Figure 7.2. A paint brush is an excellent tool for stripe coating

Coating should be brushed on to all areas which for any reason cannot be properly spray coated. Surfaces not accessible to brushes should be painted by other suitable means to ensure a uniform paint film of adequate thickness.

Brushes shall be of a style and quality that permit proper application of the paint. If available, it is recommended to always use a round brush. Round (or oval brushes) generally are considered most suitable for rivets, bolts, irregular surfaces, and rough or pitted steel.

The main disadvantage with brush application is that the coats will be thinner and less even than obtainable by spraying. Also the method is time consuming. In practice therefore we see that the brush is mainly used for:

• Touching up areas which are difficult to reach

• Stripe coating of edges, corners, weld seams, around notches, etc.

Ideally, a paint brush could be used for the first coat of paint and the subsequent coats could be applied using a paint roller or, alternatively, by means of airless spray.

7.1.2. Roller application

Application by roller is a commonly used method. Rolling is primarily suitable for large flat areas such as the exterior of a tank or the flat side of a ship. Experiments and practical experience have shown that application of the first coat with a roller is not to be recommended. This is particularly true on surfaces where the pre-treatment has not been ideal or where moisture or other impurities having collected on the surface. Areas generally not suitable to be coated with a roller are: Complicated structures, porous or uneven surfaces, corners, sharp edges, along areas with many bolt heads or rivet heads

The reason for this is that the physical forces involved are quite different from those of brushing and spraying. The roller lays the coating on the surface as the roller moves ahead. Since the roller moves easily, there is little slipping, sliding or scrubbing action to improve wetting of the surface. The result is poor contact between the uneven surface and the paint. Air pockets and void spaces will remain underneath a paint film applied on porous or uneven surfaces. (Remember the physical action when using a brush). Also, by using a roller, a lot of air is pushed into the paint. During the drying/curing process all the air will try to get out from the paint film. Some of it will succeed, depending on temperature and ventilation, some will create pinholes and some will remain within the paint film or on the substrate surface. The pinholes will create pin point rust very soon, entrapped air will increase the water uptake and the air left on the metal surface will reduce the adhesion.

The major rule is therefore, never to apply the first coat of paint by roller.

A paint roller may be used with good results for subsequent coats.

Paint glove.

This is used for stripe coating of edges, around cut-outs and on thin pipes and railings. The method leaves only a thin film on the substrate. Also the glove often leaves behind fur. This method should only be used when other tools are unsuitable.