Keeping the Rust Off: How to Protect Your Underbody from Salt and Red Dust

Give the whole underside a massive blast with water. You need to get every bit of mud, sand, and salt out. If you've been in the red dirt, keep spraying until the water runs clear. It might take longer than you think.

Spray your degreaser liberally over the greasy bits (engine crossmember, gearbox area). Let it dwell for 10 minutes (don't let it dry!) and scrub the thick stuff with a stiff brush.

This is the part most people mess up. You cannot apply protection to a wet chassis. Leave the car in the sun for a few hours, or better yet, overnight. If you're in a rush, use a leaf blower to kick the water out of the box sections.

Get under there with your light. We're looking for 'cancer' (structural rust) versus surface rust. Surface rust is fine; we can work with that.

Anywhere you see bubbling or loose flakes, get stuck in with the wire brush. You don't need to get to shiny metal, just knock off anything that's loose. If you leave loose rust, your sealant will just peel off like a bad scab.

Don't be a cowboy. Cover your brake discs, exhaust (especially the catalytic converter), and any rubber belts. You don't want lanolin on your brakes, that's a one-way ticket into the back of a bus.

If you've got heavy surface rust, hit it with a converter like Tanic. It turns the rust into a black, stable base. Honestly, I'd only do this on older rigs; newer ones usually just need a clean and seal.

If it's a bit chilly or you're using a thick lanolin, stick the can in a bucket of warm water for 10 minutes. It'll spray much smoother and creep into the joins better.

This is crucial. Use a long extension wand to spray inside the chassis rails. This is where cars rot from the inside out. Give it a good gutful until it starts dripping out the drain holes.

Start from the front and work back. Use long, even strokes. You're looking for a consistent wet look, not massive runs. I reckon two thin coats are always better than one thick, messy one.

Focus on spring hangers, body mounts, and the area above the spare tyre. A customer once brought in a Prado that looked mint, but the spare tyre winch was so rusted it had to be cut off because he'd never sprayed up there.

Check your paintwork. If you've got lanolin or wax on the guards, wipe it off now with a microfiber and some wax remover. It's a pain to get off once it sets in the sun.

Wait 20 minutes for the product to 'tack up' and then go back over with your light. Fill in any patches you missed. It's easy to miss the top side of the fuel tank or the diff housing.