thing is, while this seems obvious to me I have never seen anyone else use these products, why is that. anyone out there have any good arguments why it would/would'nt work?

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What about the rubberized "undercoating" I see on the shelf. Is that stuff any good? I find the stuff coming off in places. Is it just for sound deadening or ??

 

I agree with the POR-15 though and I like the idea of a smooth surface. The undercoating seems like it would be harder to clean and the times when I've seen it peeling off is when I'm blasting the underside with a hose. I truly don't have many rust issues here. However, the PO of my MJ did a horrible job of maintaining certain parts of the truck.

 

So, will you, or have you pulled the bed off??

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I have many friends in the navy, I am army myself, after talking to them. They say one of the most labourous and painstaking tasks is constantly repainting the boats. Everytime they pull into harbour they repaint the boat with this stuff you were talking about. And as a personal opinion, anything you put on the underbelly of your baby could get scraped off anyways.

 

Find the even balance between price and suitability.

 

My two cents.

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What about the rubberized "undercoating" I see on the shelf. Is that stuff any good? I find the stuff coming off in places. Is it just for sound deadening or ??

Rubberized undercoating is for separating customers from money. It doesn't adhere tightly to the metal, but it is cohesive enough that when moisture gets behind it the moisture stays trapped so it can continue to attack the metal for a long time. POR-15 bonds well to bare metal and provides excellent protection against rust. However, POR-15 is not UV resistant, and that's why it should be topcoated with a couple of good coats of some decent enamel that will effectively protect the POR-15 from daylight.

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So far....you're all right.

 

I would do as eagle says and por 15 it, then paint it

 

But....I would also spray undercoating over the top of that paint, at least in certain areas. It will cut down on road noise as well as give you a little abrasion resistance in easily worn or scraped areas

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I'm just about finished tearing down my MJ for a full restore and I'll send it off to have the underside blasted. I need some advice on what to paint it with afterwards. My idea is to use paint for steel hull boats, it seems really logical to me that this would give great protection since these boats are exposed to saltwater constantly for decades before needing to be repainted. Thing is, while this seems obvious to me I have never seen anyone else use these products, why is that. anyone out there have any good arguments why it would/would'nt work?

 

POR-15's definitely the way to go. It is a marine-grade product, and I've known guys who use it as a base coat on metal boat hulls. Most marine base coats are epoxy based - and IMO they're a pain to mix and apply, expensive, and heavy. POR-15 is basically the same thing - a hard seal protecting the metal from moisture - so it replaces the epoxy base coat.

 

I'm definitely not an expert, but here's my ham-fisted understanding of it: With boats, it's not so much the paint that stops the rust/corrosion. Saltwater is an electrolyte, so a metal boat hull sitting in the water is like being in a battery. And the majority of corrosion control comes from the sacrificial zincs and isolated grounds for the electrical system to guard against stray currents and the galvanic corrosion that happens underwater. So marine paints are formulated with specific metal content and pH levels. They also contain pesticides to inhibit the growth of barnacles, algae, etc. Most marine paint is designed to be sacrificial - leach off to keep the hull clean, and it loses it's effectiveness over time. That's why boats have to be hauled out and re-painted every year or so.

 

Those properties are overkill and wasted on a car. If you go the POR-15 route, and then cover it with a few top coats of rustoleum for UV protection, and then maybe some rubber undercoating for sound deadening, you'll be getting the same level of protection.

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Thanks for the advice guys, think i'll go the POR-15 route.

 

mfpdm: how much POR-15 did you use to cover the underside? did you spray or brush it on? this stuff is really really expensive here, the only supplier i found charges about 100 USD for 1 liter (a little less than a quarter gallon) :eek: So I don't want to buy much more than I need.

The POR-15 chassiscoat is not available here so I think I'll use the tiecoat instead and then the undercoating.

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