The interior surfaces of such buildings, owing to the influence of moisture and the emanations from plants, often develop most unsightly stains, which are actually produced by a very minute fungoid growth.
The best way to kill these stains and to prevent their recurrence on the new paint is to treat them with a solution of corrosive sublimate. Great care is called for in the use of this substance. It can be purchased in the form of small tablets, two of which should be dissolved in half a teacupful of hot water. By means of a piece of stick with a pad of cloth or sponge on its end, the affected parts should be touched with the solution. When dry, the parts so treated should be given a coat of the knotting varnish previously mentioned.
Another preventative of this trouble is to add a few drops of carbolic acid to the first coat of paint.
A third alternative treatment is to wash down the whole of the interior woodwork before painting with coal-tar naphtha.
No painting should be done during damp or foggy weather. What is to be sought for is a condition of absolute dryness in the work under treatment.
A Final Caution
A large part of the secret of successful painting consists in not putting one coat of paint on the top of another that is not thoroughly dry and hard. Forty-eight hours is not too long an interval between each coat.