📅 Published October 11, 2026🔄 Updated October 14, 2026✍️ KJ Lee, Ace Auto Body Inc.
Introduction
In Part 1, we inspected a 2023 Kia Forte that someone had "fixed" with spray cans, agreed on a plan with the owner, and took the damaged parts off the car. Before we start the bodywork in Part 3, this post walks through the tools and materials we will use, so the next post is easy to follow.
Everything in the photos below is from our own shop, Ace Auto Body Inc. in Hackensack, NJ. If you know what these tools do, you will also know what a proper repair involves, whether you do the work yourself or hire a shop.
Part 2 at a glance.
Chart 1. The order of the work in Part 3.
1. The DA Sander, Sandpaper, and Blocks
DA stands for dual action. The pad spins and, at the same time, moves in a small random orbit. Because the motion is random, it removes material fast without leaving deep straight scratches. It is the main power tool in any body shop. Ours run on air, so they need a compressor and clean, dry air.
We use the DA for
Stripping old paint and failed repairs, sanding to bare metal, feather edging, shaping cured filler, sanding primer on big flat areas, and fine finishing.
We do NOT use it on
Tight edges, sharp body lines, and small curves. A power sander can round a body line or burn through paint in seconds. Those spots get sanded by hand.
1Two air DA sanders. One is a Mirka; the other runs a yellow pad.
2Paper on the pad. Hook-and-loop backing, with holes that let the dust get pulled away.
3Boxed discs, P100 to P220, sorted by grit on the shelf.
4Rolls in P220 and P320, including a purple 3M Cubitron II roll.
5A P320 disc over a gray foam interface pad. The soft pad helps the finer grits follow the panel.
6Hand blocks: long and short Dura-Block and 3M blocks. A block cuts the high spots; fingers just follow the waves.
Reading Sandpaper Grit
Grit is a number. A lower number is coarser and removes more; a higher number is finer and leaves a smoother surface. The "P" means the European (FEPA) standard used on most auto body paper. The one rule that matters most: move up through the grits step by step. Jump from coarse to very fine, and the deep scratches stay in the panel and show up under the paint.
Chart 2. Which grit for which job.
| Grit | Typical use on a DA sander |
|---|
| P40 | Heavy removal: thick old paint, rust, bad filler. Very aggressive; use with care. |
| P80 | Paint down to metal, rough shaping of filler. The usual starting grit for a dent. |
| P120 | Refine the filler shape and remove P80 scratches. |
| P150–P180 | Final filler shaping and feather edging (3M’s filler guide lists P80 to P180). |
| P220 | Sand glazing putty and start primer prep. |
| P320 | Final grit before primer; also common for sanding primer before color. |
Blocks and Guide Coat
WHY A BLOCK, EVERY TIME
Sand with your fingers and the paper follows the waves. Sand with a block and it cuts the high spots down to the low ones. Use long flexible blocks on doors and hoods, short rubber blocks on small or curved areas, and foam blocks with finer paper on contours. Sand in a cross pattern so the block does not dig a groove, and keep the block face clean.
GUIDE COAT: SEE WHAT IS NOT FLAT
A guide coat is a thin contrasting layer, in our shop black dry guide coat, wiped over sanded filler or primer. When you block sand, it stays in the low spots and disappears from the high spots. Repeat until the black sands off evenly. It is cheap and it saves hours.
2. Body Filler, Glazing Putty, and Guide Coat
Body filler is a two-part material mixed with a small amount of hardener. We mix it on a clean mixing board, never on the panel, and spread it with a plastic spreader in thin layers. Thick filler does not last: it can crack and shrink. The better the metal is reshaped first, the less filler the panel needs.
Glazing putty (also called spot putty) is thinner. It fills the pinholes and fine scratches left after the filler is sanded, and it is the last correction before primer.
13M Platinum Plus filler next to a metal-reinforced filler on the shelf.
2The mixing board. Old filler on one side, clean cardboard on the other: mix on something clean.
3Mixing filler with yellow and orange plastic spreaders.
4Glazing putty: pouch, hardener tube, mixed putty, and a spreader.
5Evercoat 440 Express, a micro-pinhole eliminator. The label says no sanding is required.
6Black dry guide coat (100 g) with its applicator.
Chart 3. Body filler vs. glazing putty.
3. Finishing, Scuffing, and Masking
Wet sanding uses waterproof paper and water. The water carries the residue away and keeps the paper from clogging, so the scratches are finer and more even. Some of it happens before paint (P400 to P600 on primer); most of it happens after the clear coat, in Part 4.
| Grit | Typical use when wet sanding |
|---|
| P400 | Sand primer before color; can also flatten a rough surface. |
| P600 | Sand primer or scuff the surface before painting. |
| P1000 | Level orange peel, dust, and small flaws in cured clear coat. |
| P1500 | Remove P1000 scratches and prepare the clear for polishing. |
| P2000 | Final fine sanding before compounding and polishing. |
CAREFUL WITH CLEAR COAT
Clear coat is thin. On the finishing discs, use light pressure, keep the sander moving, and stay away from edges and body lines, where the clear is thinnest. Sand through it and the area has to be repainted.
