Plastering as Building Finishes and the Defects

Plastering is enhancing the aesthetic value and hygiene condition in a building. Plaster finished surface also gives insulation to thermal, fire and sound. The surface finish can be obtained as smooth, semi-rough or rough as per the desired aesthetic appearance using ganging trowel, Regi foam and sponge. Cement sand mortar is used as the plaster mix.

Important aspects to be considered when plastering

  • Plastering work should be levelled, plumbed up and the joints should be at right angle at the corners or edges.

  • It must cover the non-verticality and non-horizontality of walls and columns which are resulting from poor workmanship and non-standard bricks.
  • Generally, the plaster thickness should not exceed 15 mm. Else the mortar bulk might tend to fall due to its self-weight and thus the cracks can be initiated in later stages.
  • The mortar mix proportion of cement: sand = 1:5 is generally used for the wall plastering.

Procedure for plastering

It is must to ensure all mechanical and electrical work which associated with the plaster surface should be completed before commencing plastering. Any holes left in the wall or honeycomb effect should be filled with construction grout. The surface should be cleaned well to remove the dusts, loose particles and efflorescence in bricks and then it should be wetted thoroughly.

1:5 cement: sand mortar should be mixed thoroughly and applied on the prepared surface from top to bottom and levelled by using the straight edge and plumb bob. After plastering, curing should be done for entire plastered surface. The curing should be continued for at least 7 days to protect the plastered surface from initiation of thermal cracks.

What is Febmix?

Febmix (Original Vinsol Resin) is an air entraining plasticizer mixed with mortar instead of lime to obtain desired workability without adding more water to the mortar (it makes the application of mortar easier and quicker). Thus, the shrinkage cracking or crazing arising when the applied mortar is being set out, can be prevented with the usage of this admixture or with any similar admixture. And, it reduces the efflorescence in surface and mortar mix being plastic for longer time.

Defects in Plastering

The defects in the plasterwork can be caused due to several reasons. The bricks, mortar and concrete have some amounts of voids themselves.  Moisture movement that is causing by drying process of moisture inside the bricks, mortar and concrete during the initial setting out or due to absorption of moisture from environment and expand is main reason for the crack development. Quality of bricks used, workmanship of brickwork or plastering work, quality of mortar mix used, water containing salt used for mortar mixture and dry condition of the plaster surface are some other reasons for the defects in the plastering.

Proper proportioning and mixing of contents and good workmanship (avoid excess troweling) is important to prevent the surface from cracking.

Crazing and Map cracking, De bonding, Lack of hardness, Grinning, Expansion, Popping and Blistering are the possible defects in the plaster surface.

  • Crazing is caused because of over troweling the mortar with high cement content. This can be covered easily with the reasonable quality paint with appropriate filler.

  • De bonding is due to different shrinkage rate through the plaster thickness and can be noticed if a hollow sound is heard when tapping the surface. The main reason for this type defect is the excessive thick plaster layers. Cleaning the surface well to remove dusts and oil, damp the wall properly and applying the cement slurry coat on the surface before plastering can be minimized the de bonding.
  • Lack of hardness can be observed only by scratching the surface and this is causing due to insufficient cement content, using the sand with excess dust and adding some more water after first mixing (re tempering).
  • Grinning is due to excess troweling.

  • In the case of drying shrinkage cracks, the crack should be dug along the crack as a ‘V’ notch up to 10 mm or up to crack depth with 10 mm wide. This v notch should be made to ensure a bonding with the infill material (construction grout). Then the surface should be cleaned well to obtain dust free surface and made it wet. The construction grout can be mixed with water and applied on the cleaned ‘v’ notch.