For one or more purposes, the exterior masonry walls are finished with suitable materials. These include protection from rain-poisoning, decorative appearance, protection from atmospheric exposures, and increased durability. The process of finishing an external wall is known by “rendering” and the result is called “Rendered Finish”.
The performance of an exterior plastering in wellington is dependent on many factors, such as cost, maintenance and desired performance. There are many types of exterior finishes. e.g. Sand faced, roughcast, smoothcast etc. The exterior walls of the buildings have been finished with appropriate materials. The specifications and colours of the buildings are determined by many factors, including:
- Decorative appearance desired
- Maintenance degree
- Protection against rain penetration
- Conditions that can affect durability
- Background material for the surface to be finished
- The year in which the finish must be applied
Plaster’s durability is dependent in large part on its adhesion to the background. To achieve a uniform surface and reduce plaster consumption, all projections that extend beyond 13 mm of the wall’s surface are removed.
The Preparation for an External Plaster is shown below.
Before plastering work
Before you start external plaster, make sure that the masonry work has been completed in every respect
- Plan ahead for scaffolding where plaster will be applied
- The external gaps in the masonry and the joints between the beam and wall must be filled. This was impossible to do from the outside without scaffolding.
- All wooden pieces, papers, rope, and kathya (rope), must be removed. Remove all other unwelcome material from the R.C.C. and masonry surfaces
- Before plastering, let the surfaces dry for at least a day.
- Before plastering, make sure you check the top of the parapet walls
- All windows and door frames should be checked. For plumb, line, and level. Before plastering can begin, rectify any defects
- All elevational features should be checked according to the architectural drawing
- Before you start the exterior plaster, mark level dots
- Clean the R.C.C surface with a wire brush if it is affected by algae or efflorescence.
- Line Dori should be drawn from the top slab to the bottom. It should include all corners of walls and windows. A line of elevational features. Grill and any straight line within that section.
- For sufficient strength, the process should be started at least two days before plastering.
- Limit the plaster’s thickness to a minimum.
- You should clean all joints and surfaces with a wire brush.
- To fix chicken mesh to any joints of masonry or R.C.C, drill a hole in the beam, column, and wall with a drill machine.
- You can choose between 12 mm chicken mesh or 24 gauges of external plaster.
- Use a cutter to cut the chicken mesh at a minimum of 20 cm to 23cm in width.
- Fix the chicken mesh at joint R.C.C. and masonry walls by installing plumbing nails on R.C.C. member and wire nails onto masonry member.
- Half of the chicken mesh width will be on masonry walls and the other half on R.C.C members
- The chicken mesh should be sufficiently tight in all directions, horizontal and vertical.
- To avoid chicken mesh buckling or loosening, spacing of nails should not exceed 9 inches (23 cm).
- The surveying instrument/centre plum bobs can be used to align and fix level pegs on exterior wall surfaces.
- For all corners of walls, windows, elevational features, lines, R.C.C grill lines, and other straight lines, fix Dori (string), from the top slab to the bottom level.
- After completing the levelling, the plaster- or unevenly-textured projections of the wall will be removed.
- For surfaces with mortar thicknesses exceeding 20mm, first coat mortar filling (1.4 Cement and sand) will be applied up to 12 mm.
- The plaster for external walls will have a rough finish.
After plaster work
It is recommended that plasterwork be left to cure for at least 7 days after it has been completed.
If a high-value project is being undertaken, resourceful contractors will use the “H” frame and steel tabular scaffolding. These are self-supporting and don’t require support from the wall.
For small projects, double scaffolding should not be used. When only one scaffolding is being used, the contractor will erect one bamboo raw and then take down support for external walls that are to be plastered. To support the wooden balls on each floor, contractors usually drill holes in the walls. These holes are left behind after the first coat, and they will be filled with second coat when scaffolding is removed. This creates a joint in plaster that is not skillfully done.
It will cause a patch that will look and feel bad, but also allow water to enter. This is where moisture can enter and cause damp walls. It is not necessary to mention the difficulty of curing scattered holes. External plaster should always be treated with double scaffolding.
The selection of a particular plaster is dependent on many factors, including availability of material, location of plastering surface and weather conditions, economics, desired decorative appearance, etc.