colors and the after-action of caustic lime upon them.
There are certain requirements in the way of workmanship as well which must be fulfilled. Authorities differ on many points of execution in this medium, but there is apparently a unanimity of opinion in regard to the necessity for having a proper sort of surface upon which to apply sgraffito. Most important of all is that the surface shall be dry and healthy, free from saline properties. If the walls are damp, external applications of silicate washes, or a coating of stucco, will be found effective.
Given an ordinary brick or stone wall, there should first be applied a priming coat of common plaster, to % inches in thickness. A i :3 mix is considered good for this priming coat, which should be applied several days before the ones used for decorative purposes are needed. It must be thoroughly tapped and sounded to insure its being firm, and it is essential to provide a good key for the second coat.
The second coat may consist of one part Portland cement to one part sifted silver sand and one part distemper. Portland cement used for this purpose must not be fresh from the kilns, as in such new material shrinkage is likely to occur, which will cause cracks. It is well to use a little lime, also, in this coat, to retard the setting, which would otherwise occur in a few hours, and would not permit time for scratching. Plaster applied for this purpose without lime shows a tendency to develop hair cracks, as does plaster of Paris, which also sets very rapidly. There are workers in this medium, however, who have achieved very successful results in the use of cement alone. This color coat may be as thin as % to % inches and must be very perfectly applied.
The third, and last, coat should be applied as soon as the second is ready to receive it. As soon as it is floated on and troweled over the work of transferring the drawing and scratching on the decoration must be undertaken and carried out as rapidly as possible, before the plaster has time to set.
A silicate binder in the top and second coats is of great value in keeping the plaster soft—sometimes for as long as eight days. This gives an opportunity for more careful workmanship in execution than would ordinarily be possible. In Italy lime was used to the exclusion of cement. This lime, however, was seasoned underground for a year after slaking, with the result that plaster made from it would remain soft for several days, and when it did set was as hard as rock. It has been said that a plaster made from a natural unity of materials, not forced into a connection, will grow in time into a solid mineral wall. The top coat should be merely a “skim,” and can be applied with a large brush.
PALAZZO PICCOLOMINI DEL MONTE, PIENZA, ITALY
There are certain requirements in the way of workmanship as well which must be fulfilled. Authorities differ on many points of execution in this medium, but there is apparently a unanimity of opinion in regard to the necessity for having a proper sort of surface upon which to apply sgraffito. Most important of all is that the surface shall be dry and healthy, free from saline properties. If the walls are damp, external applications of silicate washes, or a coating of stucco, will be found effective.
Given an ordinary brick or stone wall, there should first be applied a priming coat of common plaster, to % inches in thickness. A i :3 mix is considered good for this priming coat, which should be applied several days before the ones used for decorative purposes are needed. It must be thoroughly tapped and sounded to insure its being firm, and it is essential to provide a good key for the second coat.
The second coat may consist of one part Portland cement to one part sifted silver sand and one part distemper. Portland cement used for this purpose must not be fresh from the kilns, as in such new material shrinkage is likely to occur, which will cause cracks. It is well to use a little lime, also, in this coat, to retard the setting, which would otherwise occur in a few hours, and would not permit time for scratching. Plaster applied for this purpose without lime shows a tendency to develop hair cracks, as does plaster of Paris, which also sets very rapidly. There are workers in this medium, however, who have achieved very successful results in the use of cement alone. This color coat may be as thin as % to % inches and must be very perfectly applied.
The third, and last, coat should be applied as soon as the second is ready to receive it. As soon as it is floated on and troweled over the work of transferring the drawing and scratching on the decoration must be undertaken and carried out as rapidly as possible, before the plaster has time to set.
A silicate binder in the top and second coats is of great value in keeping the plaster soft—sometimes for as long as eight days. This gives an opportunity for more careful workmanship in execution than would ordinarily be possible. In Italy lime was used to the exclusion of cement. This lime, however, was seasoned underground for a year after slaking, with the result that plaster made from it would remain soft for several days, and when it did set was as hard as rock. It has been said that a plaster made from a natural unity of materials, not forced into a connection, will grow in time into a solid mineral wall. The top coat should be merely a “skim,” and can be applied with a large brush.
PALAZZO PICCOLOMINI DEL MONTE, PIENZA, ITALY