How to Polish an Aluminium Bullbar or Bumper to a Mirror Finish

Work Out What You're Starting With

Before touching the aluminium with sandpaper or a polishing wheel, take a proper look at its condition.

For us, the biggest factors in choosing a starting point are generally stone chips and scratches. The worse the damage, the more correction is required before polishing can begin.

Use the following as a general guide.

These are starting guidelines rather than absolute rules. Assess the aluminium in front of you.

AA — New, show truck or previously polished

If the aluminium is new, on a show truck that rarely sees the road, or has previously been polished and is simply dull, don't sand it just because you can. Depending on its condition, no sanding may be required at all.

Possible polishing combinations include:

• Yellow Airway + 439T → Untreated Airway + P14F
• or, depending on the surface, Untreated Airway + 439T
• or Untreated Airway + P14F

before progressing to the finishing stage.

A — Light surface marks

If the aluminium only has light marks, 600 grit may be all that's required before progressing to machine polishing.

B — Stone chips and normal road scratches

For the type of damage commonly found on a working truck, our normal sanding progression is:

C — Hammered

For a heavily scratched, neglected or badly marked bar, we may start at:

In extreme cases an experienced polisher may start as coarse as 80 grit. However:

Sand the Aluminium

For the Highway Shine process, sanding is performed dry.

We use either:

• a variable-speed sander/polisher; or
• a DA sander, which can be more forgiving for someone learning.

When using our variable-speed machine setup, use the appropriate backing pad and interface pad. When using a DA, use the appropriate interface pad with the sanding system. You'll find discs, pads and backing plates in our sanding and surface preparation range.

Sander speed and pressure

With our variable-speed setup, we generally sand at approximately:

This is subject to the rated operating speeds and instructions for the specific machine, backing pad and abrasive system being used.

Use firm, controlled pressure, but don't lean your body weight into the machine. The abrasive and sander should be doing the cutting. You're controlling the machine — not trying to force it through the aluminium.

Excessive pressure generates unnecessary heat, can make sanding inconsistent and places additional load on the sander. Excessive heat and load can also contribute to machine failure.

Most importantly:

Cross-Hatch Your Sanding

Don't repeatedly sand in one direction. Work the surface side-to-side, then up-and-down:

This creates a cross-hatch sanding pattern. Cross-hatching helps achieve even coverage and reduces the chance of leaving deep parallel sanding marks — often referred to as tram lines or train lines.

When should you change grits?

This is one of the hardest parts of sanding and polishing to learn. The basic rule is:

For example, 180 → 320 → 600: the 320-grit stage needs to remove the 180-grit scratches, then the 600-grit stage needs to remove the 320-grit scratches.

Don't move up to the next grit simply because you've gone over the surface once. It will generally take multiple passes and more than one sanding disc to properly complete each stage.

Take your time. Even experienced polishers occasionally miss a deeper sanding mark. If that happens, it may need additional sanding — normally a few more passes with 600 grit will clean it up.

Prepare Your Buffing Wheels

Before using a new buffing wheel, rake it first.

Continue raking your wheels throughout the job whenever they become loaded or caked with compound and aluminium residue. Raking exposes fresh wheel material and helps the wheel continue cutting or finishing effectively. A buffing wheel cleaning rake makes this quick.

Also keep your compounds separated.

If you're not sure which wheel runs with which bar, our wheel and compound guide covers every combination.

Heavy Cut — Red Airway + 439T

For a bullbar or bumper we've finished sanding at 600 grit, our normal heavy-cut combination is:

We generally run this combination at approximately:

Subject to the safe rated operating speed of the wheel and machine.

Rake the wheel before starting. Then apply a good initial charge of 439T to the wheel.

Work in manageable sections

Don't randomly attack the entire bar. Work in sections approximately 2–3 feet across, or whatever size you can comfortably and safely control.

Start at the bottom of the section and slowly work upward. Keep each pass tight against the previous pass.

