POINTING AND PLASTERING
The exposed surface of walls are to be provided with pointing or plastering.The process of pointing is adopted for stone masonry or brick masonry while plastering is carried out for exposed surfaces of sailings, walls, columns, etc.
OBJECTS OF POINTING AND PLASTERING
- To improve the appearance of the structure as a whole and to give smooth surface.
- To protect the exposed surfaces from the effects of atmospheric action.
- To rectify the defective workmanship or to conceal inferior materials.
The term pointing used to denote finishing of mortar joints of either stone masonry or brick masonry.The joints are raked out to a depth of about 20 mm and then, these spaces are filled up by suitable mortar in the desired shape .
It is desirable to avoid pointing as far as possible. This is due to the fact that pointing involves raking out of joints which are constructed with good mortar and filling the joints with mortar which, in many cases, is not sufficiently watered.For this reason, the pointing work of new structure should follow the masonry work in progress.The joints are thus raked out when the mortar has not set.
Mortar for pointing: The pointing is generally adopted for the finishing of exposed external walls of a structure. It is cheap in the first coat, but it requires frequent replacement. The pointing may be carried out either in lime or in cement mortar. The lime mortar consist of equal volumes of lime and sand. These two materials are carefully mound in a mortar mill. The sand to be used for preparing lime mortar should be clean, fine and free from any organic impurities.
The cement mortar consists of equal volume of cement and sand. The cement should comply with standard requirements and sand should be clean, fine and free from organic impurities. The materials are thoroughly mixed in dry condition before water is added to them. The mixing of materials is done on watertight platform and mortar of one cement bag only is prepared at a time and this quantity of mortar is consumed within 30 minutes after adding water.
Method of pointing
Method of Pointing: The pointing is carried out as follows:
- The mortar of masonry joints to be covered by pointing is raker out at least to a depth of 20 mm.
- The dust from the masonry joints is removed by the brushes.
- The surface is then washed within clean water and it is kept wet for a few hours.
- The mortar is then carefully placed in desired shapes in these prep are joints.
- The mortar is placed by a small towel and it is slightly pressed to bring into close contact with the old interior mortar of the joint.
- The finished surface is well-watered for a period of at least 3 days, It lime mortar is used and 10 days, if cement mortar is used.
- Beaded pointing
- Flush pointing
- Recessed pointing
- Rubbed or Keyed or grooved pointing
- Struck pointing
- Tuck pointing
The term plastering is used to describe the thin plastic covering that is applied on the surfaces of walls and ceilings. The plastering removes the unevenness of the surfaces and sometimes the plastering is used to develop decorative effects.
Requirements of good plasters: Following are the qualities of the plastering materials so as to turn out good plaster.
- It should adhere to the background and should remain adhered during all variations of the climatic changes.
- It should be cheap and economical.
- It should be hard and durable
- It should be possible to apply it during all weather conditions.
- It should effectively check the entry or presentation of moisture from the surface.
- It should possess good workability.
- Lime mortar
- Cement mortar
- Water-proof mortar
In order to improve the binding properties of mortar, a kind of fragrant gum-gugal is added to the lime mortar. The quantity of gugal is about 16N per m3 of mortar.The gugal with enough quantity of fresh water before it is with the lime mortar.The quantity of hump is about 10 N per m3 of mortar.The mortar thus prepared is kept for two days before use and it is turned ones in a day to make the mortar of uniform nature.
Cement mortar: The cement mortar consist of one part of cement to four parts of clean, coarse and angular river sand by volume.The materials are thoroughly mixed in dry condition before water is added to them.The mixing of materials is done on a watertight platform and mortar of one cement bag only its prepared at a time and this quantity of mortar is consumed within 30 minutes after adding water.
Water-proof mortar: This mortar is water proof and is prepared by mixing one part of cement, two parts of sand and pulverised alum at at the rate of 120 N per m3 of sand.In the water to be used, 0.75 N of soft soap is dissolved per one litre of water and this soap water is the added to the dry mix.