Causes of plastering defects and proper remedies
Several plasterwork problems occur due to improper use of materials or the techniques applied in plastering operations.
Given below, some common plastering defects :-
Some cracks perceptible in the plaster may originate from cracking of the wall. These are because of differential movement of the foundations, moisture development or drying shrinkage of masonry units, or thermal movement of the roof. This type of crack is found in straight vertical or horizontal lines, or in stepped diagonal lines. The crack width will frequently change with the seasons.
To get rid of cracks, structural revisions are necessary to transform cracks into movement joints. Visible joints are concealed with cover strips which are set on one side of the joint or sealed with elastomeric sealants.
Plaster done with extremely thick layers, is likely to debond from the wall when the outside skin compresses at a different rate than the plaster touching the wall. It happens because of insufficient substrate formation.
Areas greater than the size of a plate should be detached and substituted with the following:
- Clean dusty or oily wall surfaces in detail.
- There should be exact moisture content in all the walls.
- Apply a cement slurry or spatter dash coat prior to plastering.
- Use bonding liquids and follow the methods suggested by the manufacturer.
Lack of hardness
The plaster should contain good strength but the plaster becomes soft because of the following reasons:
- Inadequate cement.
- Application of sand with unnecessary quantities of dust (above 15% by mass passing the 0,075mm sieve).
- Application of a mix with weak water-retention properties.
- The inclusion of excessive water for a long period once the first mixing is made (a practice called as re-tempering).
It is recommended to use a slightly weaker plaster as it is prone to less cracking or debonding, as compared to strong plastering.
Normally, extreme moisture loss in initial phase occurs for the following reasons:
- Evaporation, if plastering is done in sun and wind.
- Suction into the walls, when the masonry units are not moistened.
- Application of bad grade sand that does not contain fine material (below 5% by mass passing the 0,075mm sieve).
- Non-existence of building lime or a masonry cement when the sand does not contain fine material.
Grinning is applicable if the mortar joints are seen evidently through the plaster. It happens because of the variation in suction among the masonry units and the mortar, as well as by eliminating mortar joints.
Application of an undercoat or a spatterdash coat prior to plastering can stop grinning.
It involves swelling, softening, layer cracking and spalling of the plaster. It happens due to the existence of proprietary gypsum-based products in the mix. Under moist conditions, the sulphate from the gypsum create reaction with the Portland cement paste and builds up compounds having bigger volume which break up the plaster.
The only solution for disruption caused by gypsum in the mix is to take out and substitute the plaster.
Pop-outs stand for conical fragments that suddenly begin of the plaster surface. These are produced by contaminant particles in the mix, which, when react with the moisture in the mix, spread out and lead to cavities in the plaster.
As soon as the reason of the pop-out is eliminated, the hole can be filled with a proprietary filler and painted over.
The elimination of important areas of plaster work from the background.
The scaling away of patches of plaster surface owing to defiency or loss of adhesion with the previous coat.
A deposit of soluble salts on the surface of the plaster or background.