As the wheel cuts the aluminium, you'll see a black polishing line develop. Watch the black line. Keeping those polishing lines close together helps ensure the entire surface receives a consistent cut. Learning to control the machine and keep the lines tight takes practice.

When to apply more 439T

The polishing line also helps tell you when the wheel needs more compound. When required, briefly touch the 439T bar against the spinning buffing wheel for approximately 1–2 seconds, then return to polishing.

Don't continually overload the wheel with compound.

Cross-Cut the Heavy Cutting Stage

This is an important part of the Highway Shine heavy-cut process.

The Highway Shine heavy-cut pattern is therefore:

Keep watching the black polishing line and apply additional 439T when required.

Refine — Untreated Airway + 439T

To match the standard Highway Shine polishing system, after the Red Heavy Cut wheel we move to:

Subject to the safe operating limits of the equipment.

Because we're continuing to use 439T, we don't need to completely remove the remaining 439T residue before changing wheels.

Work again in manageable sections and keep the polishing lines tight together. However, at this stage our normal process changes slightly:

Let the finer wheel and compound combination continue refining the surface left by the heavy-cut stage.

Clean Before Changing Compounds

If you're changing wheels but keeping the same compound — such as Red + 439T → Untreated + 439T — there's no need to completely clean the remaining compound from the aluminium first.

However, when changing to a different compound, clean the remaining polishing residue from the aluminium before starting the next stage. This reduces the chance of carrying the previous cutting compound into the finishing stage.

A suitable liquid metal polish can be used for this intermediate clean.

Final Finish — Flannel + 480BLF

Once the cutting and refining stages are complete, it's time to bring out the final clarity. Fit a:

This stage runs considerably slower than the cutting stages. We normally use approximately:

Always remain within the safe rated speed of the wheel and machine.

Use light pressure. You're no longer trying to aggressively cut the aluminium.

Work in manageable sections using tight, overlapping vertical passes.

Applying 480BLF

480BLF is generally applied more frequently than 439T. Briefly touch the compound against the spinning flannel wheel for approximately 1 second at a time, then return to polishing.

Again, watch what the wheel is leaving behind. If you begin seeing small black specks or deposits on the aluminium, this can indicate:

• the wheel needs additional compound; or
• the wheel has become loaded and needs to be raked.

P175 for the Extra Finish

For most jobs, Flannel + 480BLF is the final machine-polishing stage.

However, if you're chasing that extra level of clarity for a show-quality finish, follow it with:

Use essentially the same process as 480BLF:

• approximately 1,800–2,000 RPM
• light pressure
• tight vertical passes
• small applications of compound
• rake the wheel when required

Final Cleanup

Once machine polishing is complete, there will normally be some black compound residue remaining on the aluminium. There are two ways we remove it.

After cleaning, thoroughly hose or pressure-clean the bar to remove remaining cleaner and contamination.

Drying the freshly polished aluminium

Dry the aluminium using a:

Gently dry using an up-and-down motion. Don't aggressively rub the freshly polished surface.

You've just spent hours removing scratches. Don't put new ones back in with a dirty towel.

Maintaining a Mirror-Polished Bullbar or Bumper

The easiest polished aluminium to look after is the aluminium you don't allow to deteriorate badly again.

Regular light hand polishing using a maintenance polish such as EZ Red will help maintain the mirror finish before oxidation and staining become severe enough to require another complete machine correction.

Polishing your fuel tanks too? Read our guide to polishing an aluminium truck fuel tank to a mirror finish.

The Highway Shine Bullbar & Bumper Polishing Process

All speeds are approximate and subject to the safe rated operating speeds of your machine, wheels, pads and abrasives.

Real Highway Shine Results

From damaged to mirror finish

This T909 bullbar arrived with extensive scratching as well as physical damage. The damaged area was repaired first. The aluminium was then prepared, sanded and machine polished to restore the mirror finish.

What You'll Need

Everything used in this guide is part of our metal polishing supplies range.