METHODOLOGY - INTERNAL PLASTERING WORK

METHODOLOGY - INTERNAL PLASTERING WORK

A) Pre Plastering Checks.

1) It is recommended to carry out external plastering before internal plastering to prevent rapid drying and shrinkage of internal plastered surfaces.
2) Minimum gap of 7 days shall be maintained between completion of brick masonry and commencement of internal plaster application.
3) For application of cement sand plaster, thorough wetting of masonry should be done 2 days before commencement of plastering. The day prior to plastering, masonry surface shall be left to attain Saturated Surface Dry (SSD) condition.
4) Proper scaffolding shall be provided to allow easy approach to every part of the work, take all measures to ensure the safety of the work and working people. In no case, holes in masonry should be done for supporting scaffolding.
5) Level pads of size not less than 2” x 2” shall be made on the walls and if required on ceiling also to serve as finished reference level surface. The distance between level pads shall not exceed 6’ in any direction so that their surface alignment can be checked with the help of aluminum straight edge.
6) Level pads shall also be checked for vertical alignment with the help of plumb bob, for right angle with the help of right angle and for diagonal dimension of room with the help of tape.
7) At place of work where sufficient natural daylight is not available, artificial light shall be made available.
8) In case of level differences in adjoining surfaces, the same shall be made up before fixing of chicken mesh / fiber mesh.
9) Chicken wire mesh shall be fixed at the joints of BBM and concrete. Chicken wire mesh shall be 20 gauge, with 12 mm hexagonal holes and minimum 6” wide in the form of strip.
10) Chicken mesh after stretching shall be fixed at 9” intervals by drilling/punching holes in masonry and concrete and then nailing with metal washers. Minimum overlap for chicken mesh shall be 4”.
11) Instead of chicken mesh, fiber mesh can be used. Fiber mesh shall be stretched over the joints and fixed to walls with the help of mortar spots at every 9” interval. Joints of brick /block & RCC junction shall be applied with non shrink mortar e.g. CNS 50 or equivalent.
12) Surface preparation-
a) All the nails, binding wire, concrete projections and wooden piece shall be removed from concrete surface and brick masonry.
b) All the dust, oil spots, and green algae, if any, shall be cleaned from concrete and brick masonry surface with the help of wire brush.
13) It is recommended that all concrete surfaces where plaster is to be applied shall be applied with bonding agent. Bonding agents shall be applied as per instructions of manufacturer. If bonding agent is used, hacking of concrete surface shall be avoided.
14) Concrete surface should be roughened for proper bonding. Hacking should be done @ 1” c/c. (Minimum 60 to 65 hacks per Sq. ft.)
15) All electrical chases shall be properly rendered with non-shrink grout and application of chicken / fiber mesh over it and cured properly for 7 days before starting any type of plaster or curing compound can be applied for the same.
16) All the conduit drops shall be checked and concealed with plaster. All the ceiling points and wall points shall be checked for level and dimensions as per drawing or as per client’s requirement if any.
17) It shall be ensured that all electrical boxes are protected with plastic sheet packing before plaster.
18) Wooden / natural stone frame used for doors / windows should be protected before plastering.
19) It shall be ensured that all plumbing points are in proper location, line and level as per drawing. All plumbing chases shall be properly rendered with non-shrink grout and application of chicken / fiber mesh over it and cured properly for 7 days before starting any type of plaster.

B) During Plastering Checks:

Cement Sand Plaster
1) Mortar for plaster shall have minimum strength 3.5 MPa. For this 7.07 cm cubes shall be casted of cement sand mortar and shall be tested after well curing for 28 days.
2) Cement sand mortar shall be used as specified and it is recommended to carry out batching of sand by weight (batching if mix design for mortar is made)
3) In case, volume batching is to be done, calibrated boxes (pharmas) of required correct sizes shall be used. It
is recommended to apply 1:4 mortar for side wall and 1:3 mortar for ceiling in the absence of any specification. PPC or OPC-Fly ash combination is recommended, since reduced water demand and reduced heat of hydration

reduces shrinkage and thermal cracks respectively. Also PPC or OPC-Fly ash combination has better resistance against chemical and sulphate attack.

4) Water cement ratio shall be as per mix design (If mix design is available) or such as to obtain mortar mix of optimum workable consistency.

5) Mortar required for Plaster work shall preferably be mixed in half bag or full bag mechanical mixer and shall be carried out to required floor with the help of hoist and wheel barrows and unloaded in MS tray/bund and thereafter it shall be carted to actual work place.

