Ferrocement is a special type of reinforced concrete where reinforcement bars and a dense mesh placed between them are covered with high-quality mortar. This creates a material with high tensile strength and flexibility.

Ferrocement is a relatively inexpensive boatbuilding material, with the advantages of being non-combustible, durable, and easy to repair. However, it is heavy compared to other boatbuilding materials, and achieving a high-quality finish through fairing and painting requires specialized expertise. A two-component painting system is recommended for ferrocement.

Tips for painting ferrocement:

• Ensure that new ferrocement has fully cured.
• Roughen the ferrocement surface by hand with silicon carbide using water as a lubricant, or wet-sand it with 120-grit wet/dry sandpaper.
• Alternatively, the hull can be roughened by sandblasting or wet-sandblasting to create a slightly rough, clean surface.
• All reinforcing wires and similar elements exposed during this process must be cut below the surface of the substrate.
• The cavities formed by cutting should then be filled.
• Acid-wash the surface with a 5% by weight nitric acid or phosphoric acid solution.
• Allow the acid to act for 2–4 minutes, then rinse with fresh water.
• Check that the pH of the surface is between 6.5 and 8.0 and that a sharp knife leaves a clean mark on the surface.
• Allow the surface to dry naturally.

Two-component system products:

Below the waterline

• Hempel Light Primer
• Hempel Antifouling paints

Article photo: Jouko Heikola