Auto body tools: names, pictures and what each one is used for

The process, and why the order cannot be shuffled

Bodywork goes wrong when stages get skipped or overlapped. The sequence is fixed: get the metal as close to shape as possible, treat any rust back to bare clean steel, fill only the last millimetre, shape the filler, prime, block it flat, then paint.

The reason is that every stage magnifies the one before it. Filler cannot fix a panel that is still the wrong shape, it just makes a thick soft patch that cracks. Primer will not hide a sanding scratch, it will show it. And paint, especially metallic, reveals every flat spot and every ripple you could not see in bare metal.

The single most useful habit is to stop looking at the panel and start feeling it, with a flat hand and with a guide coat.

Metal first, filler last

Get the shape back with hammers, dollies or a puller. Filler is for the final millimetre, never for the shape.

Thin filler, built in layers

Thick filler traps air, cracks and eventually lets go of the panel. Several thin coats, each shaped before the next.

Use a guide coat

A light mist of contrast colour, then sand. What remains is a low spot. It shows what your eye cannot.

Feel it with a flat hand

Your palm detects a ripple far better than your eye does. Flat hand, light pressure, sweep across the repair.

Work through the grits in order

Every skipped grit leaves scratches the next one cannot remove, and primer then shows them clearly.

Check under a light that rakes the panel

Overhead light hides waves. A light along the surface reveals exactly what the finished paint will.

Rust, and the only repair that lasts

Rust is not a surface problem. By the time it shows, it is in the metal, and covering it with filler simply hides it while it continues underneath. A filled rust patch reappears, usually within two winters, and looks worse than before.

The only lasting repair is to remove all of it. Cut out or grind back until every trace of brown is gone, treat the surrounding metal, then weld or bond in new steel if there is a hole. Filler over sound bare metal is fine; filler over rust is a delay, not a repair.

Cut back to bright clean steel

All of it. Rust left under a repair keeps going, and it will come back through the paint.

A hole needs metal, not filler

Anything you can push through wants a welded or bonded patch. Filler across a hole has nothing to hold on to.

Treat the surrounding area

Rust converter or an etch primer on the bare metal around the repair, before anything covers it.

Seal the back of the panel too

Most rust starts from behind, in a trapped damp cavity. Repairing only the visible side is repairing the symptom.

Check the structure, not just the skin

Rust in a sill, chassis rail or suspension mount is a safety issue and a test failure, not a cosmetic one.

Spraying, and what actually decides the finish

Paint problems are almost always preparation problems or environment problems, not gun problems. A cheap gun over good preparation in a clean warm space beats an expensive gun over poor preparation in a cold dusty garage.

The two environmental factors that matter are dust and temperature. Dust lands in wet paint and stays there. Cold slows the cure, changes how the paint flows and causes runs and blooming. Neither is fixed by technique.

This is also the point where the health risk becomes serious. Two pack paints contain isocyanates, and they need an air fed respirator rather than a cartridge mask. This is genuinely different from ordinary spray painting.

Two pack paint needs air fed breathing protection

Isocyanates cause occupational asthma, and it is permanent. A cartridge mask is not adequate protection for this.

Control the dust before you mix anything

Damp the floor, wipe everything down, and let it settle. Dust in wet paint is a flatting and polishing job.

Warm the panel and the paint

Cold paint will not flow out, and the finish blooms or runs. Around 20 degrees for both, and stable.

Tack cloth immediately before spraying

The last wipe catches the dust that landed while you masked. It costs nothing and it saves the coat.

Blend rather than stopping at a hard edge

A repair blended out into the panel disappears. A hard edge is visible forever, whatever the colour match.

Practise the gun on something else first

Set the fan, the fluid and the distance on scrap. Learning that on the panel costs you the panel.

What to buy first, in order

Stage one: assessment and small repairs

A body hammer, a dolly, a sanding block set, abrasive paper in a range of grits, a filler spreader, a wire brush, a work light and eye protection.

Stage two: shaping properly

A dual action sander, a long flat file board, a slapper, a pick hammer, a panel gauge and a guide coat aerosol.

Stage three: rust and panel work

An angle grinder with cutting and stripping discs, a MIG welder or panel bonding kit, a spot weld cutter, tin snips and a hole punch flanger.

Stage four: paint

A compressor with a water trap and regulator, a spray gun, masking materials, an air fed respirator, and polishing gear for finishing.

