Painting by Immersion and by Compressed Air: A Practical Handbook

by Arthur Seymour Jennings

Spraying Ships' Hulls.

It is the opinion of the author that the painting of ships' hulls may be done by means of spraying with a great saving of time. Although there are no available statistics, it is probable that many thousands of acres of surface on ships' bottoms are re-painted every year. A careful enquiry has shown that some experiments have been made in this direction, but that they have always been of a somewhat perfunctory character. The very large surface gives an opportunity for the use of the spray which is almost unequalled in its possibilities. There are, however, certain difficulties in connection with this work, which have doubtless had much to do with the fact that it has not, thus far, been adopted to any considerable extent.

The first of these is that the composition applied is not ordinary paint, but one which is mixed with arsenic, mercury and other poisonous compounds, which are added in order to destroy animal and vegetable life and prevent the adhesion of barnacles and other marine growth. So necessary is this that compositions are made suitable for different waters through which the vessel must pass, and it is well known that those vessels which sail by regular routes need much less frequent painting than a tramp steamer which may sail in any direction and through any sea. The reason is, that in the first case the composition is specially made to withstand the growth of life in well-defined waters, while in the case of tramp steamers it must be more or less of a general nature.

The point, however, which has now to be dealt with, is that the addition of arsenic, etc., added to the paint, causes it sometimes to settle out, but it is suggested that this could be easily overcome by an agitating apparatus in the paint pot. As explained elsewhere, such an apparatus is frequently used in ordinary painting, when the composition of the paint demands it.

The second and more serious objection to spraying ships' hulls is that the work must be done in the open, and that the wind will carry away a portion of the paint and prevent it reaching the surface required. It is suggested, however, this might perhaps be overcome by adopting a form of enclosed cabinet, which would screen the operator from the wind. This could be rendered portable by being mounted on a platform with wheels, and a system of elevators, and be adopted with a little ingenuity to reach the higher parts of the vessel. In any case, the subject is one which is well worth the attention of those interested in spraying, owing to the immense field it opens up.

In this connection attention may be directed to the illustrations which appear on pages 252 to 254 of the apparatus used for spraying by the Pennsylvania Railroad for painting their freight cars. This apparatus may be adapted, with suitable modifications, for ship painting also.

Slate Enamelling.

The usual procedure followed in connection with enamelling on slate for mantel-pieces, stall-board, signs and other work of the kind, is to get the slate slabs quite smooth and level by means of a slate planing machine. A coat of "black varnish" or enamel is then sprayed on, and is stoved at 160° to 170° F. Careful rubbing down with powdered pumice and water is next done, when the work receives a second coat of enamel. It is again stoved and then rubbed down by hand to a finish with rottenstone and oil. Sometimes, the slate receives three coats, the finish being left with a high gloss, but more frequently the semi-gloss obtained by rubbing with rottenstone is preferred. It is unsafe to stove slate at higher than 260° F., as it is likely to break when cooling.

Formerly, a great deal of this class of work was done in imitation of various marbles, mostly worked on a black ground, but "marbling" is now done but rarely. The method is to employ a shallow tank of water upon which are placed colours in imitation of the veins of the marble to be imitated. This colour is of a special kind, made to float, and is manipulated on the surface. The slab of slate, which has received one coat, is then dipped gently in the water, when the colour adheres to it. A coat of stoving varnish completes the operation.

Many slate enamellers still employ the old method of applying the enamel by means of brushes, but it is only a question of time before compressed air will be used almost exclusively, for the reason so frequently urged in this work, viz., that the spray eliminates brush marks and, therefore, greatly reduces the work of rubbing down.