2023 Kia Forte GT-Line Repair, Part 3: Body Filler, Putty, and Primer
Ace Auto Body Inc. · Hackensack, NJBlogger preview
Introduction
In Part 1, we inspected a Kia Forte that had been "fixed" with spray cans and took the damaged parts off. In Part 2, we went through the tools and materials. Now we use them. This post follows the repair from the first sanding pass to the first coat of primer: sanding out the old repair, body filler and glazing putty, block sanding, masking, and priming.
This is the stage where the car actually gets fixed, and where a shortcut shows up later as a wavy panel or a crack in the paint.
Part 3 at a glance.
Chart 1. Where the bodywork happens.
Step 1: Sand Out the Old Repair
The first job is to sand out the old putty and body filler from the street repair. Once it is gone, the real damage, like a door ding, is easy to see. You cannot repair what you cannot see, and you cannot trust filler when you do not know how the metal under it was done.
Step 2: Dull the Clear Coat Where No Color Goes On
The areas that will not get color still have their original, glossy clear coat. We take the gloss off with a P1000 disc on the DA or with a gray scuff pad, so the next layer can grip. On the bumper it is the same idea: the DA on the big surfaces and a scuff pad on the edges and curves.
Sanding dust is chemical. Body filler dust is not like wood dust: it can irritate the lungs, and primer and paint add vapors on top of that. A half-mask respirator with the right cartridges, eye protection, and gloves are not optional.
A personal note: the dust and the paint smell are a big reason many people quit body shop work soon after they start. At first, the smell feels like it goes straight into your head. It gets easier, but only if you protect yourself and keep the shop ventilated.
Step 3: Clean, Then Apply Body Filler
Before any filler goes on, we wipe the area with PREP-ALL (a wax and grease remover). Filler does not bond to a dirty or oily surface. Then the product depends on the depth of the damage: body filler first for deep damage, in thin layers built up only as much as the shape needs, and glazing putty on top to fill pinholes and fine scratches.
We never mix on the panel. We mix on a mixing pad (we tear off the top sheet and start clean) or a piece of cardboard, and spread with plastic spreaders.
Doors take a shock every time they are slammed, and the thicker the filler, the higher the risk of a crack later. On this Forte, the filler ended up a little over 1/4 inch, under 1/2 inch. Past about 1/2 inch, cracking becomes much more likely, so we explain the risk to the owner and get their OK before the work.
Step 4: Shape It: DA First, Then a Big Block
Once the filler has cured, we shape it in two stages:
- DA sander first to take off the thick, rough areas fast.
- A large hand block next, with P120, then P180, then P220. The block cuts the high spots and leaves the low ones, so the panel comes out flat instead of wavy.
Direction matters. We push the block across the repair from different sides toward the center, so the surface stays even and no groove forms in one direction.
Blue arrows: we push the block in from every side toward the center. Kept large so you can see the pattern.
The Front Bumper Is Different
A plastic bumper gets different treatment. On this Forte’s bumper, we used only the DA sander and then finished by hand. The hand finish matters: it removes the scratches the repair leaves behind. Skip it and the bumper looks fine until primer goes on, and then every scratch shows. We marked the area to fix in blue first, so we only worked where it was needed.
Step 5: Finish With Glazing Putty
When the body filler is done, we finish with glazing putty. It fills the last pinholes and scratches and makes the primer easy to spray, because the surface is already smooth. We wipe with PREP-ALL again before every application.
Chart 2. Seven steps from old filler to primer.
Step 6: Mask With Primer Paper
When all the bodywork is done, we cover everything that must not get overspray, like the door panel and the glass, with paper.
The paper in these photos is for primer. In the paint booth, we use clear paper for the clear coat. If clear coat gets on primer paper, it soaks into the paper and can stick to the car. Fixing that means more wet sanding, and a small job turns into a big one. Use the paper that matches the job.
Step 7: Prime
We spray the first coat of primer over the body filler and look for marks. If any show, we spray a second coat, and the primer covers what is left from the bodywork.
Chart 3. How long primer dries in our shop.
Primer that is still soft can shrink after it is painted, so we do not rush it. This is also where the painter’s skill shows: the panel is standing up, and the painter has to put on enough primer to cover the marks without letting it run. That takes practice, which is why a good painter is worth a lot in a shop.
Who Does What in a Body Shop
Common Mistakes
Shop Tips
- ✓See the damage first. Take the old repair off before starting the new one.
- ✓Think in layers. Thin filler, thin putty, then primer.
- ✓Block sand, and change direction. A flat panel comes from the block, not your fingers.
- ✓Give the primer time. About 4 hours in summer, overnight in winter, and each product is different.
- ✓Protect yourself. A respirator is cheaper than a lung problem.
In Part 4, we get the car ready for paint with wet sanding, scuffing, masking, and color matching, and then we paint it.
Frequently Asked Questions (FAQ)
Sources and Related Reading
Previous and Next Posts
About the Author
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.
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