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Decorating Defects - their cause and cure

Crumbling of Plaster

In some cases, plaster will be found to be in a friable or crumbling condition, due to bad craftsmanship in the first place on the part of the plasterer, or to the action of moisture or alkali.
If the trouble is localised, the affected portion should be cut out and made good with patching plaster, Keene's or other suitable material. In some instances, the whole wall surface will have disintegrated in this way and hacking off and renewing may be necessary, since to attempt to paint or paper over such a ground is to invite trouble from flaking or the paper coming away.
If, however, the defect is no more than slight powdering, the wall may be given a coat of thin oil paint, varnish size (equal parts of turpentine and oak varnish), or petrifying liquid, in order to bed down the loose matter.
The use of size distemper for decorating such walls should be avoided, since it shrinks strongly on drying and the force of contraction may be too strong for the plaster. For a similar reason, paint is to be preferred to a washable distemper on grounds to which it has been necessary to give this kind of preliminary treatment.
In bad cases, the plaster may not only crumble but may actually have broken out in hard swellings, owing to the crystallisation of saline matter in the surface, brought about by the presence of excess moisture.
The matter must be traced to its source and any defective guttering, pipes, or porous walls which are responsible should be carefully and thoroughly rectified, or trouble is bound to recur.