For best results, wallpaper should be applied to a clean, properly sized plaster surface. If the plaster is new, it should be given sufficient time to set and dry. All cracks should be opened and filled with plaster. If the plaster is old, and is already papered, or calcimined, or painted, it should be treated, before sizing, as explained below. Old paper must be removed to ensure satisfactory results. The paste coming in contact with the lime of the walls has a preservative effect. Placing one layer of paper over another cancels out this effect and forms a breeding place for germs.

Moreover, it often results in a "bumpy" job, due to the old paper blistering or curling at the corners when it is moistened by the paste. This is especially undesirable in bathrooms. Even if you don't have a steam sauna or a steam shower, the hot moisture from a regular shower can absolutely destroy a poorly done wallpaper job. To remove the old paper, wet the entire wall with warm water, applying it with a calcimine brush. Allow enough time for the water to soak the paper. Try a spot on the wall with a broad scraper. If the paper does not come off easily, do not dig into it.

The wall will be damaged, necessitating much plastering. Soak the paper once more and try again to remove it. Do this until the paper comes off easily. If there are several layers of paper, remove the top ones that have become soft, wet the wall again, and remove the remainder. Varnished papers prevent water from penetrating through. In order to remove the paper, it is necessary in this case to cut the varnish with No. 1 1/2sand- paper. Scratch the surface enough to allow the water to soak through.

The addition of two handfuls of washing soda to half a pail of warm water will help in the penetration and softening of the paper. This is especially easy to access if you are working in a bathroom that has a bathtub with hot water gushing from its bathtub faucets. Do not add washing soda to the water if the woodwork is not to be painted, as it will be marred by the soda solution. From this point, the procedure is the same as for unvarnished papers.

Wash the walls with clear warm water to remove glue and bits of paper that have remained on the surface. If the walls are calcimined, the calcimine should be removed before papering. Wet a section of the wall about 5' square with warm water. With a sponge, wash off the softened calcimine. Do not wet too large a section at a time, as calcimine absorbs water readily and sets quickly. If the walls are painted, paper can be applied over the paint by rubbing the paint thoroughly with No. 1 1/2 sandpaper and by washing well with weak washing soda solution, or with hot soapy water to remove oil and grease.

Before sizing, all cracks in the plaster walls should be opened and filled with plaster. After repairing and cleaning, the walls are ready for a coat of glue size. Where paper has been removed and the surface cleaned, a weak size will be sufficient. Newly plastered walls should also be given a weak size coat. Painted walls will not permit absorption of the glue in the size, with the result that the size will remain on the surface, and the paper will not adhere firmly. Penetration can be obtained by the addition of vinegar (acetic acid) to the size. A small amount of acetic acid in the size will cause it to cut through and penetrate the surface, carrying the size with it. If you are working in a bathroom, most of the bathroom fixtures may be rendered inaccessible, so use the shower beforehand. 

Size is made as follows: purchase 1/2 lb. of flake glue from your paint dealer. Place this in a pail with enough cold water to cover the glue. Allow it to soak for at least 2 hours, after which the water is poured off. Place the pail containing the glue over a slow fire and boil it until it is free from lumps, stirring continuously to prevent it from burning on the bottom. Pour this mixture into a little less than half a pail of hot water and stir well. For a weak size, more water is added.

The strength of the size can be tested by placing a little of it between the thumb and forefinger. Wait a few minutes until it begins to set and feel the "tack" (stickiness) by pressing the two fingers together. A weak size, such as is required for a lightweight paper, will have little tack. Heavy papers require a stronger size. Half a pint of molasses to half a pail of size, added while the size is hot, increases the stickiness and makes the size elastic. This is desirable as it prevents the size from forming a "skin" which may be pulled from the wall by the paper.