All About Painting: Dealing With Rust

By Vancouver’s Best Painters www.vancouversbestpainters.com
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Dealing With Rust - Page 1/2

Whether you find it on your tools or on the job, rust cannot be allowed to linger

It takes nothing more than for iron’s exposure to oxygen to create iron oxide, or rust. And it only takes a little rust to leak through your paint job on a railing or a holding tank to make your work look very, very, bad. The three keys to dealing with rust are the same three things you use to deal with all paint applications—prep, prep, and more prep. Here’s what we mean:

Prep 1: Customer prep

As mentioned, rust happens when iron meets oxygen, but it happens a lot faster if some other environmental conditions are present as well. Dampness will accelerate rusting. Electrochemical reactions between dissimiliar metals close together will cause rust to occur. Salt hastens rust. Heat also makes rust happen must faster. So, before before you do any surface prep, take a look at the surrounding environment and assess whether there are recommendations you can make to your customer to reduce the chances of rust coming back. Will a dehumidifier reduce the dampness? Is the heating system or the air conditioning allowing temperatures to rise too high? Is the surface you are painting made with two metals that will react to each other thereby causing rust?
There may be circumstances that will cause rust to reappear that your work will do nothing to alleviate. Imagine, for instance, that you have a rust stain appearing on a wall. Examination revelas that the stain is being produced by moisture getting to the back of an iron fixture attached to the wall. You can remove the rust stain, and repaint the wall, but the rust will reappear because the underlying problem was not dealt with. (the iron fixture was not properly under4coated where it is attached to the wall)
Good investigation and informed communication with your client before you start ensures that he understands the conditions you’re working with and the limits you have in dealing with his problems. Your customer needs to understand that preventing future rust is sometimes not entirely up to you.

Prep 2: Rust Removal

You can remove the rust with sanding, scraping, wire brush or wire wheel, and/or blasting. These mechanical methods are environmentally healthy compared to chemical methods, but you end up removing good steel along with the bad and – in the case of sanding and scraping – you may not get all the rust. That may not be good for the application in question.
Sanding should be done in stages. Start with 80 grit and go up to 120 or a little higher if you need a smooth finish. Sand blasting or bead blasting is better and easier and will get into the corners, but it removes a lot of good steel.
Chemical rust removal tends to get better results—phosphoric acid or a solution of phosphoric acid, alcohol will remove rust and wax and oils that can accumulate on metals. It is often used in body shops as a prep before priming to remove latent rust after sand blasting.

When you use phosphoric acid alone, it will leave a fine coating of iron phosphate behind, which actually prevents rust as well. Unfortunately, the protective layer is easily scratched and will not hold up to wear. You still need an additional application for long term rust prevention. Hydrochloric acid will also remove rust, as will oxalic acid, and they act quickly, but they also remove some metal along with the rust and they don’t leave behind a protective coating as phosphoric acid does.

Of course, there is a very big downside to these acids. They are extremely toxic. You cannot neglect any of the recommended safety procedures or disposal instructions, which means the set-up time will be longer. Be sure to wear adequate protection (gloves, the correct mask, eye protection) and read the WHMIS label that comes with the product for proper handling.
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