Filler, feather edges, primer and paint prep — the DA sander does all of it. Here is how to choose one and use it like a body shop would.
⚡ The Short Answer
For auto bodywork, a geared air DA sander with a 6″ pad is the body shop standard — light enough to hold against a panel all day, and the geared drive keeps cutting when you lean into filler. Pair it with a 3″ DA for edges, jambs and small repairs.
No compressor? An electric random orbital will do a full respray prep perfectly well. It is heavier, but it costs nothing extra to run and you will not be waiting on a compressor to catch up.
The tool matters less than two habits: use a guide coat, and never skip grits.
Bodywork is unforgiving in a way woodworking is not. A flaw you can barely feel with your fingertips becomes obvious the moment gloss paint reflects a straight line across it. Every wave, every scratch, every low spot shows.
The good news is that flat panels are mostly technique, not talent. Body shops get consistent results because they follow a repeatable process — the right grit at each stage, a guide coat to reveal the truth, and a light touch. This guide walks through that process and the sanders that suit each part of it.
Why Bodywork Needs a DA Specifically
A rotary sander spins in one direction, so every abrasive grain follows a circular track. On bare metal that is invisible. Under primer it is faint. Under gloss colour and clear coat it becomes a swirl pattern that catches every light source, and no amount of polishing fully removes it once it is sealed under paint.
A dual action sander spins and orbits at the same time, so the scratch pattern is random rather than circular. Random scratches disappear under primer instead of telegraphing through it.
That is the entire reason body shops use DA sanders. It is not about speed — a rotary removes filler faster. It is about what the surface looks like three stages later.
Where the DA does its work in a panel repair:
- Shaping filler after it cures, knocking the high spots down to the panel line
- Levelling the filler so it blends invisibly into the surrounding metal
- Feather edging the paint around the repair so there is no step
- Scuffing existing paint so primer and colour can grip
- Flatting primer before colour goes on
- Polishing afterwards, with a foam pad instead of abrasive
🚗 The body shop truth: a paint job is 90% preparation. The spray gun just shows everyone how good your sanding was.
Pad Sizes and What Each Is For
Most people buy one sander and struggle with everything it cannot reach. Serious panel work really wants two.
| Pad size | Best for | Struggles with |
|---|---|---|
| 6 inch | Doors, bonnets, roofs, wings — large flat panels | Curves, jambs, tight radius areas |
| 5 inch | General all-round work, best disc availability | Very tight contours |
| 3 inch | Edges, jambs, pillars, small dent repairs, spot work | Anything large — far too slow |
| Long board (hand) | Checking and levelling long flat panels | Not powered — slow but unbeatable for flatness |
A 6″ DA covers a bonnet quickly, but the moment you reach a wheel arch or a door shut, it becomes a liability — the pad overhangs, tips onto its edge, and cuts through the paint on the high point. That is exactly where the 3″ earns its money.
The hand long board deserves a mention too. Powered sanders follow whatever shape is already there. A long flat board bridges low spots and only cuts the highs, which is how professionals get genuinely flat panels rather than smooth-but-wavy ones.
✅ Buy the 3″ second, not never. Most people regret trying to do detailed areas with a big pad long before they regret spending on a small one.
Air vs Electric for Panel Work
In a professional shop this is not a debate — air wins because the tools are light, cheap and run all day without heating up. When you are holding a sander against a vertical door for an hour, weight is the deciding factor.
At home, the maths changes completely. A DA sander typically wants around 5–10 CFM sustained at 90 PSI. That is a serious compressor, not a portable pancake unit. If you buy an air sander and a small compressor, you will spend the job waiting for pressure to recover.
Choose air if: you already own a capable compressor, you do bodywork regularly, or you value the light weight over hours of work.
Choose electric if: this is a home restoration or occasional repair, you do not want to invest in compressed air, or you also want the sander for woodworking.
An electric random orbital will produce a professional result on a car. It is heavier and you will feel it, but the finish is down to grit sequence and technique, not power source.
