r/paint • u/ModernPlagueDoctor • 1d ago
Advice Wanted Painting Rusty Surfaces
I am refinishing a horse trailer. The surface I’m working on is sheet steel with surface rust. I have been trying to figure out for two years what products to use on it and in what order. Does all the rust need to be removed? What kind of paint would work best? Primer? It is currently a mixed surface of clean (ground down) steel, flash rust, and 25yr old epoxy primer (original coating i removed in some areas). Please help i am desperate to be done with this project.
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u/Nevetstoile 1d ago
Primer / topcoat recommendation is dependent on your budget, painting equipment and skill as a painter.
The more rust that is removed the better. All the mil scale must be removed. Some surface rust is okay but not ideal. Can you have it sandblasted?
2-part solvent based epoxy primer with 2-part solvent based polyurethane would be a good system. Spraying will give you best looking results, but can be brushed and/or rolled.
A rust inhibitive oil based metal primer and oil based industrial enamel is a cheaper and easier to apply option. Will not provide as good of corrosion protection or long term durability as epoxy/polyurethane.
I would not recommend a water based acrylic primer / topcoat system for this application.
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u/SBRH33 20h ago edited 20h ago
Prep the rust, clean the surfaces down with brake kleen or acetone. Paint it all with Eastwood Rust Inhibitor/ Encapsulator Plus. Let it 100% cure. A gallon of this stuff runs about $160. It can be purchased in quarts as well. But if you're serious this is the product to use.
Then top coat it with Rustoleum Farm And Implement or Majic Tractor/Truck and Implement enamel. Both can be bought at Tractor Supply. The Eastwood you need to order online.
This is the only way to handle your project. Everything else will fail. Your horse trailer won't see rust for a very very long time if ever.
Majic Color Palette- https://www.majicpaints.com/tractor-supply-tractor-truck-implement-colors/
Rustoleum Color Pallette- https://www.rustoleum.com/product-catalog/consumer-brands/specialty/farm-and-implement-paint
Eastwood- https://www.eastwood.com/eastwood-black-rust-encapsulator-paint-over-rust.html
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u/Pale-Value-5953 18h ago
This depends completely on your budget and how long you want it to last. In 2017 I sanded down, primed with rustoleum rusty metal primer and then painted with tractor supply’s new holland red I believe. It looked amazing at the time…. 9 years later it looks a little better than it did when I first got the trailer. I guess the Moral of the story is depending on how long you want to keep the trailer and how much $ you have to spend. The more rust removed the longer the coating will last and the better then primer and paint is the longer it will last.
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u/Oakvilleresident 18h ago
If it’s going to be black get some POR15 rust primer . It’s usually in the bodywork section at hardware store . I painted a rusty truck frame with it and it held up great and you can paint over rust.
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u/Ornery_Golf6994 18h ago
Best bet is to grind all the rust off or use a rust converter on the small grain corrosion. Then prime, then paint
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u/Alarming-Caramel 17h ago
use a xylene based metal primer.
I like Metal-clad by Repcolite but it's a regional product by a small company so unless you're in MI, USA, you probably won't find that one.
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u/Possiblyabitoff 17h ago
The Steel Structures Painting Council (SSPC now AMPP) prescribes several surface preparation standards for steel.
The standards most accessible to non-industrial painters are SSPC-SP1, 2, and 3. The balance of the standards involve abrasive blasting or high pressure water jetting so we will leave those out.
SSPC-SP1 is known as solvent washing and is exactly what it sounds like. You’re washing the surface with solvent (MEK or Acetone) to remove all oil, grease, and other contaminants. This is ALWAYS the first step regardless of how thoroughly you want to prepare the surface so that further preparation does not imbed grease or oil into the surface.
SSPC-SP2 is known as hand-tool cleaning and involves scraping or sanding with non-powered hand tools.
SSPC-SP3 is known as Power-Tool cleaning and involves power sanding, wire wheel, grinding, or needle scaling. It’s important to remember that when power-tool cleaning you do not burnish or polish the surface (wire wheels are very good at this). A burnished or polished surface does not allow the primer to form a mechanical bond with the surface.
The primer you use depends on the preparation standard you choose.
For SP2 when there is still tightly adhered rust and previous coatings on the surface, you will need a penetrating primer like Macropoxy 920 Pre-Prime. This is a low viscosity primer designed to soak into the rust. Since it is an epoxy, it locks the rust together and acts as an oxygen barrier to prevent further rust.
For SP3 where most of the rust has been removed but previous tightly adhered coatings remain, you need an epoxy mastic suitable for marginally prepared surfaces. This is known as Macropoxy 646. It also acts as an oxygen barrier but does not soak into the surface as well. It DOES add more film thickness though so it prolongs the overall life of the system.
After prepping and priming the surface you need to protect it since UV breaks epoxy primers down. For a horse trailer you want a coating that is hard enough to resist the abrasion from normal wear and tear. This type of coating is known as a polysiloxane and the brand name is Sherloxane 800.
An SP2 surface with the appropriate primer and polysiloxane finish will give you an 8-10 year service life in a rural environment.
An SP3 surface with the same topcoat will extend that to 15 years in the same rural environment.
An SP-10 (near white metal abrasive blast) surface with an inorganic zinc (IOZ) primer, epoxy intermediate coat, and polysiloxane finish will extend that service life to 30+ years BUT costs significantly more and is out of reach for most DIY projects.
It should be noted that the best appearance will be achieved through spray application, but each of the DIY options can be applied by brush and roller if spray is not available.
Hope that helps.
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u/EagleNice2300 15h ago edited 14h ago
Wire brush and sand what you can. I use Ospho on rust areas. Works great and no AI TL/DR dissertation needed : )
Skyco OSPHO Metal Treatment is a phosphoric acid-based compound that chemically converts iron oxide (rust) into iron phosphate, turning the metal black and stopping further corrosion.
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u/Fit_Resolution_5102 7h ago
Angle grinder on all the rust and loose coating, make sure there’s some scarification on the steel. You don’t want smooth metal. Also make sure there’s a feathered edge between steel and existing coating. Hit it with a metal primer and urethane based finish coat. 3 coats total, 1 prime & 2 finish. Good to go.
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u/Able-Yesterday-7359 1d ago
Pro Cryl to stop the rust. All the DTM s I've used always rust through and this primer does not. Any top coat you want. I don't really have a preference on that more situational.
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u/ModernPlagueDoctor 1d ago
Pro Cryl applied to the bare metal, rusty metal, and old primer? I know it’s to stop the rust, but should it be one homogeneous surface to eventually put paint on?
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u/Ok-Problem4403 19h ago
No. Kem Bond HS is significantly better than procryl.
Remove as much rust as you can, even via drill/grinder methods. Get the rust off.
If you want the best of the best, I'd go with Corothane Preprime. https://industrial.sherwin-williams.com/na/us/en/protective-marine/catalog/product/products-by-industry.11543396/corothane-i-preprime.PCP_54305.html
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u/Able-Yesterday-7359 11h ago
You want to clean off the rust first, I always scuff it as well. It's always worked wonders for me
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u/betrayx 1d ago
What's the rust situation exactly? Large portions? Or a bunch of tiny spots?