Different categories of sands and their applications

The sand is mainly applied for rock particles which mainly vary in grain size among 2 mm and 1/16 mm. In composition, they are primarily an oxide of silica SiO2.

Mineralogically, they mostly include broken grains of mineral Quartz (SiO2) that is formed due to the crashing of sandstones and equivalent rocks.

Categorization of Sands: Sands are classified variously on the basis of their Based on the mode of origin, composition, and grain size, the sands are differently categorized.

The mode of origin: With adherence to the mode of origin, there are three types of sands like pit sands, stream sands and marine sands..

The pit sands are generally sharp and angular in outline. Winds generally deposited them and develop accumulations in soils covered by clays. Good quality mortars can be produced from these sands by purifying and cleansing them properly.

The river sands come about large accumulations along the base and banks of all the rivers in plains and semi-hilly areas. The shape of the sand grains in river sands appear almost round (because of significant movement in river waters).

These do not contain clay, salt encrustations, and organic impurities. So, these are frequently utilized to produce mortars, plasters, and concrete.

The marine sands are found on beaches and along the seashores. Similar to river sands, they comprise of rounded grains of quartz. There are some problems with these sands as their grains are mostly wrapped with coatings of salts from sea water.

These salts can’t be separated easily. So, if these salts are utilized with mortars or concrete, a reaction occurs with the binding materials and produce lots of difficulties. Beside, the salt encrustations are often hygroscopic, it means they consume moisture from the atmosphere.

It also leads to delayed setting, dampness. Besides, efflorescence may also happen in mortar or concrete that is formed with these sands. Therefore, the quality of marine sands is substandard and should not be recommended. But, in case of requirements, marine sands should be cleansed perfectly prior to utilize them.

In order to learn how sand is categorized on the basis of composition and grain size, go through the following construction article.

Source: civilseek.com

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Published By

Rajib Dey

www.constructioncost.co

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Some vital plastering defects and remedies to resolve them

Besides, cracking, there may be other flaws with plastering. John Roxburgh who performs lecturer at The Concrete Institute’s School of Concrete Technology, highlights the following points for plastering defects as well as proper solutions for resolving them.

1. Debonding: Plaster, particularly very thick layers, is set to debond from the wall if the exterior skin compresses at a diverse rate except for the plaster touching with the wall. It will be the outcome of insufficient substrate formation.

Areas greater than regarding the size of a plate should have been eliminated and substituted with the following :-

• Cleaning filthy or greasy wall surfaces completely.
• Maintain the exact moisture content for the walls.
• Prior to plastering, apply a cement slurry or spatterdash coat.
• Apply bonding liquids and abide by the method suggested by the manufacturer.

2. Hardness Scarcity: There do not exist any specifications for the hardness or strength of plaster, but soft plaster happens due to the followings:

• Inadequate cement.
• The sand contains unnecessary quantities of dust (in excess of 15% by mass going through the 0,075mm sieve).
• The utilization of a mix with sub-standard water-retention properties.
• The inclusion of supplementary water too long after first mixing (a practice called as re-tempering).

Sometimes, It becomes necessary to provide a slightly lower plaster that occasionally demonstrates vital cracking or debonding, as compared to strong one.

3. Instant drying: Normally, extreme early moisture loss occurs due to the following:

• Evaporation may occur if plastering is done in sun and wind.
• Suction into the walls, when the masonry units are not moistened.
• Apply bad grade sand that does not contain fine material (below 5% by mass passing the 0,075mm sieve).
• Refrain from applying building lime or a masonry cement when there is no fine material in sand.

4. Grinning: Grinning means when the mortar joints are evidently seen through the plaster. It occurs due to the variation in suction among the masonry units and the mortar, along with extraction of mortar joints.

To get rid of grinning, use an undercoat or a spatterdash coat prior to plastering.

5. Expansion: It contains swelling, softening, layer cracking and spalling of the plaster. It happens because of proprietary gypsum-based products in the mix. Under moist conditions, the sulphate from the gypsum reacts with the Portland cement paste and develops compounds of increased volume which mess up the plaster.

Just eliminate and substitute the plaster to get rid of expansion-induced disruption because of gypsum in the mix.

6. Popping: Pop-outs stand for conical fragments that appear on the plaster surface. These happen because of pollutant particles in the mix, which, when react with the moisture in the mix, extend and produce cavities in the plaster.

As soon as the reason for the pop-out is eliminated, the hole is filled with a proprietary filler and painted over.

Article Source: www.buildinganddecor.co.za

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Published By
Rajib Dey
www.constructioncost.co
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