Work Procedure Specifications for Internal and External Plaster works

Srinivasan

Administrator
Sep 7, 2017
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mumbai
Work Procedure Specifications for Internal and External Plaster works

SCOPE

This specification covers plaster work for both interior and exterior surfaces of masonry and concrete.

Materials

Cement and water shall be as specified in specifications for concrete works.
Sand for plastering and pointing shall conform to IS 1542. Sand shall be hard, durable, clean and free from adherent coatings and organic matter and shall not contain silt, clay or pallets. Sand shall not contain impurities .
Fine sand shall be obtained from river and shall be clean, sharp and free from excessive deleterious matter. The sand shall not contain more than 8 percent of mud and silt as determined by field test with a measuring cylinder.


BASIC REQUIREMENT

Texture Finish shall be applied with CM 1:3. Ornamental treatment in the form of horizontal or vertical rib texture, fan texture shall be applied by means of suitable tools to freshly applied plastered surface, as approved by Engineer-in-charge.

SCAFFOLDING

Only steel scaffolding shall be used. Scaffolding shall be properly planned and designed by the CONTRACTOR. It shall be approved by Engineer-In-Charge before commencement of work. Double scaffolding, sufficiently strong so as to withstand all loads likely to come upon it and having two sets of vertical supports, shall be provided. Where two sets of supports are not possible, the inner end of the horizontal scaffolding member shall rest in a hole provided in the header course only. Only one header for each member shall be left out. Such holes shall be filled up immediately after removal of scaffolding.

For internal plastering, scaffolding shall be erected independent of walls. No member of scaffolding shall be allowed to be housed in the walls being treated with plaster. Scaffolding for external plaster shall be supported independent of walls as far as possible to avoid patchy appearance.

The following measures shall be considered while erecting of scaffolding.
  1. Sufficient sills or under pinning in addition to base plates shall be provided particularly where scaffoldings are erected on soft grounds.
  2. Adjustable bases to compensate for uneven ground shall be used.
  3. Proper anchoring of the scaffolding/ staging at reasonable intervals shall be provided in each case with the main structure, wherever available.
  4. Horizontal braces shall be provided to prevent the scaffolding from rocking.
  5. Diagonal braces shall be provided continuously from bottom to top between two adjacent rows of uprights.
  6. The scaffolding shall be checked at every stage for plumb line.
  7. All nuts and bolts shall be properly tightened.
  8. Wherever steel tubes are used care shall be taken that all the clamps/ couplings are firmly tightened so as to avoid any slippage.


PREPARATION OF SURFACES

The surfaces shall be cleaned off all dust, mortar droppings, traces of , oil, efflorescence and other foreign material by wire brushing, hacking, chiseling, etc. If the Engineer-In-Charge is not satisfied with the roughening achieved by these methods, he may order other methods such as washing with acid etc
Joints shall be raked to a sufficient depth.. Care shall be taken, not to damage masonry edges while raking.
All surfaces of concrete, old plaster and masonry shall be roughened sufficiently for bond.
Soft or crumbling masonry work and other surfaces shall be dismantled and remade .
In case of concrete work, projecting burrs of mortar formed due to the gaps of joints in shuttering shall be removed. Such surface shall be scrubbed clean with wire brushes. The surface shall be marked with a pointed tool at spacing of not more than 50mm centers. The marks shall not be less than 3mm deep to ensure a proper key for the plaster.
All surfaces to be plastered shall be thoroughly wetted for 24 hours before commencing plaster and shall be kept damp during the progress of work. Wetting shall be uniform.
To avoid cracks at the junction of concrete with masonry work, the plaster shall be reinforced at such junctions by fixing standard wire mesh (6 x 6 x 6/6) as directed by the Engineer-In-Charge. The wire mesh shall overlap concrete and masonry surface by at least 150mm.
The preparation of surfaces shall be inspected by the Engineer-In-Charge. Plastering shall not be commenced, until the preparation of surfaces is approved by the Engineer-In-charge.


CEMENT PLASTER

General

Cement mortar shall be prepared by mixing cement, sand and water in specified proportions. The mortar shall be used as soon as possible after mixing and before it has begun to set and in any case within 30 minutes after the water is added to the dry mixtures. Mortar unused for more than 30 minutes shall be rejected and removed from the site of work.

Proportioning

The unit of measurement for cement shall be a bag of cement weighing 50 Kgs and this shall be taken as 0.035 cubic meter (M3). Sand in specified proportion shall be measured in boxes of suitable size. It shall be measured on the basis of its dry volume. In case of damp sand its quantity shall be increased suitably to allow for bulkage.

Mixing

The mixing of mortar shall be done in mechanical mixer operated manually or by power. The Engineer-In-Charge may, however, relax these conditions at his discretion, taking into account the nature and location of work, practicability of the use of these machines. For items, where the mixers are not to be used, the CONTRACTOR shall take the approval of the Engineer-In-Charge before the commencement of work

Mixing in Mechanical Mixer

Cement and sand in specified proportions shall be mixed dry thoroughly in a mixer. Water shall then be added gradually and wet mixing continued for at least one minute. Care shall be taken not to add more water than that which shall bring the mortar to the consistency of a stiff paste.
Only the quantity of mortar which can be used within 30 minutes of its mixing shall be prepared at a time.
Mixer shall be cleaned with water each time before suspending the work.