⚠️ Check sustained CFM, not peak. Compressor boxes advertise peak or short-burst figures. Sanders need continuous airflow. Mismatching here is the most common and most expensive air-tool regret.
Our Picks
Selected on published specifications and owner ratings rather than hands-on testing.
Ingersoll Rand 328B Dual-Action Geared Air Sander
Best for Filler Work★★★★★ 4.7 out of 5 — professional standard
The geared drive is what separates this from a budget DA. On a free-spinning sander, pressing into filler slows or stops the orbit — and the moment the orbit stops you are effectively using a rotary sander, leaving swirls. A geared DA drives the orbit positively, so it keeps cutting the random pattern even under hand pressure.
- ✅ Keeps orbiting under pressure — the key to swirl-free filler work
- ✅ Light in the hand for long vertical panel sessions
- ✅ Shop-grade durability
- ⚠️ Needs a genuine compressor, not a portable unit
- ⚠️ Best for: regular bodywork with existing shop air
Price and availability change often — the button shows the live Amazon price.
Ingersoll Rand 311G 6-Inch Edge Series Dual Action Air Sander
Best 6″ for Big Panels★★★★☆ 4.2 out of 5 — large panel coverage
A 6-inch pad is what body shops reach for on bonnets, roofs and doors, simply because it covers ground faster and bridges small irregularities better than a 5″. If your work is mostly large panels rather than detail areas, the extra pad diameter saves real time across a full respray prep.
- ✅ Covers large flat panels quickly
- ✅ Bigger pad bridges minor waves better than a small one
- ⚠️ Awkward on curves and jambs — pair it with a 3″
- ⚠️ 4.2 rating — solid rather than class-leading
- ⚠️ Best for: bonnets, roofs, doors, full respray preparation
Price and availability change often — the button shows the live Amazon price.
DEWALT Random Orbit Sander, Variable Speed, 5-Inch (DWE6423)
Best Without a Compressor★★★★★ 4.7 out of 5 — home restoration choice
For a home restoration this is the practical answer. 8,000–12,000 OPM variable speed lets you run slow for feather edging and delicate primer flatting, then faster for stripping. The counterweight matters more than it sounds — panel prep means hours of sanding, and vibration is what ends sessions early.
- ✅ No compressor required — the biggest practical advantage for home use
- ✅ Slow speeds for feather edging without burning through paint
- ✅ Doubles as a woodworking sander
- ⚠️ Heavier than air — you will notice on vertical panels
- ⚠️ Best for: home restorations, occasional repairs, dual-purpose use
Price and availability change often — the button shows the live Amazon price.
Comparison
| Model | Power | Pad | Compressor | Best stage |
|---|---|---|---|---|
| Ingersoll Rand 328B | Air, geared | — | Required | Filler shaping and levelling |
| Ingersoll Rand 311G | Air | 6″ | Required | Large panels, full prep |
| Ingersoll Rand 311A | Air, angle | — | Required | Awkward angles, tight areas |
| DEWALT DWE6423 | Corded electric | 5″ | Not needed | Home restoration, all stages |
| Makita XOB01Z | 18V battery | 5″ | Not needed | Awkward positions, no cables |
💬 Affiliate disclosure: as an Amazon Associate, DetailSanderGuide may earn from qualifying purchases. This costs you nothing extra and never changes which tools we recommend.
The Full Bodywork Grit Sequence
This is the part people get wrong. Each grit exists to remove the scratches left by the previous one. Skip a step and the deep scratches stay — and they will appear under paint.
| Stage | Grit | What it does |
|---|---|---|
| Strip to metal | 80 | Removes paint and rust back to bare panel |
| Shape filler | 80 | Knocks cured filler down to rough panel shape |
| Level filler | 120–180 | Blends filler flush into surrounding metal |
| Feather edge | 180–220 | Tapers surrounding paint so there is no step |
| Pre-primer | 220–320 | Final key before primer goes on |
| Flat the primer | 400–600 | Levels primer, usually with a guide coat |
| Pre-colour scuff | 600–800 | Light key so colour grips |
| Post-paint | 1500–3000 wet | Removes dust nibs and orange peel before polishing |
Never jump more than about 100 grit at a time below 400. Going 80 straight to 320 leaves 80-grit scratches that fine paper cannot reach. Our grit progression planner builds the exact ladder for your job.
