Spraying versus Brushing.

It will be convenient now to consider the length of time involved in spraying, as compared with that involved when painters' brushes are used.

In dealing with this question, it should be pointed out that while some little gain is apparent in the actual time occupied in handling the article, which is mostly done on turn-tables when spraying, yet no note is taken here of the difference in handling, but only the time occupied in covering the article with paint, japan, etc.

We will take, by way of example, a modern gas fire. Very few of these are now brushed. It is the consensus of opinion that a gas fire takes 10 minutes to brush.

To spray one, with a superior finish, takes 30 to 45 seconds, and even where some difficulty is experienced in handling, or where it is the practice to have the firebricks in place beforehand, so necessitating the use of a mask, in no case is a greater time than 1½ to 2 minutes taken. A cycle lamp, small size, takes fully 2 minutes to brush properly. To spray the same lamp takes 10 seconds. A gas meter, 5 or 10 light size, takes 7 minutes to brush. To spray one takes 1½ minutes, allowing for the time occupied in fixing and removing the somewhat elaborate mask employed for covering the indicator glass, badges, name-plate, etc.

A motor headlight takes nearly 20 minutes to brush properly, whereas to spray one takes but 1½ minutes at the outside.

To brush a cycle frame takes 10 minutes or so (brushing is still done for coloured work).

To spray either in japan or colours takes 1 to 1½ minutes, and when it is considered that a heavier coat can be applied than is the case when brushing or dipping, it will be admitted that such a result compares favourably even with dipping.

A 2-seater motor body takes from 25 to 45 minutes to brush properly.

To spray the same body takes only 6 to 8 minutes, and when it is noted that a fraction of the rubbing down is necessary in the case of the sprayed result, as against the brushed body, it will be granted that an enormous gain is to be effected.

Where two or more colours are employed, it is difficult to make comparisons as readily, but, generally speaking, it is the practice to employ two instruments per operator where the colours are applied one immediately after the other, as is the case with many electrical parts, and in this case a gain of 4 or 6 to 1 is shown over brushed work.

In some cases it has been found an advantage to spray one coat and to brush the other, especially where some difficulty is experienced in masking, and, in such cases, the only way to arrive at the most satisfactory method is by actual test.

In other cases, such as bronzing, with a celluloid medium, it is absolutely impracticable to apply these bronzes, save with the spray, unless the old method of varnishing and afterwards dusting on the bronze is adopted; but, of course, against spraying, such an obsolete method as the latter has absolutely no chance when speed is considered.

Iron piano frame manufacturers have almost universally adopted the system of spraying bronze on the frames. Where the old-fashioned method is still in use, it is usually because the quantity of frames to be dealt with is hardly large enough to justify the outlay required in the purchase of a plant.

Another advantage should be mentioned. The special celluloid japans now largely used for application by means of compressed air obviate the necessity of a considerable amount of rubbing down and papering, etc., which cannot be dispensed with when the liquid is applied by means of a brush.

For the purpose of comparison, it may be said that these japans may be sprayed upon such articles as buttons, medallions, electrical and bedstead fittings, and also on wood brush-handles and furniture, large and small, with a gain of 5 to 1 over brushing.

Objections Sometimes Urged Against Spraying.

Having explained the advantages of the spraying system, we may now consider the objections which are occasionally raised against it.

One of the arguments most frequently used is that the effect thereby obtained must be less durable than is the case of the brushed effect.

Why such a theory should be advanced is a little obscure, for, theoretically, it is possible to apply, with a properly fitted plant, a far more even coat than is the case when brushing, and seeing that such paint is applied with the idea of protecting the article against rust, or corrosion, or of improving the appearance, the argument is for rather than against spraying.

However, to come to the practical side, the evidence is all in favour of spraying, for it has been proved by many exhaustive tests by independent persons, that, with the same material treated in the same manner, i.e., either air dried or stoved after spraying or brushing, there is no difference in the durability of the japan or paint, and that the sprayed result has this advantage, that some little gain in time is effected in the period occupied in drying or stoving of the paint.

Another objection is sometimes raised to the application of paint by means of the spray to rough and uneven surfaces. The argument here is that it is impossible to make the paint adhere to the surface, save with a good stiff brush.

Such arguments ignore the pressure at which the paint is applied, which is usually between 30 and 45 lbs. per square inch, and are mainly based on unfortunate experiences with early types of whitewashing machines, which have already been pointed out to be entirely unsuited to painting problems.

Again here, it may be positively stated that in no case has it been found that a less durable finish is obtained with the spray. As a fact, an advantage is to be recorded in that on rough surfaces the gain in time is enormous, for such surfaces may be spray-painted as rapidly as the smoothest surface obtainable, whereas the labour of brushing such rough surfaces is very considerable.

Still another objection which may be mentioned is the slightly mottled appearance which the sprayed surface sometimes shows when finished—if such can be objected to seriously.

This objection may be met by the statement that such a mottled effect is only apparent when the paint has not been specially prepared for spraying, and is mainly due to the fact that mediums used dry rather too rapidly and do not allow the paint (which is, of course, applied in minute spots) to flow out.

The remedy is naturally to re-model the paint should the mottled appearance be objected to, but most certainly such an effect, if not pronounced, is not any worse than brush marks, which are always noticeable unless rubbing down has been done.

