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Decorating Defects - their cause and cure
Efflorescence
This defect, which shows itself in the formation, on both interior and exterior wall surfaces, of a white powdery substance of a crystalline nature, has been considered at some length in the section on the priming of plaster and cement, and need be dealt with only very briefly here.
The trouble is due to salts from the backing, brickwork, or mortar, being dissolved by moisture and carried forward in solution either to the outer or inner face of the wall where, when the moisture evaporates, they crystallise out.
Inside a building they may pass through a paint, distemper, or wallpaper treatment and form on the surface, or the crystallisation may take place behind the paint or distemper coating, disrupting the latter and causing flaking.
It should be emphasised that there is no certain cure for this defect and no attempt should be made either to seal up the surface to prevent the formation of the powder, or to neutralise the salts with any chemical. If efflorescence takes place on the surface of the decoration, it can be removed by scraping or stiff brushing without much difficulty and without much damage to the finish. Removal should always be done by a dry method. If water is used it will dissolve the salts, but they will crystallise out again when the moisture evaporates.
The powder will renew itself and continue to form so long as there are sufficient salts in the wall structure and sufficient moisture to dissolve them and bring them forward. Although the defect is most commonly found in new buildings, due to the drying out of the large amounts of water used in bricklaying, plastering, and cement work, it may also occur in old buildings if moisture finds its way into the wall and the necessary salts are present within the latter. In the latter case, if the trouble originates from the brickwork having become porous so that rain seeps through, a cure can be effected by waterproofing the outer face of the wall, thereby preventing the further entry of water to dissolve the salts.
Apart from this treatment, and the removal of the crystals by dry scraping or brushing, there is nothing the decorator can do to remedy this condition.