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Decorating Defects - their cause and cure

Mould and Fungus.

The appearance of mould and fungoid growths on painted surfaces is by no means rare, yet it is strange how uninformed the average decorator seems to be as to the cause and cure of this defect. When it develops, many men do not connect its presence with the paint film and attempt to obliterate it with another coat of paint-an action which only serves to make matters worse, for it has been definitely established that these growths actually do feed on the paint film itself.
The condition most favourable to the formation of mould is a warm, damp atmosphere, particularly when rotting or decayed vegetable matter is to be found in the neighbourhood. Absence of light or ventilation also encourages its growth. It is believed that the surface of paint offers a lodgment for spores floating in the air or deposited by moisture, and that under the conditions just mentioned, the spores sprout, forming a downy mass, pale or white at first but which later assumes a colour that varies according to the nature of the fungus.
Mould growths find sustenance on organic matter such as paper, paste, size, distemper, or oil, and are consequently liable to attack most forms of applied decoration. They appear in the form of spots, usually in clusters, or patches of various colours, according to the species of the fungus. The type most commonly encountered is the black mould (Aspergillus niger) though the ordinary greenish-blue variety (Penecillium glaucum) is often found. In greenhouses and conservatories, where the atmospheric conditions generally favour their development, a reddish-purple species (Phoma pigmentivora) occasionally develops.
On paintwork, mould growths are more likely to attack films which owing to their nature, incline to be soft, than those which dry to a hard and glossy surface, which offers rather less lodgment for them. For a similar reason, quick-drying coatings present less risk of this form of trouble than those which take longer to harden and remain soft and tacky over an ex­tended period.
Whether or not the basic pigment from which the paint is made exerts any influence in the formation of these growths, is not easy to determine. They thrive freely on white-lead coatings but there. is some reason for supposing that zinc oxide, while not actually fungicidal, is fungistatic, i.e. it does not actually destroy the spores but does not encourage their germination.
The eradication of mould growths on applied decoration is complicated by the fact that on occasion, not only the decoration itself, but the plaster behind it, may be infected. In bad cases, it may even be necessary to hack off the plaster and renew it with fresh material, but as a rule it will be sufficient to sterilise the surface; if this is not done thoroughly, the new decorations may be attacked.
Treatment.-All infected paintwork, distemper, wallpaper, or other coatings should be stripped to the bare plaster and burnt, in order to pre­vent the spores from reaching other areas. The plaster should then be given an antiseptic wash. A very large number of materials have been recommended for this purpose but the most reliable are probably those advocated by the Building Research Station(War-Time Building Bulletin No.111) as follows:
tI. A 1 per cent. solution of sodium pentachlorphenate (I lb. to 10 gallons of water). This material was obtainable under the name of" Santo­brite," from the Monsanto Chemicals, Ltd., Ruabon.
2. A 1 per cent. solution of the sodium salt of salicyl anilide. This was obtainable under the name of " Shirlan N.A." from any sales office of Imperial Chemical Industries, Ltd.
3. As an alternative to either of the above a solution of 6 oz. zinc silico­fluoride to a gallon of water can be used. Before applying the sterilising solution, the plaster should be well brushed down and thoroughly dry. The wash should be brushed on liberally and, if circumstances permit, the surface should be left untreated for two or three weeks and examined periodically during this time for any signs of new growths; if the latter appear, they should be removed and a fresh application of the wash should be made.
Redecoration can then proceed in the ordinary way but it is a wise pre­caution, if paint or distemper is to be used, to obtain from a supplier some to which a sterilising agent has been added in the course of manufacture. It is not advisable for the painter himself to add a fungicide to his material as this may affect its durability in other respects.
The surest and most durable remedy against mould is to improve the conditions which give rise to its formation. The source of the dampness, which is sure to be present, should be traced and steps taken to rectify this defect, while the provision of adequate light and ventilation is another essential measure.
Breweries and places in which processes of fermentation are habitually carried out are peculiarly susceptible to the formation of mould, and allowances should be made for this fact when buildings of this kind are being painted, special paints being essential.