GRP decks with a moulded anti-slip structure are durable, lightweight and robust. However, as they get on in years, they are difficult to keep clean. As with smooth surfaces, the gelcoat weathers and dirt settles in the recesses. The contrast is particularly striking when the hull and superstructure have a freshly polished shine, while the deck remains dull and dirty.
Normal brushes and deck cleaners won't get you very far - the dirt remains in the valleys. Classic polishing doesn't work either: sponges or lambskin only reach the peaks of the structure; the dirt remains in the valleys. With coarse structures, such as those found on older X-Yachts, the polishing materials are literally ground away. The wear is enormous and the cleaning effect is zero.
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After various experiments with different materials, a tip from the polish manufacturer brought the breakthrough: polish and a hard brush - not applied by hand, however, but with a brush attachment on the cordless screwdriver. With the rotating brush, the polish also grinds into recesses and removes stubborn dirt.
The result is not a high gloss, which would not be desirable for an anti-slip deck, but a much cleaner, smoother surface. However, the amount of work involved should not be underestimated. Depending on the depth of the structure and the degree of soiling, you can only manage 1.5 to 2 square metres with one battery charge. The machine pulls hard and is a real pain in the arse. Wooden parts should also be masked off, as the brush spreads polish and loosened dirt generously in the surrounding area.
No shine, but desired cleaning effect
The choice of polish is crucial. It should be water-based and without waxes so that it is easier to clean. Products such as Mirka Polarshine 45, Sealine S1 or Menzerna Green Line are suitable. These so-called one-step polishes are coarse enough to sand off dirt, and on smooth GRP they would polish from matt to high gloss. On textured decks, you won't achieve a gloss, but you will achieve exactly the desired cleaning effect.
The method is simple: work on small areas, apply a generous amount of polish and work first at a low speed and then at a slightly higher speed. An important trick: Change the direction of rotation of the cordless screwdriver from time to time. This ensures that you get all the edges of the recesses and the brush remains aggressive.
After polishing, the surface must be thoroughly cleaned with a microfibre cloth and water. You only realise how much material was actually involved when you wipe it off. After drying, wipe again to remove any dust residue. Then comes the polymer sealant: it prevents new dirt from quickly settling again. If you are working on a deck with little structure, you should be careful: The sealer can make the surface very slippery.
The working method step by step
1. rough cleaning
Discolouration can be easily removed with a gelcoat cleaner. This cleaning method does not reach the deep-lying dirt.
2. preparation
Mask off the wooden parts, then apply the sanding polish generously. Select a medium grain size.
3. distribute
Spread the polish at a slow speed and work in at a higher speed. The direction of rotation ...
4. incorporation
... so that all flanks are sanded. Water spray mist keeps the work area moist.
5. post-treatment
Thoroughly remove the polish residue and wipe with water, then seal the surface.
6. control
A direct comparison clearly shows how effective the cleaning of the anti-slip structure is.
Short and sweet: checklist to tick off
- Rough cleaning: Remove discolouration
- Preparation: mask off, apply sanding polish
- Distribute: Spread polish
- Incorporate: Change direction of rotation, keep moist with water spray mist
- Follow-up treatment: Remove polish residue, wipe with water, seal
- Control: Check the result of the cleaning
Hauke Schmidt
Test & Technology editor