Guide Coat — The Technique That Changes Everything
If you take one thing from this guide, take this. A guide coat is a light mist of contrasting colour — usually a dark aerosol or a dry powder — sprayed over filler or primer before you sand.
As you sand, the guide coat disappears from the high spots first and stays behind in the low ones. You are no longer guessing whether a panel is flat: you can see it. Sand until the guide coat is completely gone and the surface is genuinely level.
How to use one:
- Sand the filler roughly to shape with 80 grit
- Mist a light, even guide coat over the whole repair — you are not painting it, just dusting it
- Sand with 120–180 on a flat block or the DA
- Dark patches remaining are low spots — they need more filler, not more sanding
- Repeat until the guide coat vanishes evenly across the panel
Professionals use a guide coat on almost every repair. Amateurs skip it, then wonder why the panel looks wavy once it is glossy.
How to Feather an Edge
A feather edge is a smooth taper from bare metal, through primer and paint layers, out to the untouched finish. Get it right and the repair disappears. Get it wrong and you see a visible ring around the repair after painting.
- Start with 180 grit around the damaged area, working outward in a widening circle.
- Keep the pad flat and let it float — pressure digs a step instead of a taper.
- Work outward until each paint layer shows as a distinct visible band, like contour lines on a map.
- Step up to 220–320 and widen the area slightly to soften the transition.
- Run a fingertip across it with your eyes closed. If you can feel any step at all, keep going — paint will not hide it.
Your fingers are far more sensitive than your eyes here. A ridge you cannot see but can feel will absolutely show under gloss.
Common Mistakes and Fixes
1. Pressing hard on filler
Result: the orbit stalls, the tool cuts like a rotary, and swirls appear.
Fix: let it float. Use 80 grit if you need faster removal.
2. Skipping grits to save time
Result: coarse scratches telegraph through primer and colour.
Fix: follow the ladder. It is faster than repainting.
3. No guide coat
Result: a panel that feels smooth but looks wavy under gloss.
Fix: guide coat every filler and primer stage.
4. Sanding through on edges and body lines
Result: bare metal on every high point, which then rusts.
Fix: edges have less pad contact so they cut faster. Ease off deliberately, or mask body lines with tape while flatting.
5. Using a 6″ pad everywhere
Result: gouged jambs and burnt-through arches.
Fix: switch to a 3″ for anything tight or curved.
6. Worn discs
Result: you press harder, which causes mistakes 1 through 5.
Fix: change discs the moment cutting slows. Abrasive is cheap compared to a respray.
7. Filler applied too thick
Result: endless sanding, and filler that cracks later.
Fix: filler is for shaping, not for building. Fix dents with metalwork first, then skim thin.
Safety You Cannot Skip
Bodywork dust is genuinely more hazardous than woodworking dust, and it is worth being blunt about it.
- Body filler dust is fine, sharp and irritating to lungs. A basic paper dust mask is not adequate — use a proper fitted respirator.
- Older vehicles may carry lead-based primers. Vehicles from before the mid-1990s deserve caution and testing.
- Isocyanates in two-pack primers and clear coats are seriously hazardous and require air-fed respiratory protection when spraying — not just a cartridge mask.
- Eye protection always. Sanding throws grit at speed and you are often working at face height.
- Ventilation matters. A closed garage fills with airborne dust quickly.
- Skin — filler dust and primers irritate. Gloves and long sleeves are worth it.
Full precautions are in our dust safety checklist.
Real-World Examples
The repair that showed up in sunlight
A common story: a wing repair looks perfect in the garage, then in direct sun there is a visible halo around it. The cause is almost always feather edging that was not wide enough or not tapered smoothly, so the paint sits over a subtle step. Widening the feather and stepping through the grits properly prevents it entirely.
