The Complete Guide to Painting Stainless Steel
Application Data Sheet Stainless Steel
Painting Stainless Steel
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Stainless steels have an aesthetically pleasing appearance, and can be further polished or painted to enhance this feature. Painting may actually reduce the corrosion resistance, but may be required for other reasons such as product marking or identification, or for the protection of carbon steel welded to it.
Surface preparation prior to paint a stainless steel surface is as important as it is for carbon steel. The preparation required will depend on the surface finish of the stainless steel.
How To Prepare Stainless Steel for Painting
Cleaning is usually carried out after welding or fabrication, including removing heat tint from welds. The cleaning required depends on the intended application as well as the coating system to be used. The recommendations of the paint manufacturer should be followed. Also do not use steel wool during preparation as this is typical made of carbon steel which can leave residues causing rusting on the surface of the stainless steel surface.
Mill scale on HRA and welding or heat treatment heat tints can be removed by pickling with pickling paste, or by immersion in a mixture of nitric and hydrofluoric acids. Consult Austral Wright Metals for details. Thorough rinsing after pickling is essential.
This method of cleaning is particularly useful for large structures and is highly effective in removing mill scale. Blasting media must be clean, free from metallic iron, not previously used on carbon steel and free from chlorides. Suitable blasting media are washed silica sand, stainless steel shot, glass beads. It is advisable to passivate the stainless surface with nitric acid after blasting to remove any possible carbon steel contamination and ensure optimum corrosion resistance.
Other methods of preparing stainless steel for painting
Small areas can be cleaned with a stainless steel wire brush, disc grinder, flap wheel or other abrasive. Use only clean, uncontaminated consumables intended for use on stainless steel.
All fabrications should be degreased to remove the shop soil almost inevitably picked up while being worked.
Water soluble solvent degreasers are most easily used. Consult the paint supplier for details.
Cleanliness can be checked by ensuring that the surface dries water break free.
How To Paint Stainless Steel
The appropriate paint system depends on the application, the surface condition of the steel, and the degree of protection required.
This guide covers generic paint systems. Manufacturers have their own proprietary versions of the systems, and will provide advice.
Cold rolled stainless steel with a 2B or BA finish has a smooth surface profile, and requires a primer coat to ensure good adhesion.
Types of Paints for Stainless Steel
As with many other substrates for painting, there are different types of paint available. Lets look at those commonly used for stainless steel paint. Remember as already mentioned it is important to consider applying a primer before applying any type of paint to the bare steel.
Oil Based Paint
This type of final coat paint is not always readily identified as suitable for stainless steel, however it is commonly noted for metal finishes. These paints can smell bad as they usually contain solvents, which can also be flammable. They also take longer to dry than other pain systems.
Once fully dried and cured, these paints are very tough and do not easily chip or stain, and . Oil based paints are available in many colours and finishes, eg matte, flat and gloss.
Water-Based and Acrylic Paint
Water-based or latex and acrylic paints dry much faster than the oil based paints. In general these paints are far easier to work and easier to clean up. They also come with endless colour range and finishes.
The down side to water-based paints is they are not as tough and hard-wearing as oil-based paints.
Epoxy paint is the preferred coating system for stainless steel. It requires additional preparation and care over that of water based and oil based paints, however they are extremely tough and durable, and if applies correctly have excellent paint adhesion.
This system is a two part epoxy paint formula that requires the mixing of the resin paint with a hardener, which acts as a catalyst that sets in motion the polymerization or hardening process. Care must be taken when both measuring the required part of resin paint and hardener, and ensuring thorough mixing of the two parts.
Applying Primer for Painting Stainless Steel
Firstly not all primers work on stainless steel. Ensure you read the product data sheet to confirm compatibility with stainless steel. Also primers require an intermediate coat and/or topcoat to be applied to complete the system.
In general before applying a primer the surface should be roughen by grinding or sweep blasting using non-metallic abrasives. Then any oil, grease, salts and dirt should be removed. However some primers claim to make a perfect chemical bond without the need for blasting or etching the surface beforehand, however the surface should still be degreased using an alkaline or high pressure (steam) cleaning process.
Key Facts about Painting Stainless Steel
Chlorinated rubbers & vinyl top coats should not be used for operating temperatures above 70°C.
Alkyd enamels should not be used in alkaline or aggressive corrosive environments.
Paint manufacturers should be contacted for advice on the suitability of paint systems for particular environments.
Welded stainless steel
When stainless steel is welded to carbon steel, and the carbon steel is to be painted for corrosion protection, the paint should be continued over the weld and about 25 mm of stainless steel adjacent to the weld. This is particularly required for immersion service or wet areas, where the stainless steel could accelerate the corrosion of the carbon steel.
Frequently Asked Questions
Can You Paint Stainless Steel?
Yes. Like all painting jobs the key is preparation and choosing the best paint system. Epoxy, or two part paint systems, provide the best protection.
Does Stainless Steel Rust?
Yes, but the term rust is more commonly associated with the corrosion of carbon steels. Stainless steels can also corrode, some more than others. The higher the chromium content the less likely the stainless steel is to corrode.
Will Spray Paint Stick to Stainless Steel?
Yes, with the correct surface preparation and a suitable primer, spray paint will adhere to stainless steel.
Can you paint over damaged stainless steel?
Yes, with thorough clean or etching, and a suitable primer, you can paint over damaged stainless steel. See cleaning stainless steel for more information.
Consult the local yellow pages for paint suppliers.
A comprehensive list of paint manufacturers is provided at http://www.apmf.asn.au
The following information is provided without endorsement by Austral Wright Metals:
Wattyll Pty Ltd phone 132 111 http://www.wattyl.com.au