Pages

Thursday, 21 August 2014

Plastering with M-Sand (Manufactured Sand)

River sand is becoming a scarce commodity and hence exploring alternative to it has become imminent. Rock crushed to the required grain size distribution is termed as manufactures sand (M-sand). In order to arrive at the required grain size distribution the coarser stone aggregate are crushed in a special rock crusher and some of the crushed material is washed to remove fines. Following are the characteristics of M-sand and Natural river sand.

1.    The shape of the M-sand particle resembles with those of river sand particle. Flaky and elongated coarse particles are absent in the M-sand.
2.    M-sand is well graded and falls within the limits of grading Zone II sand, grading limits specified in IS 383 code. Code allows 20% fines less than 150 microns for crushed stone sands.
3.    The specific gravity is 2.63 for M-sand and 2.67 for river sand. Bulk density of M-sand and river sand are 15.1 and 14.5 KN/m3 respectively. Bulk density of M-sand is marginally higher than that of river sand. The pH of M-sand and river sand is 10.11 and 8.66 respectively.
4.    M-sand contains typical rock forming minerals like quartz, feldspar, mica group of minerals, etc., Rock forming minerals like quartz, feldspar, etc., are basically inert in nature. Mica group of minerals are not interfering in the cement hydration and strength development in mortars.   

a)    Surface preparation
Projected burrs of mortar formed due to the gaps at joints in shuttering shall be removed. The surface shall be scrubbed clean with wire brushes. In addition concrete surface to be plastered shall be pock marked with a pointed tool, The mortar shall be washed off and surface cleaned from oil, greases etc. and well wetted before the plaster is applied.

b)    M-Sand Mortar
The mortar of the specified mix using the M- sand with respect to IS 383,
1.    Mortar with M-sand show better workability and required lower water-cement ratio to achieve a specific flow value when compared to mortars with river sand.
2.    M-sand mortars show higher water retentively values.
3.    Compressive strength & flexure bond strength of mortar with M-sand is higher than that of the mortar with river sand 
4.    The utilization of M-sand leads to eco friendly construction and economic construction.                                                                                                                                            
c)    Application of plaster
                              I.        Ceiling plaster shall be completed before commencement of wall plaster;
                            II.        Plaster shall be started from the top and worked down towards the floor. All putlog holes shall be properly filled in advance of the plastering as the scaffolding is being taken down.
                           III.        When plastering on vertical surfaces, to ensure even thickness and a true surface, 15 X 15 cm plaster is done at regular intervals to serve as gauges (Bull marks), the surface of these gauged areas shall be truly in plane of finished plaster surface.
                          IV.        Mortar shall be applied in a uniform surface slightly more than the specified thickness and then brought to a true surface, by working a wooden straight edge reaching across the gauges, with small upward and side ways movement at a time.
                            V.        Finally the surface shall be finished off true with trowel or wooden float to attain sandy granular texture.
                          VI.        All corners, arises, angles and junction shall be truly vertical and horizontal as the case may be and shall be carefully finished. 
                         VII.        When suspended work at the end of the day, the plaster shall be left, cut clean to line both horizontally and vertically. When recommencing the plastering, the edge of the old work shall be scrapped cleaned and wetted with putty before plaster is applied to the adjacent area, to enable the two to properly joint together.
                        VIII.        Plastering work shall be closed at the end of the day on the body of walls and not nearer than 15cm to any corners are arises.   
                          IX.        Horizontal joints in plaster work shall not also occur on parapet tops and copings at these invariably lead to leakage.
                            X.        Curing shall be started as soon as the plaster has hardened sufficiently not to be damaged when watered, plaster shall be kept wet for adequate period.

d)    Precautions
                              I.        When ceiling plaster is done, it shall be finished to chamfered edge at an angle at its junction with a suitable tool when plaster is being done.
                            II.        Similarly when the wall plaster is being done, it shall be kept separately from the ceiling plaster by a thin straight groove not deeper than 6mm drawn with any suitable method with any suitable method with the wall while the plaster is green. 

e)    Scaffolding
Double scaffolding independent of the work having two sets of vertical supports shall be provided. The supports shall be sound and strong, tied together with horizontal member over which jaalies shall be placed.

f)     Finishes
The plaster shall be finished to a true and plumb surface and to the proper degree of smoothness as required and finishing shall be completed within half an hour of adding water to dry mortar.