The next operation is to prepare the surfaces to receive the paper. If they are bare plaster never before treated preparation is simple. It consists in dusting down the walls and applying a coat of thin size, which is made by melting J lb. of concentrated size powder in, say, a gallon of boiling water by stirring, and allowing the solution to cool before use.
The object of this sizing is not to stop all suction, but to reduce and equalize it.
If the surface has been previously distempered with ordinary size distemper, this must be thoroughly washed off, otherwise the paper will not adhere for long. After washing off the distemper, a coat of thin size must be applied.