Sanding gelcoat step by step
How to sand gelcoat properly — choosing grit, wet and dry technique, and preparation for polishing.
Sanding gelcoat is the basic operation when reviving a dull or oxidised hull and when preparing a surface for paint or polish. Gelcoat is the hard, pigmented layer of polyester resin on the outside of the laminate, usually 0.4–0.8 mm (0.02 in–0.03 in) thick — a very thin layer that is easy to sand right through. That is why choosing the grits deliberately and controlling how much material comes off is crucial. Before starting, assess the condition: is the gelcoat merely oxidised, or does it have scratches, cracks or chips that need repairing first?
Work starts with washing and degreasing the hull thoroughly, so that dirt is not rubbed into the surface and does not clog the paper. Light oxidation can often be removed by wet sanding with 800–1200 followed by polishing. Deeper scratches and unevenness are levelled gradually, starting at 400–600 and going through 800 and 1000 up to 1500–2000 before polishing. Never skip several grits at once — deep scratches from coarse paper will still show after polishing.
Wet sanding is recommended for gelcoat, because it limits dust, cools the surface and stops the paper clogging. You use wet-and-dry paper and water with a few drops of detergent, rinsing the slurry off regularly to judge progress. A wet surface also shows the true picture of the scratches — once rinsed and dried you can see straight away whether the previous grit has been fully sanded out. Work evenly, without point pressure, ideally on a block or a soft pad matched to the curve of the hull.
On larger areas a random orbital sander with dust extraction helps, especially at the 320–600 stages when sanding dry. The machine must run smoothly, without tilting, and is guided with light, even pressure. Watch the edges, corners and the area around fittings — that is where gelcoat wears through fastest. Every so often it is worth wiping the surface dry and looking at it at a low angle, to catch spots that are under-sanded or overheated.
Working safely matters even when wet sanding: always wear goggles and gloves, and a P2/P3 dust mask when sanding dry, because polyester dust irritates the airways. Work in a well-ventilated place and protect the surroundings from splashes of slurry. Power tools used wet must be properly protected, ideally through a residual-current device. Regular breaks help keep the quality even over a large area.
Once you reach a uniform, matt surface at a fine grit (1500–2000), the hull is ready for cutting compound and wax, or for a coating. If the gelcoat was very thin and the laminate shows through, it is better to switch to paint than to keep sanding. A well prepared, evenly matted surface is the foundation of a lasting gloss. Patience through the successive grits translates directly into the final mirror finish.
It is worth testing the gelcoat's response on a small, inconspicuous patch and picking the best starting grit. Note which grit you finish each section with, so the whole hull stays consistent. If you plan to machine polish, do not go too fine — a surface that is too smooth after 3000 can make the cutting compound work longer. A well thought-out grit plan saves material, time and the gelcoat layer itself.
Material prices — products and options
Indicative prices in EUR (incl. VAT), as of July 2026. Products widely available in Europe; prices depend on the shop, the pack size and consumption. The links lead to example shops that ship across the EU. Dollar amounts are converted at 1 EUR = 1.1622 USD (ECB, 7 September 2026) and rounded — treat them as a rough guide, not a price in a US shop. Imperial values in brackets are conversions of the metric figure.
Abrasives (discs and paper)
- Mirka — Abranet 150 mm (pack of 50)
dust-free abrasive mesh, grits P80–P600 for gelcoat and composites€30–55 (≈$35–64) / pack - 3M / Mirka — wet-and-dry paper P400–P2000
sheets for wet sanding, a set of finishing grits€1–3 (≈$1–3) / sheet - Mirka — Abranet Grip P120/P150 (disc)
hook-and-loop discs for random orbital sanders (intermediate sanding)€0.80–2 (≈$0.93–2) / pc
Polishing and finishing compounds
- Farecla — G3 cutting compound (250 g (9 oz) / 1 kg (2.2 lb))
single-stage compound for removing dullness and sanding marks€8–30 (≈$9–35) - 3M — Perfect-it cutting / polishing compound
finishing compound for high gloss after G3€20–40 (≈$23–46) - Menzerna — polishing compound (cut / finish)
professional German compound for gelcoat and paint€15–35 (≈$17–41)
Waxes and protection
- Collinite — gelcoat wax (885 / 925)
durable protective wax for use after polishing€18–35 (≈$21–41) - Yachticon — hull wax / polish
protective wax for gelcoat with a UV filter€12–25 (≈$14–29)
Degreasing and personal protection
- Cleaner / degreaser before polishing
removing dust, salt and grease before work€6–15 (≈$7–17) - P2/P3 dust mask + goggles
respiratory protection when sanding gelcoat€10–30 (≈$12–35) - Nitrile gloves (pack of 100)
hand protection when using compounds and solvents€6–12 (≈$7–14)