Based on certain factors such as desired appearance of the surface, cost, degree of maintenance, etc., the external walls are finished with suitable additional material than mortar. These are various forms of external finishes and some of them discussed below.
1. Sand-faced Finish
Sand-faced finish plaster comprises of two coats. The first coat is carried out in cement mortar of proportion 1 : 4 (i.e., 1 part of cement and 4 parts of clean coarse and angular river sand by volume). The thickness of the first coat is 12 mm and the plaster is watered for at least 7 days. Zigzag lines are made on the first coat so as to give adequate-adherence surface.
The second coat is of 1 : 1 plaster and the thickness is 8 mm. Sand used for the second coat should be of uniform size. When the coat is wet the sponge is worked such that the density of sand grains appearing on the surface is equal and uniform. After completion of the second coat the surface is kept well-wetted at least for 15 days.
2. Pebble-dash Finish
This type of finish is also called as Dry-dash finish. In this type of finish, the finishing coat is made of 12 mm thick. Over this plaster, small pebbles or crushed stones of suitable sizes (from 10 to 20 mm) are thrown and left exposed. The pebbles are sometimes lightly pressed or tapped into the mortar after throwing. It can resist good amount of aesthetic determination.
3. Rough-Cast Finish
This type of finish is also called as Spatter-dash finish. The plaster is of 1 : 3 proportion with one part of cement and three parts of coarse-grained sand by volume. Using a large trowel the mortar is dashed against the surface and the surface is roughly finished by the light movements of a wooden float.
4. Scrapped Finish
In this type of finish, the final coat of mortar is allowed to become stiff for a few hours. Then the surface is scrapped with a steel straight edge, or a board studded with nails or old saw blade in a particular pattern. The finish is a rough finish and is less liable to the cracks.
5. Smooth-Cast Finish
This finish is just similar to rough-cast finish and gives a smooth surface because of use of fine-grained sand. Generally a wooden float is used.
6. Textured Finish
In this type of finish, ornamental patterns or textured surfaces, such as ribbed stucco or fan textures, are made on the final coat of plaster with the help of using suitable tools.
7. Depter Finish
This is another form of rough-cast finish. As in the case of pebble-dash finish a rendering coat of 12 mm thick is prepared. While the coat is wet, pieces of gravel or flint are pressed with hand on the surface. It is possible to have the desired patterns selecting materials of different kind.
8. Machine Applied Finish
Machines are used to throw or spatter the material on the wall in a variety of ways which gives variety of finishes. The machines may be manually operated or mechanically operated. In order to through the material a sort of gun is used.
Any external finish, unless, it is painted should not require any maintenance over a long period of time. Light-coloured finish is required to be maintained only by periodical painting. An external finish is often required to be protected against rain penetration through the walls. Cracks also should be avoided.
Leave a Reply