Mistakes that show in the paint

Filling over rust

It comes back through, usually within two winters, and looks worse than the original damage.

Using filler to make the shape

Thick filler cracks, absorbs moisture and eventually lets go. Get the metal right first.

Skipping grits when sanding

Coarse scratches survive under fine paper and then primer highlights them perfectly.

Sanding with your fingers instead of a block

Fingers create hollows and ripples. Blocks and boards are what make a panel flat.

Spraying two pack in a cartridge mask

Isocyanate exposure causes permanent occupational asthma. This is the most serious risk on the page.

Painting in a cold or dusty space

Cold causes runs and blooming, dust means flatting and polishing. Neither is a technique problem.

Stopping the paint at a panel edge

A hard edge in the middle of a panel is visible from any angle. Blend it out or take the panel to a natural break.

Judging the repair under overhead light

It hides waves that daylight and raking light show immediately. Check it the way the customer will see it.

Looking after auto body tools

Clean the spray gun immediately

Dried paint in the nozzle or needle changes the pattern permanently. Strip and clean it every single time.

Drain the compressor and the water trap

Water and oil in the air line lands in the paint as blisters and fisheyes. Drain it before every session.

Keep hammer faces polished

A hammer face that has picked up a nick prints that nick into the panel with every blow.

Do not let filler set on a spreader

A ragged spreader edge leaves ridges. They cost almost nothing, so replace them rather than fighting them.

Store abrasives dry and flat

Damp paper clogs instantly and curled paper cannot follow a block. Both waste more than they cost.

Cap the paint and stir tins properly

A skinned tin drops flakes into the mix that turn into visible bits in the finish.

Frequently asked questions

What auto body tools do I need to start?

A body hammer, a dolly, a set of sanding blocks, abrasive paper across a range of grits, filler and spreaders, a wire brush, a good work light and eye protection. That covers assessing damage and repairing a dent or small rust patch properly.

What is the difference between auto body tools and mechanic tools?

Mechanic tools turn fasteners and diagnose systems. Auto body tools shape metal and produce a finish: hammers and dollies, files, sanders, filler tools, masking and spray equipment. There is almost no overlap beyond a grinder and a drill.

Can I just fill over rust?

No. Rust continues under filler and comes back through the paint, usually within two winters, looking worse than before. The metal has to be cut or ground back until every trace is gone, and a hole needs a welded or bonded patch.

What is a dolly and why do I need one?

A shaped steel block held behind the panel while you work the front with a hammer. Without a dolly you are stretching the metal rather than shaping it, which makes the dent worse and harder to fix.

How thick can body filler be?

As thin as you can manage, built in layers, and never used to create the shape. Thick filler traps air, cracks and eventually releases from the panel. Get the metal close first, then use filler for the last millimetre.

What is a guide coat?

A light mist of contrasting colour sprayed over a repair before sanding. As you sand, the guide coat stays in the low spots and disappears from the high ones, showing you exactly where the panel is not flat.

Why do I need to sand through the grits in order?

Each grit removes the scratches left by the previous one. Skip a step and the coarse scratches survive, and primer highlights them rather than hiding them. The sequence is what produces a flat scratch free surface.

Is spraying two pack paint at home safe?

Not without air fed breathing protection. Two pack paints contain isocyanates, which cause permanent occupational asthma, and a cartridge respirator does not provide adequate protection. This is the most serious health risk in bodywork.

Why does my paint look dull or blotchy?

Commonly a cold panel or cold paint, which stops it flowing out, or moisture in the air line, or spraying too dry. Warm the panel and the paint to around 20 degrees, drain the water trap and check your gun distance.

What causes fisheyes in fresh paint?

Contamination, usually silicone or oil. It can come from polish residue on the panel, from your hands, or from oil in the compressed air. Degrease properly with panel wipe and fit a decent water and oil trap.

Do I need a compressor for bodywork?

For spraying, effectively yes, unless you use aerosols for a small repair. Air tools also do most of the sanding. Size it on air consumption rather than tank size, since a sander uses far more air than people expect.

How do I blend a repair into the surrounding paint?

Spray the colour progressively lighter as you move away from the repair, then clear the whole panel to a natural edge. Stopping colour or clear at a hard line in the middle of a panel leaves a mark visible from any angle.