Hand Mixing

The measured quantity of sand shall be leveled on clean water tight platform and cement bags emptied on top. The cement and sand shall be thoroughly mixed dry by being turned over and over, backward and forward, several times till the mixture is of a uniform colour. The quantity of dry mix which can be used within 30 minutes shall then be mixed with just sufficient quantity of water to bring the mortar to the consistency of a stiff paste.

CEMENT PLASTER WITH WATERPROOFING COMPOUND

Water proofing compound shall conform to IS 2645 . The compound shall be well mixed with dry cement in the proportion of 2% by weight or as recommended by manufacturer.

SEQUENCE OF OPERATIONS

For external plaster, the plastering operations shall be started from the top floor and carried downwards. For internal plaster, the plastering may be started wherever the building frame, roofing, and brick work are ready.
The first under layer shall be applied to ceilings. After the ceiling plaster is complete, plastering on walls shall be started.


SAND FACED PLASTER (20 mm thick)

First coat

The first coat shall be 12mm thick of 1:4, cement-sand proportion by volume. Guide stripes 150mm wide and of suitable length shall be first put up on the surface for the first coat. These guide strips shall be brought to absolutely plumb vertically and to the same plane horizontally all through.
These guide strips shall be put up sufficiently earlier, so that at the commencement of plaster, these guide strips shall have sufficiently hardened. The plastered surface then shall be firmly pressed to a uniform plumb and plane. The surface shall then be sufficiently scratched to receive the second coat. The surface of the first coat shall be thoroughly combed, so that 5mm deep grooves at 12mm apart are formed, when the mortar is in the plastic stage. The surface shall be cured for at least 3 days.


Second coat

Sand used for the second coat shall be sieved. Sand passing through 3mm sieve shall be used. The sand shall be of uniform size.
The second coat shall be 8mm thick of 1:4, cement sand proportion by volume. The second coat shall be struck uniformly over the first scratched coat and firmly pressed and leveled using a batten. The surface shall than be firmly trowelled and sponge floated to remove excess moisture and to bring the sand to the surface.
A sponge dipped in cement water shall be used with circular motion to get the sandy appearance.
The surface thus prepared shall be uniformly roughened for texture by running a fine wire brush lightly over the surface, as per the instructions of Engineer-In-Charge.
The surface of the plaster shall be kept moist, for a minimum period of 7 days and shall be protected from sun rays.


GYPSUM PUNNING

Material shall be as approved by Engineer-in charge.work involves roughen plastered surface with light wire brush, taking care to see that the plaster does not fall off during such roughening operation.
Applying plaster of Gypsum in two coats having thickness of 8 mm each.
Smoothening the surface with trowel to obtain a uniform surface without any waves.
Permissible variations in final level of plaster: + 1 mm per meter in vertical plane.
All undulations in final level of plaster shall be checked with straight edge, spirit level and line strings (stretched).
Any undulations exceeding permissible limits shall be rectified by CONTRACTOR at his own cost.
Any hollowed plaster detected by tapping shall be rectified by CONTRACTOR at his own cost.



DAMAGE RECTIFICATION

Any cracks, damages, any part of work which sound hollow when tapped or found damaged or defective otherwise shall be cut out in rectangular shape and redone as directed by Engineer-In-Charge at no extra cost.

POINTING

Surface Preparation

The joints of the masonry either brick stone or laterite to be flat pointed shall be raked to a depth of at least 12mm. Raking shall be done carefully and on no account shall any chipping of the masonry be permitted. In new work the raking out shall be done when the mortar in the joint is still green and fresh.
Before pointing is commenced, the whole raked surface shall be properly cleaned with wire brushes, washed with water and kept well wetted.


Application

Unless stated otherwise, the mix for pointing shall be of 1:2 (cement – sand) proportions. It shall be properly worked with sufficient water to produce a smooth paste.
The mix shall be pushed into the joints and superfluous mortar properly removed with a trowel.
The pointing lines shall be regular and uniform in breadth and shall be finished flush, raised etc as specified.
The edges of the pointing shall be cut off parallel so as to leave well defined lines.
In recessed pointing, the mortar shall be struck off, with a trowel and the work left, showing the natural irregularities, in line and surface of the stones themselves.
In case of raised pointing, it shall project from the wall facing with its edges cut parallel, so as to have a uniformly raised band of about 6mm and width 10mm or more as directed, showing the natural irregularities in line and surface of stones themselves.
The pointing shall be kept wet for 7 days or as directed by Engineer-In-Charge.


CURING

All plaster and mortar works shall be kept damp continuously for a minimum period of 7 days after the application of the final coat.
Curing shall commence, 24 hours after the plaster is laid.
To prevent excessive evaporation on the sunny or windowed sides of buildings in hot dry weather, matting or gunny bags shall be hung over the outside of the plaster and kept moist.
In case the plaster/mortar cracks through neglect of watering or any other fault of CONTRACTOR, the plaster shall be removed and redone at his cost.