In the course of his work the painter will sometimes be called upon to paint or repaint certain articles or structures, the treatment of which involves special considerations. Surfaces of this kind include those of baths, radiators, blackboards, and greenhouses, and notes on the best procedure to adopt in each case conclude this post.
Although the stove-enamelled bath is now the general rule, a number of baths finished with air-drying paints still survive in some of the older houses and the decorator may be called upon to renovate them from time to time.
It is well to emphasise at the outset that no matter how good the quality of the paint and enamel used or how carefully and skilfully it is applied, no air-drying finish can be expected to compare in durability with one of the stoved variety and can, in fact, have only a limited life. This should be made clear to clients who are sometimes inclined to grumble when the finish of a bath shows signs of wear and tear within a few months of its having been renewed by the house painter.
As a general rule, it will be found that the finish on the sides of the bath is in fairly good condition and that flaking has occurred only on the bottom or at the end where water from the taps has dripped upon it. It may not be necessary, therefore, to strip the whole of the old finish though better results will always be obtained if this is done, as it should be if there is any doubt as to the adhesion. If it is not, the edges of any bare patches should be carefully feathered, and the remainder of the paintwork well rubbed down. If the metal shows any indication of rust, as will usually be the case, all traces must be removed by means of emery paper, steel wool, or similar abrasive. Stringent precautions should be taken to ensure that, before painting, the whole of the surface is clean and free from grease.
As soon as possible after the rust has been removed, all bare metal should be primed with a good rust-inhibitive paint, and there is probably nothing better than red lead for this purpose. This should be allowed several days to harden. If any surfacing is needed, two or more coats of filler, preferably on a slate-powder basis, as used by coach-painters, should be given, allowing plenty of time between coats. When this is hard, the surface should be well flatted and an undercoat based on zinc oxide applied. If costs permit, after this has hardened and been flatted, a second coat should be given, in which event the first should contain rather more oil than the second. Flat down once more when this is dry and finally apply a coat of bath enamel. Allow this to dry for at least two days and then, after plugging the overflow, fill the bath to the brim with cold water and allow it to remain in this condition for a further forty-eight hours. The bath should not be used until the finish is perfectly dry and if the client can be induced for a few weeks, when filling the bath, to run a little cold water into it first and then to add the hot water, the finish is likely to wear better and last longer.
From the above, it will be seen that the process of repainting a bath is a protracted one, but in view of the conditions to which the finish will be subjected in service, ample intervals for the various coats to dry and harden are essential, if the work is to last for any reasonable length of time. The longer the surface is allowed to stand after painting, before the bath is used, the better.
Some painters do not agree with the practice of filling the bath with cold water after the finishing coat of enamel has been applied, on the ground that this interferes with the process of oxidation. It should not, in fact, be done until partial oxidation has taken place – hence the idea of waiting until forty-eight hours or so after the enamel has been put on. The object is to harden off the finish. The hardening action depends on the formation of hard soaps which are the result of reaction of the zinc-oxide pigment and linseed oil, and it is generally agreed that it occurs more rapidly when oxygen is excluded.