To sand clear plastic effectively, you typically start with a medium-fine grit sandpaper and progressively move to much finer grits to smooth the surface and prepare it for polishing.
The process involves several steps, using increasingly finer sandpaper grits to remove scratches and haziness.
Step-by-Step Guide to Sanding Clear Plastic
Sanding clear plastic requires a gradual approach, moving from coarser grits to finer ones. This process systematically removes previous sanding marks and surface imperfections, eventually leading to a smooth surface that can be polished back to clarity.
Here are the essential steps:
- Begin with a Medium-Fine Grit: Start with a grit like 320 grit sandpaper. Sand the abraded or damaged surface until any prominent scratches, protrusions, or deep grooves are removed. Apply even pressure and work in a consistent direction.
- Transition to a Finer Grit: Next, switch to a finer grit sandpaper, such as 400 grit. Sand the same area, working in a slightly different direction (often perpendicular) to the previous step. This helps to remove the sanding marks left by the 320 grit paper.
- Refine with an Ultra-Fine Grit: Follow this by sanding with an even finer grit, like 600 grit. Continue sanding until the surface appears uniformly frosted and the marks from the 400 grit paper are gone.
- Continue to Finer Grits (Recommended): For best results, especially on clear plastic intended to be transparent, it's highly recommended to continue sanding with grits even finer than 600. Progress through grits like 800, 1000, 1500, 2000, and potentially even higher (up to 3000 or 5000 grit) if available. Each step reduces the scratch size left by the previous grit.
- Wet Sanding: For steps 4 and beyond (and often starting from 400 or 600 grit), using water (wet sanding) is highly beneficial. Wet sanding reduces friction, prevents plastic dust from clogging the paper, and results in a smoother finish. Keep the surface and sandpaper wet while sanding.
- Clean Between Grits: Thoroughly clean the plastic surface with water and a clean cloth between each grit change. This prevents coarser grit particles from scratching the surface during the next, finer sanding step.
Sandpaper Grit Progression Example
This table illustrates a typical progression, including the initial steps from the reference and common subsequent steps:
| Step | Sandpaper Grit | Purpose | Notes |
|---|---|---|---|
| 1 | 320 Grit | Remove deep scratches/protrusions | Start here |
| 2 | 400 Grit | Refine marks from 320 grit | Progress here |
| 3 | 600 Grit | Refine marks from 400 grit | Progress here |
| 4 | 800 Grit | Further smooth the surface | Start Wet |
| 5 | 1000 Grit | Reduce sanding marks | Wet Sanding |
| 6 | 1500 Grit | Prepare for fine polishing | Wet Sanding |
| 7 | 2000 Grit + | Achieve a very smooth surface for polishing | Wet Sanding |
(Based on steps outlined in Smooth-On FAQ 151 and general plastic restoration techniques)
After completing the sanding process with the finest grit, the plastic surface will likely appear uniformly hazy but smooth. It is then ready for polishing with a plastic polish compound to restore its clarity.
