Slabs make structures strong. Without the slab, any structure under construction can easily collapse.

According to Herbert Muwonge, a construction engineer, the components required for the construction of a slab are wire mesh, hardcore  (the infill of materials such as broken bricks, stone, or concrete, which are hard and do not readily absorb water or deteriorate) and iron bars, are all needed to hold the slab together.

“One also needs polythene, because it helps to stop water from moving from underground to the upper level of the structure. It is an expensive venture,” he explains. Abdu-Wahab Nyanzi, an architect with JR Consultants, says there are ground and upper slabs. For example, suspended slabs are used to create upper floors. In such cases, the suspended slab is unavoidable.

Types

Solid concrete

Nyanzi says solid slabs are commonly made from concrete. This type is probably the most expensive, but the strongest. The slab is made of concrete and reinforcement in the form of steel.

Semi-solid slabs

Nyanzi says this type is commonly used in residential houses. It is cheaper and gives the required strength for the building to stand. It is made of concrete, reinforcement, and hollow fill. The fill used most commonly is max-pan, but hollow concrete blocks are also an option.

Concrete slab

Timber slabs

“Well-seasoned timber is formed into a structurally sound frame to support live and dead loads. Expertise and care are necessary when working with this kind of slab because it is prone to pests and is vulnerable to fire. As a minimum, the timber should be well seasoned and treated with an approved preservative”, Nyanzi explains.

Composite slab

This is a combination slab that is made from a steel or timber framework, covered with steel or timber and finished with a thin reinforced concrete mix not exceeding 75mm.  Nyanzi says this slab is probably the most economical and the least used in Uganda. “Some experts put the possible saving at about 40% of what one would spend on the semi-solid slab,” Nyanzi says.

What can cause bad work and cracks?

Muwonge says poor mixing of building materials, like cement sand and aggregate will cause cracks in slabs. Normally, poor workmanship is as a result of ignorance, carelessness, negligence, lack of proper supervision or worse still, a combination of all issues. Selecting a slab type should be guided by an architect to ensure that its function is synchronized with the architectural qualities which the design is trying to achieve.