All You Need To Know About Cement Plastering

By Author: Charles Julius
Total Articles: 2
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As you might already know that plastering the walls of your home is an important task because it renders a perfect finish to the wall surface and adds strengths to them. A single coat of plaster can conceal uneven surfaces, thus making your walls look even, smooth, and clean. Apart from that, it also provides a smooth base for painting, distempering, whitewashing, and colour washing. This helps the walls from rain and other environmental factors which could damage the structure.

The mixture is mixed with various ingredients such as plastic material or mortar which includes cement, lime, gypsum, fine sand, and water while making plaster. Today, mostly the cement plaster is used by plasterers in Melbourne to plaster the walls of the house. However, if you are unaware about the cement plaster then here is an article for you.

What is cement plaster?

A mixture of Portland cement, fine aggregates, and water make cement plaster. In order to create a cement-sand plaster, generally, OPC 43 and OPC 53-grade cement are mixed with sand in different proportions. Sometimes, PPC grade cement as well which are preferred ...
... in place of OPC grade cement for plastering because of their advantages over OPC cement.

However, applying plaster coats on a particular surface varies according to the requirement. While a single coat of plaster is adequate for the inner walls to achieve the desired finish. If you need a finer finish or require a 15mm thickness then only you will need 2 coat of plaster.

You will need a 3 coat finish where the first coat would be scratch or dash coat, for a smooth finish, second would be the base coat, and the last will be the finish coat. On the other hand, for the external walls, only two coats of plaster are required and the thickness of the plaster would be 12-18mm.

The required thickness of the plaster

The thickness of cement plaster depends on the composition and the surface to be plastered.

* The minimum plaster thickness is 10mm which is required to get a smooth surface on concrete walls.
* For the brick walls and uneven surfaces, the thickness would be 12-18mm.
* And for the surface that is superlatively uneven should have a thickness of at least 20mm.

The last and finishing coat should be of such minimum thickness to provide a sufficient body of material to adequately harden under site conditions. The rule says that the total thickness of 2-coat plaster should not exceed 20mm and the 3-coat one should not exceed to 25mm. While the 20mm plaster is usually used for the outer walls, a 15mm for the inner walls, and a 10mm is used for the ceilings.

Grading of sand for the cement plaster

This is very important to note that the sand you are using for the plastering purpose should be clean, sharp, suitably-graded, and free from impurities.

* For the final and base cost, the sand should 100% pass 2.36mm sieve and should not pass even 5% of 150-micron sieve.
* While for the finishing coat, the sand should not exceed to more than 1.18mm sieve.

Although to get a required grading, sometimes natural or crushed sand is blended together.

Cement sand ratio for the cement plaster

As mentioned earlier, different proportions of cement and sand are used to get a certain amount of plaster mix. There are some important factors that need to be considered when determining a proportion:

* Environmental conditions affecting wall and ceiling
* Type and grade of cement along with the sand
* At last, the location of plastering (interior or exterior)

The texture and the colour of the wall surface totally depends of the proportion mix of the finishing coat. After the proportion is decided, the ingredients are mixed using a cement mortar mixer. Where first the dry mortar is mixed and then the water is added to obtain the desired consistency.

In order to make the plaster mix, potable water is most suitable. The water mixed in the plaster mix should be free from chlorides and organic impurities such as silts, oils, alkalis, acids, and salts. These impurities are needed to extract because it weakens the mix.

The quantity of the water should be equal to 28% by weight of cement along with 4% by weight of all the aggregates for maximum strength. The materials should be saturated, nonabsorbent, surface dry so that the mix is workable and it gives maximum strength.

The amount of water to be added in the plasterwork should be 1:3 proportions where the 70% weight would be of cement. However, the quantity of water may vary depending on the following factors:

* Condition and nature of the fine aggregate
* Temperature and humidity at the time of plastering
* Richness of mix- whether it’s richer or leaner than 1:3
* Varying quantities of lime in the composite mortars

The quantity of water is taken as 20% of the total weight of cement and aggregates for regular residential plasterwork. Even to get the best possible results, the quantity of water should be added depending on the content of the cement mix and thickness of the plaster.

After the mix is ready, you can apply it by hand or instead use a cement plastering machine for a good finish. Mostly, manual plastering is great for working in small areas while the automated or semi-automated machines can be used for larger homes and offices.

Curing the plaster

Curing a plaster is a very important step because it reduces surface cracks and at the same time adds strength to the wall. Plaster should be cured for more than 24 hours after the plastering work. After the plastering is done, the surface should be kept wet for about 7 days. Also, there should be a gap of at least 7 days between the first and second coat. Moreover, each coat should be kept damp continuously for about 5 days. Finally, you need to make sure that the base coat is evenly dampened before applying the next coat.

In cold weather conditions, the plaster needs to be cured for a longer period of time due to the humidity. While the weather conditions that are less humid such as in summers, the curing process should start soon as the cement mortar tends to show evidence of setting.

After the plaster is fully set, you get a beautiful, even, and smooth surface to get it painted from the best painters in Melbourne.