METHODOLOGY OF EXTERNAL PLASTERING WORK

 METHODOLOGY OF EXTERNAL PLASTERING WORK

Pre Plaster Checks:

1) Minimum gap of 7 days shall be maintained between brick masonry and external plaster.
2) Sequence of plastering shall be decided in advance. Joints of plaster shall be kept on centre of RCC members such as beams / columns.
3) It shall be ensured that scaffolding material to be used for the plastering should preferably be double scaffolding. H- Frames or equivalent is recommended for the same. Both steel scaffolding as well as wooden scaffolding is applicable up to 12 to 15 storey height. For larger heights, scaffolding shall be designed from the designer and the same shall be used.
4) No holes shall be made in masonry for supporting scaffolding.
5) Bulges from concrete surfaces on external beams shall be chipped of so as to bring entire masonry surface as well as outer surface of members in one line.
6) Joints between masonry and concrete members shall be filled with non shrink mortar e.g. CNS – 50 or equivalent or rich cement sand mortar in proportion 1:3 with fibers (polypropylene/ polyethylene) added to it, 2 days in advance of starting of plastering and then cured for next 2 days till external plastering work starts.
7) Curtain cloths or plastic sheets may be provided on external sides to prevent rapid drying and shrinkage cracks of plastered surfaces due to wind or sunlight.
8) Pegs are driven diagonally at the corner edges on each floor starting from the top most floor of the plastering area and line dori shall be fixed on pegs keeping it fully stretched.
9) Similar line dori stretched over entire surface at 6’ distance apart horizontally by driving pegs at every floor. Line dories shall also be stretched horizontally at 6’ distance apart vertically to form a grid.

10) In addition, line dories also stretched horizontally as well as vertically along the sills, soffits and jambs of openings, windows, ventilators , chajjas, and any projections kept for architectural effects,
11) Level pads of size not less than 2”X2” in size at 6’ c/c (i.e. at every vertical line dori.) both horizontally and vertically shall be made on the wall to serve as reference level surface for base coat. Levels pad shall be checked for plumb and right angles.
12) Drain spout in toilet and sunks shall be fixed.
13) Plumbing pipe holes shall be made in masonry, diameter of hole being 1” more than the pipe diameter all round.

14) All terrace outlets (bends) as well as other plumbing outlets shall be placed within the holes, and holes shall be renders with non shrink grout.

15) Chicken mesh /fiber mesh /expanding metal shall be applied on joints of Brick / Block Masonry and concrete. Chicken wire mesh shall be of 20 gauges, with 12mm hexagonal holes and minimum 6” wide in the form of strip, 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”

16) Surface Preparation-

a) All the nails, binding wire, concrete projections, and wooden pieces shall be removed from concrete surface and brick masonry.

b) All the dust, oily spots, and green algae, if any, shall be cleaned from concrete and brick masonry surface using wire brush.

17) RCC / PCC coping for all sills and parapet tops shall be completed before commencement of external plaster.

18) Masonry chiseling for electrical conduits or any other purpose shall be sealed with non-shrink material with chicken mesh fixed over it, well before plastering of the surface.

19) The brick masonry shall be wetted thoroughly from outside on the day prior to day of application of external plaster so that masonry surface is moist at the time of external plaster.

During Plaster Checks:

1) Mortar for plaster shall have minimum strength 3.5 MPa.

2) Cement sand mortar shall be used as specified and it is recommended to carry out batching of sand by weight as per mix design.

3) In case volume batching is adopted, calibrated boxes of required correct sizes shall be used. Batching shall be done as per recommended proportions in mix design.

4) Mortar required for plaster work shall be mixed in half bag or full bag mechanical mixers only.

5) While preparing mortar mix, cement, fly ash 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, if added in mortar shall be well separated by hand before putting them in rotating drum.

6) Water cement ratio shall be such as to obtain mortar mix of optimum workable consistency.

7) Water-proofing compound shall be added to mortar in adequate quantity as recommended by water-proofing compound manufacturer. If water-proofing compound is in powder form, the same shall be added to mortar during dry mixing of mortar and if in liquid form, the same shall be added to water during wet mixing of mortar.

8) Mortar shall be used before initial setting time of mortar which is approximately 90 minutes.

9) External plaster shall be applied in two coats. Thickness of first coat shall not exceed 15 mm.

10) Empty cement bags / plastic sheets shall be kept on ground near the face of building and rebound mortar collected on bags shall be poured in the mixer for reuse by adding 10 percent extra cement. The entire process shall not exceed 90 minutes.

11) In no case, joint of external plaster shall be kept on parapet wall, since that joint is highly susceptible for seepage of rain water through parapet wall and ultimately to the rooms below. Parapet top plaster shall continue at least 1’ inside the terrace.

12) Thickness of plaster on parapet top shall not exceed 20 mm and plaster top shall be given slope 15 mm inside to drain off rainwater inside the terrace.

13) First coat of plaster shall be sufficiently roughened for bonding of second coat over it.

14) First coat shall then be cured for minimum 3 days to maximum 5 days and then finishing coat shall be applied over first coat.

15) If the time gap between application of first coat and second coat exceeds 5 days, cement slurry shall be applied over first coat before applying second coat. Instead bonding agent as approved by LODHA QA/QC Department can be applied for the same.

16) Grills, wherever provided, shall be fixed prior to application of second coat.

17) Bonding agent shall be applied to horizontal joints of first coat and finishing coat for proper bondage. It prevents seepage of rainwater through horizontal joints. Horizontal joint as well as vertical joint should be strictly kept on RCC members.

18) Thickness of second coat shall not exceed 8 mm and the same shall be finished as per requirement.

19) Grooves, if any, shall be of uniform depth and width throughout.

20) Finishing coat shall be applied in such a way that all vertical lines of windows, balconies, common dividing

walls shall match at all levels. Also sill and soffit levels of openings / windows / ventilators at any floor shall be in one line.

21) Window reveals (external horizontal portion of window sill) shall be given outward slope to drain out the rain water.

22) Drip moulds (Pani Patti) shall be provided to all the chajjas as well as projections. Pani Patti shall be at 5 mm thickness and 35 mm in width or as per details given in the drawing.

23) Chajjas shall project minimum 6” beyond the window openings on both sides. If the drawing does not show such projections, then such requirement shall be posed before the concerned architect and work shall proceed with his suggestions or alterations.

24) Chajja top plaster shall be rounded to merge inside the external plaster to prevent ingress of rain water providing cut patti or as specified on drawing.

25) All external ornamental features shall show equal offsets, line, level, right angles etc.

26) In exceptional cases, where extra thickness of plaster is required (2” to 3”), the same shall be applied in 2 to 3 layers, with proper anchoring by nails / chicken mesh / expanded metal etc.

Post Plaster Checks:

1) Wherever tiling is to be done at a later stage, roughening of plastered surfaces shall be carried out for better bonding of tiles.

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

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

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