Often people
complain of cracks on walls after plastering works.Plastering plays an
important role in the construction of a building.Just as skin gives shape and
texture to the body and protects it from the harmful environment, plaster
protects the building from damage caused by salts, acid and rain in the
external environment.It also makes the building look beautiful and attractive.
Defect free
durable plaster,free from cracks or other defects can be achieved by
diligently following the correct construction practices.One of the reasons
cited for cracks is lack of proper cement sand ratio.Normally, for outside
plaster, the cement-sand ratio can be from 1:4 to 1:5, for internal plaster
from 1:5 to 1:6 and for roof plaster from 1:3 to 1:4.
For better
results, check that the mason uses a 1:4 rations mortar of cement and fine
sand. For coarse sand, the ratio can be changed to 1:6. However 1:4 mixes is
preferred for best results. Make sure that the mason has not prepared the mix
all together for the whole day. The mix must be prepared only in small
quantities so that it is used within an hour. If excess mortar is prepared, it
dries up due to evaporation and remixing deteriorates strength and increases
porosity.
The risk of
crazing cracks may be minimized by the use of relatively weak mix for finishing
coat, avoiding excessive proportion of very fine material in the finish coat
and avoiding excessive toweling so as to prevent the excess of laitance drawing
to the surface.A major precautionary measure to be under- taken prior to
plastering is remove loose mortar and grease from joints. All joints in the
masonry should be raked out to a depth of a least 12 mm with a hooked tool made
for the purpose while the mortar is still green and not later than 48 hours of the
time of laying.
Another
important task is that the wall should be wetted for a few hours. The walls
should not be soaked but only dampened evenly. Plastering on wet walls is
seldom satisfactory because key is not formed between the plaster and the background
surface.A good key is essential for successful rendering and for avoiding
cracking and crazing. In an ideal state the background should be in saturated
surface dry condition.
Addition of
water should be carefully monitored. Excess water will cause shrinkage as well
as low strength of plaster.Waterproof compounds if used should be uniformly
dispersed and mixed properly.When
plastering is done in two coats, the first coat should be left rough and open
from edge of the laying trowel and after it has been left long enough to setfirm, the surface should be combed or scratched to form a key for the second
coat. The first coat should be allowed to dry for three to five days before
subsequent coats are applied.
Use a
chicken wire mesh while plastering joints between the concrete work and
brick-work.Plaster should be finished with a wood felt. A steel trowel shall
not be used.Ensure continuous curing for 10 to 14 days. You may keep in mind
that the need for repairs arises due to negligence, use of unsuitable materials
and improper construction practices.Therefore, to save your buildings from
cracking adopt proper construction practices.
For more details,
Natural sand for the construction sector, manufactured sand, also known as M-Sand, is gradually gaining popularity in the construction industry
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