Ferro-cement boat hulls are not the most popular in the marine industry. They present the boat owner with unique maintenance problems. The cement composite is poured over an iron frame of rebar and hardware cloth. Consequently the boat's hull surface is rough and grainy, similar to a concrete porch or sidewalk. Whether on a boat hull or on the garage floor, painting cement requires a few unique preparation steps.
Remove any existing coating from the boat hull. Various methods will effectively remove the existing coatings, including power removal with sandblasting equipment or mechanical removal with a wire brush.
Examine the boat hull for any cracks, dents or similar surface damage.
Remove any loose or broken pieces of cement material from the damaged area using the putty knife. Before repainting the boat, remove all loose cement and debris from the damaged area.
Grind a V-shaped groove into the surface of the hull around any damaged areas. By preparing the surface, the new cement patching compound will adhere to the existing substrate.
Mix the approved cement patching compound according to manufacturer's instructions. Stir into the patching compound the quick-setting liquid additive.
Roll a small amount of patching compound into a golf ball size lump. Work this material into the damaged area with your hands. Ensure that no air bubbles or voids exist in the patching material and that it adheres firmly to the boat hull.
Allow the patches to dry before proceeding with the painting process.
Mix muriatic acid with water to create a four parts water to one part acid solution in the garden sprayer. Soak the hull with fresh water. Spray the muriatic acid solution on the cement hull. Spray a 2-by-8-foot area at a time, thoroughly wetting the surface of the concrete.
Scrub the surface with the stiff bristle brush or broom. This process will etch the cement and prepare the hull for the paint coatings. Etch the boat in a well-ventilated area or out-of-doors.
Rinse the hull with pure water and allow to thoroughly dry. The surface is now ready to be painted
Apply the paint according to manufacturer's instructions. A minimum of two coats of paint are applied with adequate time allowed for each coat to dry thoroughly. Most marine-based paints are solvent or epoxy-based products. These paints require longer dry times. The painting process should not be hurried.
Apply solvent-based paints with airless spray painting equipment. An airless sprayer is the most effective way to apply solvent-based paints on the cement surface. Once the paint is sprayed onto the boat hull, use the paintbrush to brush the paint into the cement surface. This process, called "back brushing," ensures a good bond between the cement surface and the paint.
Apply epoxy-based paints with paint brushes and rollers.Do not run epoxy-based paint through airless spray painting equipment. As the epoxy cures, it could render the airless equipment useless.