Minimising defects in plastering work

Defects in plastering work can be minimised by following the below mentioned techniques.

1. The brick and plastering work should be carried out by skilled masons in the best workmanship manner.
2. Bond of brick work should be properly maintained.
3. Efflorescence is removed by rubbing brushes on the damaged surface. A solution of one part of hydrochloric acid or sulphuric acid and five parts of clean water is prepared and it is applied with the help of brushes on the affected area. The surface is then washed with clean water. It should, however be remembered that it is desirable to prevent efflorescence than to cure it. Building material should be selected of superior quality and suitable methods of construction should be employed.
4. Water should not be used to wash the surface so as to remove efflorescence. In that case, soluble salts will be partly carried inside the surface and efflorescence will appear again. For this purpose, the deposit is brushed off from the surface as it appears and the surface is kept under observation for a further period of few days. After curing, if efflorescence appears again it is removed with a dry brush and the process is repeated till all the soluble salts are removed under the conditions of normal drying. It is advisable to postpone painting till efflorescence ceases.
5. Bricks of superior nature should only be used for brick work.
6. Water free from salts should be used for brick work and plastering work.
7. The surface to be plastered should be well watered so that it may not absorb water from the plaster.
8. Excessive trowelling should be avoided.
9. Damp-proof courses should be provided at convenient places in the building.
10. The overall construction should be such that penetration of moisture is prevented.
11. Fresh plastered surfaces should be protected from the superfluous quantity of water such as rain and excessive heat such as sun.
12. The concrete surface which is generally plain and smooth should be hacked to form kay when the concrete is green i.e. the moment the shutters are removed. However, this point is generally neglected and the work of plastering is taken up in a hurry on the surfaces a it is or with slight hacking. This will lead to peeling at later stage.
13. If the surface is not properly hacked, there are two alternatives to make the surface rough:

§  Clean the surface by water so as to keep surface wet & an acid treatment with 1 part of muriatic acid diluted in 10 to 20 parts of water applied on the surface. More than one coat may be necessary. After this treatment the wall should be washed through with water to remove all traces of acid.

§  Sometimes, some surfaces cannot be roughened by acid also and the better method would be a spatter dash key.

WHAT IS SPATTER DASH?

                 Spatter dash

It simply means a rich mixture of Portland cement and coarse sand thrown onto a background by a trowel, scoop, or other appliance so as to form a thin, coarse-textured of continuous coating. As a preliminary treatment, before rendering, it assists bonding of the undercoat to the background, improves resistance to rain penetration, and evens out the suction of variable backgrounds.

In this method a mixture of coarse sand (8mm and below) mixed to cement in the ratio of 1:1.5 and water equal to 0.5 part by total volume is dashed on the walling in an un-even manner. Where sharp sand is difficult to obtain, crushed hard stone (with fine particles eliminated) can also be used.

The water content will vary with the type of aggregate. The dry materials must be mixed thoroughly & then water gradually added. The mixture must be continually stirred during use.

The spatter dash need not cover every piece of surfaces and it is an advantage if parts of surface are not covered. The main object is to form a large number of small humps of mortar so as to make surface as irregular as possible. The thickness of spatter dash may be limited to 10 mm. On allowing 2 to 3 days with good curing; further work can be taken up. Of all the methods to provide a key, the spatter dash method is to be preferred in practically all cases.

14.  In brickwork, raking of joints on the finished side should be done as soon as the day’s brickwork is over to provide effective keys for holding the plaster.