Posts Tagged ‘cement sand ratio’

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Preparing for plastering and how to avoid plaster cracks

Plastering is the most important part of the finishing job in a building project, whatever error
made during plastering may be difficult to correct,because after it, is just to paint and fix
other accessories.
Plastering takes a lot of cement and is important the mix ratio quality is not reduced because
of the consequences.
Care should be taken right from the type of sand you ordered, bricklayers prefer the sticky ones
because they bond easily without applying too much power to splash the mortar on walls (though
this does not automatically means is the best to use.)
The sand must be clean, should not have dirts, and any sand with dirts should be sieved.
As said adequate numbers of cement with standard cement and sand ratio should be maintained.
Is also important you get good hands to do the jobs for you.

Plaster cracks leading to an opening a door.

To get a good plastering job, tell the masons to apply guage. Guage is just a term used by
masons/bricklayers which is using a thin material especially wood with rope to mark out how the
plastering will spread round the surface of wall of the building to achieve perfectly vertical
walls. Blockworks are usually not done to perfection especially when the bricklayers are not
very good, often time, the blocks will not stand perfectly vertical, therefore some areas will
require more mortar filling to others to compensate for the bad areas, so guaging is what you do
to achieve a perfect plain. In doing this some areas will require more mortars than the others.
Plastering is usually applied between 15mm to 25mm, but some areas may require more mortar, in
such cases, apply cement and sand, leave to dry till the next day before you apply the finished
coating for a smooth surface. Leave the area you filled till the next day and allow to dry
before you apply the final coat on it.
I prefer a mixture ratio of 1:5-1:6 for cement, sand mix.
Causes of plaster cracks

Cracks in building

Plaster cracks as a result of electrical works

(1) Deep filling not allowed to dry properly-Don’t give plastering project to your
masons/bricklayers on per day payment because when you pay for the job done per day, a mason
must finish up the portion giving to him before the day runs out, so he will fill and won’t wait
for it to get dried before applying the final coat. The plaster filling requires minimum of 6
hours to get dried, but a mason that is expected to be paid on daily basis will not have the
luxury to leave such portion till the next day so that he can take home his pay, hence the
plaster will be applied before the filling get dried, this will inevitably cause cracks. The
plaster filling will shrink and contract in the process of drying, this will cause it to leave
strips of cracks inside which will allow air to fill the space and inevitably will also affect the plaster
finish on top.
(2)Bad plaster sand-The sand is supposed to be fine with no impurities and should be able to bond
well with the cement.
(3)Shortage of cement-When the cement is not adequate, the plaster will not bond well and will
results in cracks.
(4)Pipe holes left by plumbers and electrician-The pipe holes where pipes are placed in should
not be covered immediatelywith plaster, because of the space, the holes are better not left to
the plumbers and electrician but there should be a mason/bricklayer on site that will be
responsible for filling back the holes. First fill the gaping holes with broken blocks, then
apply plaster, leave to dry till next day or more before final coating to finish.
(5)Poor workmanship-Get a good bricklayer/mason for this project.
(6)Dirts and impurities in plaster sand will also affect the outcome of your plastering.
When you notice a minor crack, apply cement slurry by that I mean mix pure cement with water,
then use brush to run the cement along the lines of the plaster.