Why you need to know the type of sand you are buying

By Umar Nsubuga

 

WITH so many choices of building materials and house components in the building industry today, many of us when we think of building the first consideration in choosing building materials is cost, yet we also have to know the kind of materials we use.

 

The shortage of local building materials like sand has forced prices up as dealers have started getting fake materials.

 

With sand many people are building without knowing which kind of sand they are using on their sites. 

 

Abdu-Wahab Nyanzi an architect at JR Consultants says good sand is supposed to be free of impurities like soil, clay and humus.

 

One can tell that the sand is good by picking a handful of it and rubbing it through fingers to feel its texture.

 

“Its nature should not stick together like clay. Ordinarily if the sand is dry, it should not stick when you hold it in fist and release it”, he says.

 

According to Nyanzi it is advisable for any site developer to engage experts in building materials to ascertain their quality before effecting transaction.

 

Anything can happen during the construction, use of poor quality materials, like building sand yet it plays an important role in the strength of your structure, he adds.

 

Types of sand

According to Nyanzi sand should be classified as coarse and fine for grey sand and brown sand is usually mixed with silt (mukoka).

 

Why mixing sand

The sand is mixed to give the mortar or concrete mix the structural strength it requires. Nyanzi says improper blend of aggregate influences the cement and water demand for a given concrete mix and affects workability, compact ability and cohesion characteristics of pump able concrete mix.

 

It also influences the compressive strength, flexural strength and other properties like permeability and durability of concrete.

 

Bad sand and why a structure may get cracks

Nyanzi says sand with impurities is bad. The commonest impurity is clay in it.

 

“The difference in composition clay causes cement mixes to crack and lowers performance in strength. Sometimes the sand may be good when it’s delivered on site but it is contaminated by the builders at times”, Nyanzi says.

 

Contamination comes from mixing on dirty backgrounds and using dirty water.

 

Mixes should be made on clean background like a flat steel sheet, timber board or plastered platform to avoid contamination.

 

Some sand dealers harvest the building sand from the trenches and valleys brought by running water from downpour, while others deal in ordinary brown soils, which is disguised as the lake sand.

 

Many builders have been using this for laying bricks, but it is of poor quality and not strengthens the structure. 

 

When plastering why using fine sand

Nyanzi says the choice of sand when plastering is not limited to one type. It is always good to mix the coarse and fine sand to achieve a strong mix.

 

“In cases where finer finishes are required, it is advisable to sieve the sand to remove the bigger aggregates”, he advises.

 

Buying sand

Bamu Kisekka who deals in sand says that most of the city sand mines are overdrawn forcing them to them to distant far areas like Luwero, Kapeeka, areas around lake victoria even some people are currently getting sand as far as Masaka.

 

He says site developers, who are opting for cheap building sand are compromising the quality of their buildings.

 

Costs

According to Isam Matovu who drivers ten tyre tipper truck (magulu kumi) for building sand a truck ranges between Sh450,000 and Sh600,000 around the city areas, but is dependent on the distance and the quality, while that of the plaster ranges between Sh350,000 and Sh500,000.

 

Matovu says the shortage of mining areas has forced their prices up drivers and dealers have started getting them from islands and from far areas. However, unscrupulous dealers are taking advantage of the increased demand for the sand.