8. PREPARING AND PAINTING A FERROCEMENT HULL

8.1 Preparation
8.2 Filling
8.3 Painting

8.1 Preparation

Great care should be exercised in the initial surface preparation of the ferrocement. The ferrocement will be prepared by etching the surface with solutions which will not harm the ferrocement and/or by wire brushing or hand/mechanical sanding. Whichever method is used to remove latence and salts from the ferrocement surface, a complete wash down with clean water and/or suitable thinners before painting, will need to be carried out.

At least one month should be allowed to elapse after the curing before applying any paint.

8.2 Filling

There are various proprietary brands of suitable fillers available which will use either epoxy or polyester resin combined with an inert material to make up the filler.

When choosing a paint system it is advisable to check which type of filling agent will be compatible with the paint. Also the procedure to be adopted as to when to use the filler, either directly on the hull or in between the coats of paint to be applied.

The degree of filling will depend on the standard of finish required. On fishing boats, if the plastering and the fairness of the hull are up to standard, the filling will be on local areas only.

Any filling applied will need to be sanded down and feathered in to the hull surface and this will require the necessary variety of grade or grit of sandpaper being available for use.

8.3 Painting

The paint system to be used may well be a choice narrowed down by the constraints of price. Generally, there are two systems available:

1. An epoxy system
2. A high build chlorinated polymer system

Both systems adhere very well to the surface of the ferrocement and can be used without any problems. However, the systems should not be mixed.

Painting the hull interior

The inside of the hull will usually require a certain amount of painting, particularly in a fishing boat. Therefore, it is easier to decide how much is to be done before the fitting out work advances too far. Normally the engine room, fish hold and generally through the bilges will be painted, as these areas will be much easier to keep clean from the excess of oil and fish.

As the inside of the fitted out hull is protected from sunlight, two coats of an epoxy primer will be sufficient. In some cases, it may be felt that to paint the whole of the inside of the hull will give a more pleasing finish to the eye.

Painting the hull exterior

Most paint manufacturers have both chlorinated rubber and epoxy systems available.

Whilst carrying out the project in India, paints were obtained from two paint manufacturers both of which supply their paints in many countries, although the paint names indicated may be differently named by the same manufacturer in a different country.

To give an idea of the systems available, a typical example of each will be shown below:

A. Chlorinated rubber paint system

Hull topsides	Spread rate/litre
1. Apply first coat with Interchlor LPL 786 HB light grey primer	5.06 m2
2. Apply second coat with Interchlor LPL 274 HB red primer	5.06 m2
3. Apply third coat with Interchlor LPL 786 HB light grey primer	5.06 m2
4. Apply fourth coat with Interchlor LFB 000 white finish	7.3 m2
5. Apply fifth coat with Interchlor LFB 000 white finish	7.3 m2
Hull bottom (underwater)	Spread rate/litre
1. Apply first coat with Interchlor LPL 786 HB light grey primer	5.06 m2
2. Apply second coat with Interchlor LPL 274 HB red primer	5.06 m2
3. Apply third coat with Interchlor LPL 786 HB light grey primer	5.06 m2
4. Apply fourth and fifth coats with Interspeed BLA 200/BLA 002 antifouling red	6.2 m2

International thinners GTA 007 is used as a brush wash for the above paints.

Overcoat time: 1 - 3: 24 hours or longer
Overcoat time: 4 - 5: 12 hours or longer

B. Epoxy paint system

Hull topsides	Spread rate/litre
1. Apply first coat with Epilux 4 clear varnish	11.0 m2
2. Apply second coat with Epilux 4 white finish	9.1 m2
3. Apply third coat with Epilux 4 white finish	9.1 m2
4. Apply Berger Marine undercoat green	7.8 m2
5. Apply Berger Marine synthetic enamel green	7.8 m2
Hull bottom (underwater)	Spread rate/litre
1. Apply first coat with Epilux 4 clear varnish	11.0 m2
2. Apply second coat with Epilux 4 coal tar epoxy (brown)	45.5 m2
3. Apply third coat with Epilux 4 coal tar epoxy (black)	45.5 m2
4. Apply fourth coat with Protectross Chlororubber HT red antifouling	5.0 m2
5. Apply fifth coat with Protectross Chlororubber HT red antifouling	5.0 m2

Thinners 4/5 is used as a brush wash for the above paints.

The primer coats in the epoxy system should be applied in subsequent coats and an interval of 18-24 hours should be allowed between coats.

The antifouling coats as for system A should be applied just prior to launching the boat.

As can be seen from the epoxy paint specification, the final two coats are conventional marine paints. This is a good requirement because epoxy paints will, after a time, chalk when subjected to ultra violet rays produced by sunlight as well as providing a base for subsequent maintenance painting which may be carried out in a location where epoxy paints are unavailable.

The application of the paints to the outside of the hull in the primer stage can be fitted in to suit the progress of the fitting out and do not require the need for marking off the water line and boot top line.

It will be usual to apply the means of striking the water line prior to applying the hull topside undercoat and top coat. In the case of a fishing boat, very often there is no requirement for a boot top line, but a water line is provided to make the break between the hull topside paint and the antifouling paint applied at a later stage.

Because a ferrocement hull cannot have a batten nailed to it the line needs to be applied using masking tape or similar. The hull must be in a level state both fore and aft, as well as transversely before striking the required line.

Prepare level boards at the stem and transom, with the top of the board set at the desired height in relation to the DWL. Have the boards so that they protrude from the centre line of the hull by the same measurement as the widest part of the hull at DWL. Wedges can be prepared that will provide the swing in the line required.

The line on the transom is levelled and marked, and the masking tape applied.

The lines for each side are made by attaching the masking tape at the correct height amidships and pulling the masking tape out, and keeping off the hull until located at the outside and smallest end of the wedge.

The masking tape is pulled as tight as possible without breaking and is allowed to be worked up the wedge easily. Keep the bottom edge of the tape on the top edge of the wedge until the tape is pulled into the transom or stem depending which end of the boat is being worked on. The same procedure is carried out for the remainder of the lines to be marked. It will be found that an even true curved line is the result. The topside is painted down to the masking tape which is subsequently removed prior to the antifouling paints being applied.

The actual height of the line above DWL will be dictated by the designer's requirements when the boat is in a fully laden condition and therefore will vary from one design to another.

Polyurethane paints might be suggested as an alternative paint to use on top of the epoxy primers. However, despite their good durable qualities, the paint is difficult to apply to a good standard of finish by hand particularly in warm climates. The only means of application is by using spray equipment and a person who can use the equipment to provide the standard of finish desired.

Ferrocement, like many other materials, will have barnacles and grasses attach themselves to the hull. Therefore, it is a requirement to use antifouling paints despite their updating and improvement. Many of those available contain copper salts which leach out of the paint under the action of salt water to produce a poison which keeps the underwater areas clean. Copper is not the best material to apply to a ferrocement hull as it will help set up an electrolytic action. Although many ferrocement boats have been painted with these types of antifouling, if an alternative comes onto the market which is compatible to the other paints being used, they should be preferred.

As a footnote to this section on paints, it will always be desirable to check out carefully what paint systems are available, to suit their application to a ferrocement surface. When approached, the paint manufacturers will always be prepared to provide the information at their disposal.