In passing, it may be stated that most of the large paint and varnish manufacturers have experimental plants for producing spraying materials, and they are naturally well able to answer any queries which may be likely to arise and which may not be adequately dealt with here.

Many firms who consider the question of adopting a spraying plant seem to have the idea that while the principle is admirable for many trades, yet it cannot be successfully employed in their particular case, and one frequently finds the manufacturer of small goods wondering why his neighbour opposite, who makes, we will say, motor bodies, does not install a plant, although, of course, in his own case the question is impossible. Most probably, at the same time the said neighbour has precisely similar thoughts, save that he considers the only proper use for a plant is in small work.

Occasionally one hears the opinion advanced that primers or fillers cannot be applied with a sprayer, or, if so applied, it is at a risk that they will either crack or peel off afterwards.

This objection may just as readily be advanced in the case of brushing. If trouble of this kind occurs, it is not due to the method of spraying, or brushing, so much as to the way in which the paint has been used. This statement sounds paradoxical, yet it will be understood by practical men. For instance, it is obvious that motor bodies, par exemple, must be dealt with by the expert coach-painter as far as the methods, number of coats, etc., to be employed are concerned, even though the work may be carried out by unskilled labour, and naturally whether brushed or sprayed, motor bodies cannot be well done by novices.

To summarise, it may be confidently stated that whatever difficulties there may be in the application of paints, enamels, varnishes, lacquers, etc., by means of brushes in the ordinary way, these are certainly never accentuated but are in most cases considerably lessened by the use of an adequate spraying plant.

Spraying and Dipping Compared.

In considering those articles which may be dealt with either by dipping or spraying, the manufacturer has first to take into account the number of coats necessary.

If, for instance, to produce the correct finish on a cycle frame, when dipping, needs three coats, and assuming that the same effect may be obtained in two when spraying (and this is frequently the case), then spraying must be considered to rank favourably with dipping, and if allowance be made for the time taken to drain, and the room occupied with an elaborate dipping plant, then again spraying scores, for a cycle frame can be sprayed in 1 to 1½ minutes, or, say, 40 to 50 frames per hour, which is very little, if any, less than can be comfortably dealt with by dipping, and, of course, no time is lost in draining.

If, on the other hand, gas is so cheap as to be of little consequence whether two or three stovings are necessary, and if some of the work can be done with two coats, then the saving effected when spraying would not be sufficient to warrant the outlay necessary for a modern compressed air plant, unless a fair proportion of coloured work, not easily dipped, was required to be dealt with. In this latter case, a spraying plant ought to receive very serious consideration.

To take another case. Some gas fires may be dipped, but, owing to their weight and to the fact that they are seldom entirely free from grit or dust, they are not a satisfactory type for dipping, and we venture to state that all the leading gas engineers have dropped the question of dipping such work in favour of spraying, although in some cases, for gas cookers, the accessories, such as burners, bars, racks etc., are dipped.

Such accessories are as readily sprayed, but as only one coat is applied, naturally no saving is shown over dipping.

Other goods sprayed or dipped are steel implements, hoes, spades, shovels, axes, picks, etc., and in some cases it is an advantage to dip where the same colour, black, red, etc., is needed, say, half-way up the spade or hoe, but otherwise spraying should be adopted; and, of course, in many cases where two colours are employed it is out of the question to dip, the only alternative being to spray or brush—spray for preference on account of the enormous saving of time over brushing.

Where very small articles are dealt with in bulk and can be so handled that trays may be used, then these are undoubtedly better dipped; but if various colours are needed it is better to still use the trays, but to spray them, as the speed is approximately the same as when dipping.

A tray full of camera parts is sprayed almost instantaneously and with a far better finish than if dipped.

To sum up the various arguments advanced on this subject, we may come to the following conclusion.

As already intimated, the saving effected by painting by immersion or by spraying as compared with brushing is very large indeed, provided that a properly equipped plant is employed, and the paint or enamel is exactly fitted for the purpose. The question must often arise as to whether dipping or spraying is the best and cheapest to employ. The answer is that everything will depend upon the nature of the article that is to be painted. Speaking generally, painting by immersion possesses many advantages, because the actual work of applying the paint is done in a few minutes and every part of the article is covered with paint at one time. In reaping machinery, iron treads of staircases and many other parts of the kind in which there are a large number of small parts or depressions, paint dipping cannot be improved upon; on the other hand, spraying possesses distinct advantages in dealing with many classes of goods which are of such a shape or character that if the paint were applied by dipping some accumulation in parts would inevitably occur.

A decision on the subject can only be arrived at after a very careful study in comparison of the two methods. It will frequently be found that, on the whole, the most economical plan to pursue is to dip the first and subsequent coats, excepting the last, and to spray this on, particularly when it consists of varnish or a viscous liquid. It is in this particular that one can draw a wide distinction between the two methods. In dipping, the paint must not be very thick, and, as previously stated, in designing a paint for the purpose the greatest effort is made to produce one which gives a happy medium between excessive thickness and the reverse, too thin a coat. Just as soon as the peculiarities of the article to be painted necessitate the use of all thick paint or enamel it must be considered that dipping is not suitable, but that spraying is. The latter may be employed successfully with any liquid up to the thickness of tar.