Plastering and Pointing details

Plastering and Pointing

* Plastering is to give a smooth and decorative surface to walls and ceiling. It gives protection to

walls from rodents, insects and atmospheric action.

* Types of mortars used are mud plaster and lime plaster.

1. Mud plaster It is for low cost houses in which brickwork is also in mud. Ten per cent of clay

content should pass through 2.36 mm sieve and not less than 75 per cent should pass through 850

micron sieve. For making mortar, soil is mixed with water and left for 1–2 weeks. Then dried and

reduced to powder and mixed with 33 kg of chopped straw is mixed and plenty of water.

2. Lime plaster Hydraulic lime should be ground dry with sand in the ratio 1 : 2 and left for 2–3

weeks before regrounding and using. In case of fat lime the mix proportion used is 1 : 3 or 1 : 4

which are wet mixed. To improve binding property a kind of gum known as gugal is added to lime.

The gugal added is about 16 N/m3

. About 10 N of fibres of jute also added to per cubic metre of

mortar. The mortar so prepared is kept for weathering for two days.

3. Cement mortar 1 : 4 or 1 : 6 mortar is used for plastering external and internal walls respectively.

To make mortar waterproof, pulverized alum is added. Soap water containing 0.75 N of soft

soap/litre water is added.

4. Lime-cement plaster To improve plasticity and at the same time to maintain strength cement : lime

: sand mortar is used. Mix proportions of cement : lime : sand is usually 1 : 1 : 8 or 1 : 2 : 8. Fat

lime is preferred over hydraulic lime.

* For plastering new surface, all masonry joints should be raked to a depth of 10–15 mm and loose

particles removed with wire brush. The surface is washed and kept damp till plaster is applied.

* Plaster is usually applied in one, two or three coats depending upon the background. The first coat,

known as undercoat is 10–15 mm thick. The second coat, known as floating coat is usually 6–9 m

thick and finishing coat is 2–3 mm thick. External walls should have a minimum of 20 mm thick

while internal wall may be provided with 12 mm thick plaster.

* Plastered surfaces may be with the following finishes:

1. Smooth-cast finish 2. Sand-faces finish

3. Rough cast finish 4. Pebble or flint-dash finish

5. Strucco plastering.

* For plastering wooden surfaces wooden laths or metal lathes are used.

* The following defects may appear in plasters:

1. Unevenness 2. Rust stains

3. Efflorescence 4. Blistering

5. Cracking 6. Crazing

7. Flaking and peeling 8. Popping

* Pointing is the process of finishing mortar joints only to make the surface watertight. The joints are

raked to a depth of 10–20 mm after which they are filled with richer mortar. The mix proportion

used is 1 : 2 for lime mortar and 1 : 3 for cement mortar.

* The types of pointing are: Flush pointing, recessed pointing, V-pointing, weathered pointing, rubble

pointing, beaded pointing, struck pointing and tuck pointing.