Clean, professional hull preparation is the most important step for a long-lasting F2 coating. Only if the substrate is dry, clean and sound can F2 EcoHull bond optimally and deliver its full performance. 

In this article, you’ll learn how to prepare your hull step by step so you can start applying the F2 coating without any “legacy” layers trapped underneath. 

Quick overview: The key steps

  1. Check hull condition (moisture, old coatings, damage).
  2. Sand old antifouling layers consistently back to the underlying primer (our clear recommendation).
  3. Apply barrier coat/primer where needed (especially on new or bare hulls).
  4. Sand the hull evenly (P80–180), tidy up edges and details.
  5. Clean thoroughly and degrease with F2 Degreasing Solution – without using solvents.
  6. Make sure everything is dry, dust-free and ready for the F2 coating.

1. Planning & prerequisites

Depending on boat size, condition of the old coatings and your working speed, you should plan around 2–3 working days for hull preparation (not including the actual F2 coating). Thorough preparation saves headaches later – poor substrates under F2 are very difficult to fix afterwards. 

1.1 Checklist – what you should have ready

  • Random orbital sander with P80–180 abrasive discs
  • Sanding block / hand sanding paper for edges and tight areas
  • F2 Degreasing Solution
  • Clean buckets and soft sponges/cloths
  • Masking materials (foil, tape) for waterline, fittings, etc.
  • Protective equipment: dust mask, safety glasses, gloves, ear protection
  • Optional: hull moisture meter

1.2 Environmental conditions

Even during preparation, you should pay attention to suitable conditions – temperature and humidity become especially critical once you start coating. 

ParameterRecommendation
Suitable substratesGRP/gelcoat, aluminium, steel and wood.
Hull condition The hull must be dry. If in doubt, check with a moisture meter. 
Work area Work in a low-dust environment, vacuum or sweep sanding dust regularly. Avoid other sanding work nearby while you are applying the later F2 coatings. 

2. Assessing the hull condition

Before you pick up the sander, you should inspect the hull thoroughly. This initial assessment determines how aggressively you need to remove the old layers. 

2.1 Visual inspection

  • Blisters, flaking or cracks in the old antifouling?
  • Soft, smeary or heavily chalking areas?
  • Zones with past repairs or osmotic blister treatment?
  • Areas coated with silicone, sealants or specialist systems?

2.2 Checking moisture

F2 coatings must not be applied to damp hulls. If you’re unsure, a moisture meter (especially on GRP) helps to identify critical areas. Elevated moisture readings or suspected osmosis need to be addressed first – F2 must not be used as a “sealing layer” over existing problems. 

3. Old antifouling layers: our clear recommendation

Important: For F2, we generally recommend sanding old antifouling layers consistently back to the underlying primer. This prevents legacy coatings from being trapped under the F2 system and minimizes the risk of future delamination. 

Traditional, soft antifoulings are not designed to act as a permanent base for a modern fouling-release system. Under an F2 layer, they can continue to move, swell, chalk or detach – and in the worst case compromise the entire coating. 

3.1 Why “back to the primer”?

  • Soft or poorly cross-linked old coatings always remain a risk.
  • Trapped layers can later cause blisters, cracks or large-scale delamination.
  • On the primer/gelcoat/metal surface you can choose a clearly defined, stable coating system.
  • You start with a “clean system” without unknown third-party products underneath F2.

3.2 How to remove old layers

  1. Mechanical removal: Depending on layer thickness, start with a coarse grit (e.g. P60–P80) and gradually move finer (P80–P120).
  2. Work with control: The goal is to sand back to the sound primer – not to grind aggressively into the laminate/metal. Stop regularly and check which layer you are currently on.
  3. Silicone & specialist systems: Silicone-based coatings must be completely removed. Even small silicone residues can severely disrupt F2 adhesion.
  4. Fairing & smoothing: Clean up uneven transitions, scratches and sanding marks with a suitable grit (e.g. P120–P180).

Only in exceptional cases – such as after a recent, professionally executed hull refit with a clearly documented system – can you consider whether a full strip is really necessary. Our standard recommendation, however, remains: remove old antifoulings thoroughly. 

4. Bare hulls & barrier coats

On new hulls or where you have sanded back to a completely bare surface (GRP, metal, wood), the substrate should be coated with a suitable barrier/primer system before applying F2. 

  • GRP/gelcoat: Solvent-free epoxy barrier coat (e.g. Hempel High Protect II) to protect against moisture ingress and osmosis.
  • Aluminium/steel: Suitable anti-corrosion primer according to yard or manufacturer recommendation.
  • Wood: Depending on the system, epoxy sealer or an appropriate primer so that the F2 layers sit on an even, stable base.

If you use a solvent-based primer, this must fully cure first (often at least 7 days at around 20 °C). Only then should it be sanded and degreased with F2 Degreasing Solution before building up the F2 system. 

5. Sanding – the base for adhesion & finish

After removing the old antifouling layers (and building up a barrier coat if needed), the hull is sanded to create an even, slightly matt surface. 

  1. Grit range: Generally, P80–180 works well. Coarse grits (P80) for old, stubborn coatings, finer grits (P120–P180) for the final sanding passes.
  2. Work evenly: Use the random orbital sander in overlapping passes to achieve a consistent sanding pattern.
  3. Edges & details: Sand edges, curves and tight areas by hand so there are no sharp transitions or missed spots later.
  4. Remove dust: Vacuum or sweep dust regularly so you can see remaining irregularities and old layers clearly.

6. Cleaning & degreasing – the final step before F2

After sanding, the hull must be completely free from dust, grease, oil and wax residues. Only then can the F2 coating bond reliably. 

6.1 Initial cleaning

  • Vacuum or sweep off sanding dust thoroughly.
  • Rinse the hull with fresh water to remove salt and loose dirt.
  • Allow everything to dry completely.

6.2 Degreasing with F2 Degreasing Solution

  1. Mixing: Dilute F2 Degreasing Solution at a ratio of 1:10 with fresh water.
  2. Application: Apply the solution to the surface with a clean sponge or cloth.
  3. Wiping technique: Wipe in one direction only – do not scrub back and forth, to avoid redistributing dirt and grease.
  4. Repeat: Repeat the process as needed until the surface appears clean with no visible streaks.
  5. Rinse & dry: Rinse with clean water and allow the surface to dry completely.

Important: Do not use solvents (e.g. acetone, thinners) for final cleaning. They can leave residues that impair the adhesion of the F2 coating. 

7. Final check: Is your hull ready for F2?

Before you start applying the actual F2 coating, run through the following checklist: 

  • All old antifouling layers have been removed back to a sound primer – no soft or unknown coatings remain under F2.
  • The hull is dry; any osmotic issues have been treated properly, not simply “painted over”.
  • Any barrier coats/primers are fully cured and sanded.
  • The surface is evenly matt and smoothly sanded.
  • The hull has been cleaned thoroughly and degreased with F2 Degreasing Solution.
  • No visible dust, grease or silicone residues.

If you can tick all of these boxes, your hull is optimally prepared for the F2 coating – with no legacy layers and a clearly defined substrate. The next step is the actual system build-up with F2 EcoPrimer (if required), F2 EcoHull Adhesive Coat and F2 EcoHull Top Coat.