In order to properly prepare metal parts for painting, one must follow a few key steps in order to promote the best paint adhesion to the metal, and produce the best appearance of the finish painted part. The metal must be free of rust, as paint will not stick to rust, and the rust will eventually bubble under the paint over time. I use a simple four step process to clean all of my parts when going back to bare metal.  Once you get into the habit of following this process each and every time, it will become second nature to perform and you will begin to produce your best painting results.

Step 1
rnStrip the surface of old metal (parts) with a grinder installed with a wire wheel. Remove all traces of rust and old paint until clean bright metal is exposed on all sides of the part.  If deep pitting exists which cannot be removed with sanding, then electrolysis cleaning will be required (see the section containing Electrolysis Cleaning procedure). If rust-through holes are exposed, welding the holes closed will be required.

Clean the surface of new metal with mineral spirits which is available at any hardware, paint or department store. This will remove all traces of oil and grease left on by the manufacturing process. You can also use a 50/50 mixture of Simple Green and Water to do the same grease removal job (much cheaper). Insure parts are completely dry be fore proceeding to the next step, or use a heat gun to accelerate the process.

Step 2
rnUse a commercial rust remover according to directions if there are any signs of rust on the surface. Paint will not adhere to rust. Even a little bit will ruin the whole project, so don't skip this step. I generally use either Professional Rust - Prep or POR-15 Metal Ready, depending on what I have on hand. Both work equally well and cost about he same.
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rnStep 3
rnUse a coarse grade sandpaper or a wire brush (you can use a wire brush attachment on a drill or grinder as well) and roughen up the surface. Wipe down with a damp rag or sponge to remove all traces of dust. I generally use 220 grit sand paper and surface the entire part, then clean with the simple green mixture to remove dust. Once you get to this step make sure the part is completely dry and get it into primer within one hour. If you cannot take the part from untouched to primer in a single session, don't start the part stripping process. Rust will form immediately after cleaning paint and rust off the part. If the surface is not prepped and primed in short order, you are waisting your time.
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rnStep 4
rnPrime your surface with a primer made specifically for metals. Any automotive spray primer can be used. For the Wheelhorse colors red and linen, I normally use Rust-Oleum Rusty Red metal primer and Rust-Oleum Automotive gray metal primer. Both in the sandable versions. I only use the hard primers (ones with a paint like surface when dried) for special circumstances. You can find these at most paint and hardware stores and all businesses that cater to the industrial market. Wally World is also a good bet. Now your metal surface is ready for painting. Be sure to use paint that is specifically formulated for metal paint.