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.