Red scuff pad
The coarser pad. We use it to scuff old paint or clear coat before refinishing.
Gray scuff pad
The finer pad, for fine scuffing and blend areas. Some gray ultra-fine pads are rated around 1200 grit.
Scuffing paste
A mild abrasive paste used with a pad to scuff tight areas and body lines evenly by hand.
Grit ratings of scuff pads differ by brand, so read the package. Before any primer or paint goes on, everything that should stay clean is masked with tape and paper.
1Sunmight finishing film discs, 6 inch, in 600 and 1000 grit.
2The masking paper cart: rolls of paper with tape, ready to go.
Which Tool for Which Job
| Job | Tool or material |
|---|
| Remove paint, rust, or old filler | DA sander, P40–P80 |
| Shape cured filler | P80–P180, DA and block |
| Find high and low spots | Dry guide coat and a sanding block |
| Fill pinholes and fine scratches | Glazing putty, sanded P180–P220 |
| Sand primer before color | P320–P400, block and DA |
| Reach edges and jambs | Scuff pad or scuffing paste |
| Level orange peel in clear | Wet sand P1000, then P1500 and P2000 |
| Bring back the gloss | Compound and polish |
Common Mistakes
Skipping grits
Deep scratches from coarse paper show through the paint.
Too much filler
Reshape the metal first. Thick filler cracks and shrinks later.
No block
Sanding with your hand leaves the panel wavy.
No guide coat
You cannot see the low spots.
Dirty surface
Clean before you sand, every time.
DA on edges
Aggressive sanding on edges and body lines burns through paint.
Shop Tips
FROM THE SHOP FLOOR
- ✓Fix the metal first. Panel recovery before body filler gives a repair that lasts.
- ✓Use a block, and use it often. Your hand finds the low spots only after the block shows you where they are.
- ✓Do not skip the guide coat. It is cheap and it saves hours.
- ✓Keep sandpaper organized by grit. One coarse disc in a fine box can ruin a panel.
NEXT IN THE SERIES
In Part 3, we use these tools and materials on the Forte’s removed parts, the front doors and the bumper, from the first layer of filler to finished primer.
Review Questions (with Answers)
1What does "dual action" mean?SHOW ANSWER ▾
2Is P80 coarser or finer than P220?SHOW ANSWER ▾
3Why not jump from P80 straight to P320?SHOW ANSWER ▾
4What does a guide coat show?SHOW ANSWER ▾
5Why is filler applied in thin layers?SHOW ANSWER ▾
6What does glazing putty do?SHOW ANSWER ▾
7When do you use a scuff pad instead of a sander?SHOW ANSWER ▾
Frequently Asked Questions (FAQ)
Q
What is a DA sander used for?
ARemoving paint and old repairs, shaping body filler, feather edging, and sanding primer on larger flat areas.
Q
What sandpaper grit should I use on body filler?
AStart around P80 for the rough shape, then P120 and P180. Follow the filler maker’s guide.
Q
What is the difference between a red and a gray scuff pad?
ARed is coarser, for scuffing old paint or clear; gray is finer, for fine scuffing and blend areas. Ratings vary by brand.
Q
When do you use P1000 and finer?
AAfter the clear coat has cured, to level orange peel and dust before polishing. Keep away from edges.
Q
Do I need all of these tools for a small repair at home?
ANo. A sanding block, a few grits of paper, filler, glazing putty, and masking are enough. A DA sander saves time on bigger areas.
Glossary
DA (dual action)
A sander whose pad spins and orbits at the same time
Grit
The number that tells how coarse sandpaper is; lower is coarser
Feather edge
Sanding the edge of the remaining paint smooth, with no step
Guide coat
A thin contrasting layer that shows low spots when sanding
Body filler
A two-part material used in thin layers to shape low areas
Glazing putty
A thin filler for pinholes and fine scratches
Interface pad
A soft foam pad between the sander and the disc
Wet sanding
Sanding with waterproof paper and water for a fine finish
Scuff pad
A nonwoven abrasive pad that dulls a surface so paint can grip
Panel recovery
Reshaping the metal toward its original form before filler
Sources and Related Reading
Previous and Next Posts
About the Author
KJABOUT THE AUTHOR
KJ Lee & the team at Ace Auto Body Inc.
This series is written by the team at Ace Auto Body Inc. in Hackensack, New Jersey, an auto body repair and paint shop, with about 20 years of experience behind KJ Lee's work. We share real repairs from our shop, with our own photos, so car owners can understand what a proper repair involves. Read more on the About page.
≈ 20 yrs
auto body & paint experience
Hackensack, NJ
Ace Auto Body Inc.
Real repairs
from our shop, our own diagrams
Read our story →
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