The bonnet that rippled after paint
Filler feels smooth to the hand but the panel reads wavy once glossy. Hands detect steps well but are poor at detecting long gentle waves. A long flat sanding board bridges the lows and cuts only the highs — this is exactly the job a powered DA cannot do, because it follows whatever shape is already there.
The compressor that ruined a Saturday
Someone buys an air DA for a single door repair and pairs it with a small portable compressor. The sander runs for a few seconds, then slows while the compressor struggles to catch up. Nothing is faulty — sanders simply consume more air than portable units can sustain. For one-off work, electric avoids the problem entirely.
Frequently Asked Questions
What size DA sander is best for auto bodywork?
6 inch for large flat panels like bonnets, roofs and doors — it covers ground faster and bridges minor irregularities. 3 inch for edges, jambs, pillars and small repairs. If you can only buy one, a 5 inch is the best compromise and has the widest disc availability. Most people who do bodywork regularly end up owning a large one and a small one rather than one medium one.
Can I do bodywork with an electric sander instead of air?
Yes. The finish depends on grit sequence and technique, not on the power source. An electric random orbital is heavier and you will feel that on vertical panels, but it needs no compressor, costs nothing extra to run, and doubles as a woodworking sander. Professional shops prefer air because the tools are lighter over an eight-hour day — that is a comfort and duty-cycle decision, not a quality one.
What grit removes car paint?
80 grit strips paint back to bare metal efficiently. For feather edging around a repair rather than full removal, start at 180 and work outward. Be aware that going to bare metal means you must prime promptly — bare steel starts oxidising within hours in humid conditions, and primer will not stick properly over surface rust.
Why does my filler keep showing swirl marks?
You are pressing too hard, which stalls the orbit and turns the DA into a rotary sander. It can also be a worn disc, or a piece of coarse grit trapped under a finer disc from an earlier stage. Ease off completely and let the tool float, fit a fresh disc, and blow the panel clean between every grit change. If it persists on a free-spinning air DA under pressure, a geared model solves it properly.
Do I really need a guide coat?
If you want a flat panel, yes. Your hand cannot reliably detect the long gentle waves that gloss paint reveals instantly. A guide coat costs very little and turns guesswork into something you can see — the dark residue sits in the low spots and vanishes from the highs. Professionals use one on nearly every repair, and it is the single biggest quality difference between amateur and professional panel work.
How much CFM does a DA sander need?
Typically around 5–10 CFM sustained at 90 PSI, which is a substantial requirement. Check your compressor’s continuous rating rather than its advertised peak, and remember sanders run constantly rather than in bursts like a nail gun. If your compressor cannot sustain that, the sander will feel weak and you will spend the job waiting — go electric instead.
Your Bodywork Sanding Checklist
- Respirator, eye protection and gloves on — not just a paper mask
- Compressor CFM checked against the tool, if using air
- Grit ladder planned with no jumps larger than ~100
- Guide coat applied before levelling filler and primer
- Filler shaped at 80, levelled at 120–180
- Feather edge tapered at 180–220, checked by feel not sight
- Pad kept flat and floating — no downward pressure
- 3″ pad used for jambs, arches and body lines
- Panel blown clean between every grit change
- Fresh discs fitted as soon as cutting slows
- Bare metal primed promptly before it can oxidise
- Body lines masked or eased around to avoid burn-through
Final Thoughts
Panel work rewards patience far more than power. The sander matters, but the guide coat and the grit ladder matter more — they are what turn a repair you can see into one you cannot.
If you have shop air, a geared DA and a 3″ for detail work is the classic pairing. If you do not, the DEWALT DWE6423 will take you from stripped metal to polished paint without a compressor in sight.
🔧 What to read next: the wider category is covered in our best DA sanders guide, and for stripping specifically see sanders for car paint removal. Plan grits with the grit progression planner.