Saturday, 25 October 2014

How To Avoid Cracks After Rendering Or Plastering your Walls

How to avoid cracks on walls during finishing

Today on Building Contractor secrets, I will be sharing a few tip on how you can avoid Cracks on your walls after Rendering or Plastering. I feel this is important because most times you discover cracks begin to appear on walls just a few months after rendering is done.


The aim of this post, is therefore to give us an insight on the preparatory steps for plastering or rendering 

Before I go into this post properly, I'll like us to have some idea of a few keywords.

What Is Rendering?
As we all know, Rendering is also known as "Plastering", it is an in expendable part of the finishing touches in building construction projects. Its therefore the aspect of construction that Presents the beauty or aesthetics of a building and as such, any error made during this stage maybe very difficult or impossible to correct.


It is important for the resident engineer or site engineer to always be available on site in order to ensure that the right mix ratio is used by mixers or casual workers.

This is because when a poor mix ratio is used, then the chances of cracks appearing On the surface of walls becomes inevitable.

Also, care should be taken when making the choice of sand to be used for plastering processes. It is observed that bricklayers would rather prefer the sticky soils since they are easily applied without much force. This however does not mean that sticky sands are the best for plastering.

The sand to be used in plastering must be clean
It should not have dirt (like plant parts)
It is advisable to sieve sands with dirt before using them for plastering
To get a good plastering job, tell the masons (bricklayers) to apply gauge.

Gauge is just a term used by masons/bricklayers which is using a thin material especially wood with rope to mark out how the Cement mortar will spread round the surface of wall of the building to achieve perfectly vertical Walls.

Block works are usually not done to perfection especially when the bricklayers are not very good. Often times, the blocks will not stand perfectly vertical, therefore some areas will require more mortar filling to others to compensate for the bad areas, so gauging is what you do to achieve a perfect plane. In doing this, some areas will require more mortar 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 finishing coat 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 Cracks On Walls After Rendering/Plastering

(1) impatience of the work men:- 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 given 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 be properly 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. But when the opposite is the case, then the chances of cracks on the walls becomes very high. This is because, lets say the sand had some leaves on it, after the cement is been mixed and applied, drying will take place. When the cement mortar is fully dried, the leave will begin to erode and as it erodes, it leaves holes on the wall.

(3) Poor cement in mix:- When the cement is not adequate, the plastering mortar will be a poor one and this may not favor the ability of the cement to bond well with the wall. And as time goes, cracking begins to appear on the walls.

 (4) Pipe Holes left by Plumbers and Electrician-The pipe holes where pipes are placed in should not be covered immediately with 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, and then apply plaster and leave to dry till next day or more before final coating to finish.

(5)Poor workmanship- Get a good bricklayer/mason for this project and ensure the contract agreement is not daily pay because if you bargain for daily pay, then your job will be done with hurry and there may not be time to think about factor of safety



(6)Dirt 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, and then use brush to run the cement along the lines of the plaster.

listed above are some of the reasons why we may have cracks on walls after plastering, however, feel free to criticize this post and make better suggestions.

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