Plaster work refers to grey finish/rendering of brick walls or ceilings using a thin layer of sand and cement. Earlier mud-lime mixture was also used for required wall finishes however in modern construction it is completely replaced now with cement sand plaster. Plaster material is first prepared as dry matter in required content ratios and later water is added in it to form a paste type material that can be applied on any surface easily. Plaster mortar can be prepared in different ratios such as 1:3, 1:4, 1:5 etch which we have already described in our earlier article under the heading of Mortar & concrete ratios. Plastering is a technical task that is carried out by experienced masons using certain tools such as:
Plastering is the critical stage of house construction process since it has to be the final look after completing grey structure. All irregularities or defects if any in brick work of walls must be covered or minimised during plaster. There are various technical points that should be kept in mind before and after plastering a wall to get a smooth and flawless finish. Before plastering wall must not be dry and should be cured with clean water to maximum limit until the bricks stop absorbing water. However this process should be carried out at least 8-10 hours before plastering the walls. If this curing is carried out right before plaster, mortar will not settle on walls or if it settles, cracks will appear when it dries.
If wall to be plastered is more than normal height then scaffolding should be arranged and mason should be provided with a task of completing whole wall in one go to avoid joints. After curing next step of plaster process is the application of thin cement liquid spray on the walls which in local language is known as “Neeru”. If the surface to be plastered is extraordinary smooth such as in case of ceilings, then it should be made rough first before applying neeru. Once neeru is applied, next step is to mark the plumb line level in vertical direction which will make sure plastering being done is in vertical level and any defects in brickwork are rectified.
Once plumb level are marked and verified, straight edge levels are checked for vertical marked levels too to verify horizontal level. Next step is the application of mortar on walls using trowel (کرنڈی/کانڈی) with such a force that mortar sticks on walls or surface which is being plastered. A big patch of wall is applied with mortar which is then straightened with same trowel with force such that mortar gets pressed to its maximum extent. At this stage most important role plays the straight edge. Quality of plaster depends upon the quality of straight edge tool. In our local market straight edge that is mostly used by majority of the masons or contractors is made of steel and is available at cheap prices. However there is another straight edge available that is much more superior than typical steel one and that is made of aluminium sections. Aluminium straight edge is expensive as compared to steel straight edge however plaster straightened with aluminium straight edge has much more smooth finish as compare to steel straight edge.
Once mortar is applied, pressed and straightened next step is called trowelling. Trowel is tool dedicated for plastering and made of solid wood. However fiber/plastic trowels are also available in market at cheaper prices but are not recommended and should not be used. Troweling is a procedure that should be carried out with extreme care. Over trowelling can cause hairline cracks in plaster once it dries. After the plaster is trowelled it starts giving fine look however one final treatment is the application of foam. Foam should be applied a few minutes later after finishing trowelling to let the plaster settle. Foam should be applied in horizontal direction only in a line symmetrical manner. Some masons use foam in irregular or circular direction that destroys the final aesthetic look of finished plaster wall. Plaster after drying should be cured with water thrice a day for at least 10 days in summers or winters. Good plaster done by a good technical mason can get destroyed if curing is not done properly.
Another important point to remember during plastering is the mortar ratio and making of mortar. If walls are being plastered mortar ratio should be kept at 1:4 (1 cement 4 sand), whereas if ceilings are to be plastered ratio should be kept at 1:3. A detailed article on mortar ratios has already been posted and click here to learn about ratios. Sand should be used of best available quality for plasters which should be free of muddy or silt content and should not be too thick or too thin e.g if you are constructing your house in and around Lahore region, best sand available for plasters is Chenab. Ravi sand for a limited time period each year (Oct – Feb) is available in good quality otherwise it is not advisable for plasters, similarly if house is being constructed in or around Islamabad/Rawalpindi region best sand for plasters is Ghazi. Sand should be filtered using a steel mesh so that unwanted content stays out of mortar.
Workmanship plays very important role in plasters. It is a duty of contractor to assign team of masons on particular walls in such a way that no joint should appear and plaster be carried out in one go. While plastering external walls that are bigger in size with much more elements to be plastered other than plain walls such as concrete shades, designs, edges etc should be plastered first carefully in set square and plumb lines before plastering whole wall. Once these small elements in exterior wall are plastered, whole wall should be plastered in a single day in one go to avoid joints. If for any reasons it is impossible to complete whole wall in one go, work should be carried out in such a way that joint should be minimum visible.