Painting Plastered Surfaces

Lesson 27 : Painting, Varnishing, Distempering And White-Washing

Painting Plastered Surfaces

Newly plastered surface may contain considerable moisture. Hence painting should be resorted to only after 3 to 6 months of plastering. Calcareous surfaces to lime and cement plastered surfaces are highly alkaline because lime is liberated during hydration of cement. Due to this, oil based paints and distempers are liable to alkali attack. Hence it is essential to apply alkali resistant primer. Absorption of liquid from a paint by a porous surface is known as suction. High suction may make the paint difficult to apply and leave the coating in an underbound condition. Uneven suction may cause lack of uniformity in the finished appearance. The variation in suction characteristic sof the surfaces to be painted require corresponding variation of the priming coat, or, in some cases, the use of glue size, petrifying liquid or sealers according to the type of paint to be used. Surfaces which show local variations in suction, as for example, between individual bricks or on patches produced on plastered surfaces by local over-trowelling Or by efflorescence, should be treated by the application of a suitable primer.

If the suction is so high or variable that normal painting procedure is likely to give a good finish, one of the following pretreatments should be applied over the whole surface as a primer, according to the type of paint to be used.

Type of Paint

Pretreatment

(a) Size bound distemper

  1. One coat application
  2. Two-coat application

A coat of clearcole
A coat of size alone will be sufficient

(b) Dry distemper

A coat of the same distemper thinned with water or petrifying liquid
Or
A coat of ‘ sharp colour’ or primer sealer with the addition of finely ground pumice.

(c) Oil paint

A coat of thin primer or prime-sealer, preferably in consulation with the manufactures of the paint.

(d) Emulsion Paint

A coat of the sme paint thinned with water or sealers recommended by the manufacturer.

(e) Cement paint and lime wash

Wet the surface before applying paint.


In the case of new lime plaster, the following points are note-worthy:

  1. If possible, lime plaster should be left unpainted for the first few months so as to allow the plaster to carbonate, harden and dry thoroughly. If the plaster has any tendency to craze or crack owing to shrinkage on drying, the movements should be allowed to occur before the surface is painted, so as to enable provision of suitable preparatory treatment. Heating the rooms, if accompanied by good ventilation, will assist drying, but should be cautiously adopted. Too rapid drying may damage the plaster by causing undue shrinkage and separation of the plaster coats.

  2. If there is any objection to leaving the plaster base, a temporary decoration of soft distemper (non-washable distemper) may be applied. This may be removed easily at a later date and replaced by a more permanent decoration. Other types of paint suitable for early application are cement paints, silicate paints and washable distemper depending upon the final decoration in view.

  3. If the background of the plaster is one likely to contain large amounts of water, for example, new brick work, concrete or building blocks, no attempt should be made to apply oil paint (specially gloss finishes) until there is every reason to believe that the walls are thoroughly dry.

  4. If the background is of a dry type, for example, wood or metal lath, oil paints may be applied with the safety after a few weeks drying, and oil-bound distempers even earlier.
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Last modified: Monday, 2 July 2012, 9:59 AM