What Causes a Dish-Out
A dish-out happens when you remove more material from the repair area than from the surrounding panel, creating a depression — a shallow bowl shape where the filler sits below the adjacent surface. The sanded filler feels smooth under your hand because your palm conforms to the depression, but under paint, direct sunlight reveals the wave as a light-dark transition that doesn't belong on a flat panel.
Three things cause dish-outs: sanding without a block, using a block that's too small, and applying too much pressure in the center of the repair while neglecting the edges.
The Block Prevents the Problem
A rigid sanding block bridges across the repair area and contacts only the high points. The block can't follow a depression because it's longer than the depression is wide. Each sanding stroke removes material from the high points and leaves the low areas untouched until the entire surface is level. Your fingers, by contrast, follow every contour — high and low — and remove material uniformly, preserving the dished profile instead of correcting it.
The block must be longer than the repair. A 3-inch repair on a door skin requires at least a 6-inch block — double the repair width so the block always contacts undamaged panel surface on both sides of the filler. For a 10-inch repair, use a 16-inch long board. The block bridges; the repair levels.
Block Selection for Filler Work
Long Boards (16–24 Inches)
Use long boards on flat panels — hoods, roofs, door skins, quarter panel flats, deck lids. A Dura-Block AF44A (16-inch flat) or a 24-inch hand file board with adhesive sandpaper spans across most body repairs and produces the flattest results. Sand with the full length of the board in long, overlapping strokes. Short, choppy strokes with a long board defeat its purpose — you're turning a 16-inch bridge into a 4-inch rocker.
Medium Blocks (6–8 Inches)
For smaller repairs or gently curved areas where a long board can't conform, step down to a 6–8-inch rigid block. These blocks still bridge across typical dent repairs while allowing some radius matching on crowned panels. Mirka hand blocks in this size range provide a good grip surface and consistent pressure distribution.
Contour Blocks
For crowned panels (fender tops, quarter panel crowns), use a contour block that matches the panel's curvature. Dura-Block makes convex and concave blocks (AF44C, AF44D) for this purpose. A flat block on a crowned panel creates flats — the block sits on the crown peak and sands it flat while the shoulders of the curve remain untouched.
Sanding Technique That Prevents Dish-Outs
Full-Length Strokes
Move the block across the entire repair area and 4–6 inches beyond both edges of the filler into the surrounding panel. Every stroke must start on bare panel on one side and end on bare panel on the other. Stopping your strokes at the filler boundary concentrates material removal inside the repair — the definition of a dish-out.
X-Pattern Strokes
Alternate sanding direction between passes: diagonal strokes from upper-left to lower-right, then upper-right to lower-left. This X-pattern prevents directional grooves and ensures even material removal across the entire block contact area. Sanding in only one direction creates ridges parallel to the sanding direction that the block rides over without cutting.
Even Pressure
Distribute hand pressure evenly across the full block face. Pressing harder on one end or in the center causes the block to tilt or flex, concentrating material removal in a localized area. If you notice one area of filler sanding faster than the adjacent area, it's higher — not an invitation to press harder elsewhere. Let the block do the leveling; your job is consistent, even pressure and straight tracking.
Frequent Checks
Stop sanding every 30 seconds and verify the surface. Run a straight edge (a steel ruler, a long mixing stick, or a dedicated body straight edge) across the repair in multiple directions. Any daylight between the straight edge and the surface is a high or low spot. High spots need more sanding. Low spots need more filler — not more sanding. Sanding harder on a low spot makes it deeper.
The Guide Coat Check
After the 80-grit shaping pass, apply 3M Dry Guide Coat powder over the entire repair and transition area. Sand with 120 grit on your block. The guide coat reveals the truth:
Guide coat clears evenly: Surface is flat. Continue to 180 grit.
Guide coat remains in the center, clears on edges: You have a dish-out. The center is lower than the perimeter. Do not sand more — add a thin skim coat of filler over the depressed area, cure, re-guide coat, and re-block.
Guide coat remains on the edges, clears in the center: The filler crown is still higher than the surrounding panel. Continue blocking with even, full-length strokes until the guide coat clears uniformly.
Grit Progression to Prevent Dish-Outs
Each grit step removes less material per stroke than the previous one, reducing the risk of over-sanding. The progression should be 80 → 120 → 180 for filler work.
At 80 grit, you're doing the heavy shaping. This is where dish-outs start — aggressive grit removes material fast, and a moment of uneven pressure creates a depression. Use the block and check frequently. At 120, you're refining — removing 80-grit scratches and fine-tuning the transition from filler to panel. At 180, you're finishing — establishing the scratch pattern for primer. By 180, the profile should already be flat; you're just smoothing, not shaping.
Don't skip from 80 to 180. The 120-grit step catches shallow dish-outs and edge transitions that 80 grit missed and that 180 grit can't correct efficiently. Skipping a grit means either spending excessive time at the finer grit or accepting a surface that hasn't been properly verified at the intermediate stage.
Feathering Without Dishing
The featheredge — where filler meets the surrounding panel — is the highest-risk area for dish-outs. If you sand the featheredge more aggressively than the center, you create a ring-shaped depression around the perimeter of the filler that shows through paint as a visible halo.
The fix: extend your sanding strokes well beyond the featheredge, applying the same pressure across the entire stroke. The block sands the filler center, the featheredge, and the surrounding panel surface in one continuous motion. The transition taper develops naturally as the thinner filler edge sands through faster than the thicker center.
When a Dish-Out Is Too Deep to Fix by Sanding
If you've created a significant dish-out (visible under a straight edge, deeper than 1/32 inch), the fix is not more sanding. More sanding removes material from the edges and deepens the dish. Instead:
Clean the dished surface with compressed air. Apply a thin skim coat of filler over the depression. The skim coat should be just thick enough to fill the dish — not a full-depth application. Cure completely, then re-block with 120 grit and guide coat. Verify flatness with a straight edge before advancing to 180.
In a production shop, the skim-coat-and-re-block cycle adds 30 minutes to the job. Compared to the 2–3 hours of repainting a panel that went to booth with a visible dish-out, it's time well spent.
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