6) While preparing mortar in mixer, cement and sand shall first be dry mixed and then water is added to it in appropriate quantity. Wet mix shall then be mixed thoroughly in mixer for a minimum period of 3 minutes. Fibers of 6mm length shall be used as specified by Q. A. Department. Plasticizers of approved make may be used as specified.

7) For small works, mortar can be made by hand mixing in MS tray / sunk / bunds. After dry mixing, wet mixing by hand shall be carried out for a period of at least 5 minutes.

8) The mortar mixed shall be utilized within 90 minutes of preparation and the same shall be used before recommended setting time of cement mortar, if retarders are used.

9) While applying plaster on walls, empty cement bags shall be placed on floor near walls and rebounded mortar fallen on bags shall be put back into mixed mortar before it sets and 10% additional cement should be added in that mix and remixing should be done before its use.

10) Use of dry cement shall be limited to finishing of edges only.

11) For internal plaster, average thickness of plaster shall not be less than 12 mm and not more than 15mm. The plaster above 15 mm thickness shall be done in 2 coats. Proper roughening to first coat shall be done before application of second coat for proper bonding and shall be cured for at least 3 days. Bonding chemicals can be used between the two coats for proper bonding.

12) Proper checking and supervision for plumb, line, right angle, measurement of openings after application of plaster should be done by site supervisor / engineer.

13) Thickness above 20 mm, if required shall not be built up in single operation. Thickness will be built up gradually using a combination of chicken mesh, fiber mesh, etc.

14) Electrical switch boxes shall be perfectly in line with plaster.

Gypsum Plaster:

1) Gypsum plaster thickness shall be restricted to 8 - 15 mm for walls and if because of undulations the final thickness is expected to be more than 15 mm, back coat is recommended before applying Gypsum Plaster.

2) Back coat of 6 to 10 mm thick (cement sand mortar) shall be applied on brick-work. Curing of back coat shall be done for 7 days before starting gypsum work. Back coat shall be in rich 1:4 cement mortar, which shall be preferably mixed in mixer by keeping proper control on w/c ratio.

3) Date of application of back coat shall be clearly displayed for proper monitoring of curing if cement sand plaster is done.

4) For ceilings, Gypsum plaster thickness shall be 6 to 10 mm thick.

5) Level strips of Gypsum shall be made through full height of wall and shall be checked for right angles.

6) Fixing of door frames shall be done with reference to gypsum thiyyas.

7) Gypsum plaster shall be applied only after back coat dries off completely.

8) All the preparation of RCC surface shall be done as per mentioned in procedures of cement sand plaster.

3) Post Plastering Checks:

Cement Sand Plaster:

1) After plastering work is complete, neeru / sanla shall be applied on plastered surface within 2 hours till the plaster is green and mason shall trowel the neeru / sanla surface to get smooth finish. Thickness of neeru shall not be greater than 1.5mm and neeru shall be cured.

2) It is recommended that 5 mm deep grooves shall be made (to limit the shrinkage cracks) on the finished neeru / sanla surfaces. Such grooves shall be spaced at 5’ both horizontally and vertically. After a period of 4 weeks, these grooves shall be filled with plaster of paris to ensure a uniform surface. It is applicable for back coats also.

3) Window frames, sills, door frames, electric switch boxes, fan boxes, taps, railings, plumbing fittings, glass etc. shall be cleaned immediately.

4) Wherever wall tiling is required, roughening of plastered surfaces shall be carried out for better bonding of

tiles. In such a case, no application of neeru / sanla / POP / gypsum shall be made on the plastered surfaces.

5) Plaster above the floor slab shall be cut in level to a height equal to height of skirting for fixing skirting tiles.

6) In toilets, plaster shall be cut at 300 mm above FFL to accommodate base coat for water proofing.

7) Date of plastering shall be clearly marked on the plastered surfaces to monitor curing process.

8) Curing shall be done so as to keep plastered surface continuously wet for a period of 7-10 days depending on type of cement and climatic conditions.

9) Curing shall be done carefully, by gently application of water on top of wall surface, so that water rolls down smoothly over plastered surface. Spraying of water jet with high pressure for curing shall be avoided since it will peel off the neeru / sanla.

POP / Gypsum.

1) In case of POP / Gypsum Plaster, no chasing shall be done after application of final coat on walls / ceilings.

2) Window frames, sills, door frames, electric switch boxes, fan boxes, taps, railings, plumbing fittings, glass etc. shall be cleaned immediately. Wooden sections for doors / windows should be cleaned thoroughly on same day. Otherwise, chances of white stains may occur over sections after polishing.