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Plastic & resin · 1 min read

Sanding GRP: boats, motorhomes, body parts

Keying gelcoat, levelling repairs, refining before paint: the sequence from P80 to P600 – and why the dust must stay out of your lungs.

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Short answer: the grit sequence

  1. P80→
  2. P120→
  3. P180→
  4. P240→
  5. P320→
  6. P400→
  7. P600
Random orbital sander on the door of a black car

Levelling the repair

Shape cured laminate or filler with P80 to P120, feathering the edges out wide so the transition will not show later. Do not sand into sound laminate – as soon as fibres become visible, you have gone too deep.

Gelcoat and paint preparation

Before painting, sand intact gelcoat matt with P240 to P320. For antifouling, P120 to P180 is often enough. If you only want to refresh the gelcoat, wet sand up to P600 and polish afterwards.

Light pressure: GRP heats up under the machine, the resin smears and the disc clogs.

Protection from the dust

GRP dust contains fine glass fibres that irritate skin and airways. Dust extraction on the machine, at least an FFP2 mask, long sleeves and gloves. Wet sanding binds the dust wherever it is possible.

FAQ

Which grit should I use to key antifouling?

Usually P120 to P180, until the surface is matt and sound. Antifouling dust is toxic: wet sand or use extraction, and wear a mask and gloves.

The whole sequence at once

7 grits, 1 × smallest pack each: PRO NET 150 (10 pcs) P80 · P120 · P180 · P240 · P320 · P400, PRO CUT 150 (10 pcs) P600.

Or as a set: Finish set for high gloss (P1000–P2000) for €59.90 →

incl. VAT, plus shipping

All steps: Plastic →Adjust the sequence in the calculator →

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