METHOD STATEMENT
FOR
EXTERNAL PLASTERING WORK
Material:
Cement:
For external plastering, following checks are important.
1) Cement shall be OPC 43 Grade or PPC and not more than 8 weeks old. PPC or OPC-Fly ash combination is recommended since reduced water demand and low heat of hydration reduces shrinkage and thermal cracks.
2) Cement shall be free from lumps.
Natural Sand:
Sieving of sand should be done for mortar of plasters. Gradation of sand for use in plaster mortar as per below table.
IS SIEVES Percentage passing by mass
10 mm 100 4.75 mm 100 2.36 mm 90-100 1.18 mm 70-80 600 microns 45 to 59 300microns 15 to 30 150 microns 0 -10
If grading of sand falls outside the specified limits as above, the required grading may be obtained by screening.
Silt content should not exceed 7 % by volume (3% by weight) .
Water:
Water must meet the requirements of IS 456:2000 and should be tested at a third party laboratory
to check the compliance before use.
Admixtures:
For admixture following checks are important
Brand and type of admixtures must be approved & standardized
Density and chloride content should be checked before approval.
TOOLS :
A. Trowels, Line Dori, Level Tubes, Plumb Bobs, Measuring Tape, Spirit Levels, Aluminium Straight Edge, Right Angles.
B. Chipping tools, Mason Trowel, Mason hammer, Levelling thread, Mason Brushes, Mortar Boxes.
Procedures to be followed for 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. steel scaffolding as is applicable up to 12 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) Surface Preparation
All the nails, binding wire & concrete projections shall be removed from concrete surface and brick masonry.
All the dust, oily spots, and green algae, if any, shall be cleaned from concrete and brick masonry surface using wire brush.
6) Bulges from concrete surfaces on external beams shall be grind so as to bring entire masonry surface as well as outer surface of members in one line. (chipping is not allowed)
7) Joints between masonry and concrete members shall be filled with non-shrink mortar e.g. CNS – 50 or equivalent or repair mortar or polymer modified mortar, 2 days in advance of starting of plastering and then cured for next 2 days till external plastering work starts.
8) green net should provide on external sides of scaffolding to prevent rapid drying and shrinkage cracks of plastered surfaces due to wind or sunlight.
9) 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.
10) Similar line dori stretched over entire surface at 1M distance apart horizontally by driving pegs at every floor. Line dories shall also be stretched horizontally at 1 M distance apart vertically to form a grid.
11) 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, 12) Level pads of size not less than 2”X2” in size at 1M 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.
13) 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.
14) PVC mesh /expanding metal shall be applied on joints of Brick / Block Masonry and concrete in double layer. It 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”. For every small block work i.e. up to 1m the mesh has to be provided at both RCC joint i.e. bottom & top.
15) RCC / PCC coping for all sills and parapet tops shall be completed before commencement of external plaster.
16) Masonry chiselling for electrical conduits or any other purpose shall be sealed with non-shrink material with PVC mesh fixed over it, well before plastering of the surface.
17) The AAC 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 (1:4).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 (1:4).
4) Mortar required for plaster work shall be mixed in half bag or full bag mechanical mixers only. 5) While preparing mortar mix, 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. Fibre (PP based 3’s recron 125 gm per bag), added in mortar shall be well separated by hand before putting them in rotating drum along with water.
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 (pidiproof Lw+ 200 ml per bag of cement)
8) Mortar shall be used before initial setting time of mortar which is approximately 90 minutes.90 mi 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 present 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. Plaster should rough With 16 gauge wire, 2mm deep & maximum distance between two groves should not more than 10mm.
15) All dead wall plaster has to be done in one day from top to bottom. if it cannot be finished then proper sequence/planning of first coat of plaster has to be done along with project in charge so every layer/patch of plaster has to be cured minimum three days .
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 along with bonding agent shall be applied over first coat before applying second coat as a bonding agent .
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 10 mm and the same shall be finished as per requirement.
19) All dead wall plaster has to be done in one day from top to bottom . if it cannot be finished then minimum three days curing has to be done for above plaster before start the below floor’s plasters. 20) Grooves, if any, shall be of uniform depth and width throughout.
21) 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.
22) Window reveals (external horizontal portion of window sill) shall be given outward slope to drain out the rain water.
23) 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.
24) 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.
25) Chajjas 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.
26) All external ornamental features shall show equal offsets, line, level, right angles etc.
27) In exceptional cases, where extra thickness of plaster is required , the same shall be applied in 2 to 3 layers, with proper anchoring by nails & 16 gauge wield mesh / expanded metal etc.
28) Apply a gudgudi/dabba coat finish over plaster with 3mm sand evenly it gives uniformity in texture and has better resistance to weathering effect.
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 climatic conditions.
Tolerances:.
I External Plaster
1 Mechanical anchorage -
Hacking 40 Nos./Sqft 20mm x 5mm x 2mm deep
2 Chemical Anchorage /
Bonding Agent Coverage & duration as per the manufacturers specification 3 Proportion - First Coat 1:4 (1 part Cement & 4 part of
sand excluding bulkage)
4 Second Coat 1:4 (1 part Cement & 4 part of
sand excluding bulkage) 5 No of coats to be
provided 2 Or as specified in the BOQ or WO
6 Maximum thickness for
1st coat 12 - 15mm
If thickness is more than 15mm, shall be done in two coats
7 Maximum thickness for
2nd coat 8 - 10mm
If thickness is more than 15mm, shall be done in three coats
8 Plumb / verticality In visual plumb & in true line 9 Right angle to adjoining
wall <2mm in 600mm
10 Cracks No
11 Crazing No
12 Hollowness No
13 Pre application wetting 2 Days Minimum
14
Surface undulation - when checked with 3m Aluminum straight
3mm in 3m No visual undultation
15 Minimum plaster
thickness 20mm
16 Grouting of RCC &
Masonry junction 3 days prior to plaster. Filled with non shrink grout 17 Application of Chicken
mesh 1 days prior to plaster, PVC mesh in double layer
18 Type of Cement PPC
19 Sand grain size for sand
facing Passing through 2.36mm sieve & uniformly distributed 20 Grooves, Patta, Cornices In level of each other, variation in measurement + or - 10mm
21 Joint of two plaster joint Joint in level & in straight line, even distribution of grains of sand facing 22 Gap between 1st and
2nd coat Minimum 3 Days
23 Curing Minimum 10 Days
24 Hole / recesses in
plaster for scaffolding Not acceptable accepted for high rise as approved by EIC
