Restoring and modifying classic cars is a dirty business. Road grime, dirt, leaves, and moisture all leave a lasting effect in the pockets and channels on any vehicle in the form of rust. The key to any restoration is the foundation: start with good, clean metal and build up from there. This often means cutting out the rotted rusty bits and replacing them with good metal. Along with that, you often need to weld to metal that likely has some light rust and pitting. The problem is that if you just weld your patch to rusty metal without prep, the rust will come right back.
Removing rust can be tricky, but there is a way to do it without spending a fortune on blasting. POR-15 metal preparation products are the best way to quickly dissolve rust and protect your fresh repair. Not only is clean rust-free metal important for a good repair, but you also need to protect the fresh welds. Welding heats metal to very high temperatures, which invites moisture from the air to invade the metal. Within minutes, a fresh weld will begin to rust. While you dress the welds with a grinder on the outside, this does nothing for the backside of the weld. Automotive repairs often involve welding on panels that have no access to the back side or lap joints, so those areas are just exposed forever to the atmosphere. Without some sort of protection, the rust will always come back in 3 to 5 years.
The secret to protecting these is weld-thru primer. Formulated with high zinc content, POR-15 weld-thru primer sprays on with an aerosol can, dries in about 30-minutes, and provides lasting protection without a topcoat. When you weld a panel with this specialty primer, the heat vaporizes the coating. As the weld begins to cool, the vaporized zinc reforms onto the weld, creating a moisture-resistant barrier that keeps the new welds clean and protected from rust. This galvanizing process works great for any weld, but it is absolutely critical for any lap joint or panel without full access to all sides.
Prepare The Metal
Using POR-15 weld-thru primer is easy, however there is a multi-step process to get the best results. First, clean the metal with a wire brush or Scotch-Brite pad to remove dirt, old paint, and loose rust. Then the area is cleaned with POR-15 Cleaner Degreaser. Mixed in a 4:1 ratio with hot water, spray the cleaner directly onto the metal, agitate surface with a brush, and rinsed with clean water. The metal must be bone dry before moving to the next step: Metal Prep.
Dissolve The Rust
POR-15 Metal Prep dissolves light rust and etches bare and rusty metal. Rusty metal can look relatively clean, but that nasty oxidation hides in the microscopic pores of the metal. Metal Prep attacks the rust, dissolving it away and leaving behind a zinc phosphate coating that protects the metal from future rust. It also etches the metal, which is to say that it uses an acid to open up the pores of the metal, giving any topcoat a rough surface (microscopically, you can’t feel it) to bond to. The beauty of Metal Prep is that it is reusable, so a quart goes a long way. It is water-based and contains no petroleum products or chlorine, making it safe to weld through.
Metal Prep can be brushed or sprayed on, as well as used as a soak. The area being prepped must stay wet for 20-30 minutes and not allowed to dry. It is even easier than it sounds. After the wait time, rinse with water and wipe dry. The panel must be fully dry before the final step. You will not see a dramatic color change, in fact, the metal may still look rust colored, but rest assured, the metal is protected and ready for coating. This works for clean fresh metal, as well as the rusty crusty stuff.
Prime Time
Shake the can well to distribute the solids throughout the primer, then spray the repair area. One to two medium coats are sufficient. POR-15 Weld-Thru Primer dries in about 30 minutes and is moisture-resistant in 15 minutes. You don’t have to complete the project immediately; the primer will protect the metal for a long time if necessary. You may get some additional pop and sizzle when welding through the primer, but this is not contamination, it is part of the process.
Not only does this primer protect those fresh welds, but it also reduces heat in the weld zone to limit warping and welding spatter. It is compatible with most types of welding, including MIG, TIG, SMAW (stick), and resistance (spot welding).
Once prepped and coated, the metal is ready for repair. There is nothing else you need to do to get the protection you need. There is no need to waste the primer; you only need about two inches around the weld joint to get full protection. This primer can be applied over POR-15 Rust Preventative and is compatible with most topcoats. Visit POR15.com to learn more about these and other products to help bring your project back to life.