A cheap floor slab could cost you in the long run

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Building foundation walls precedes the completion of the ground floor slab. Concrete is the most commonly used material in our country, but there are a number of alternatives.

Architect Abdu-Wahab Nyanzi says it is important for a developer to get a technical person like an architect for a good job; “Masons claim to know what to do, but often fall short of good practice.”

He also says another danger is that they always try to offer the client “cost-cutting” advice, which ends up being costly in the future.

“Do not allow masons to redesign your multimillion-dollar project or house. All advice on changes, adjustments, and improvements should be from or through the architect. That is the only way you can guarantee value for money,” he advises.

According to Nyanzi, it is best practice to backfill the foundations with high-quality murrum compacted well before pouring the slab.

Make sure to properly ram and compact the fill in the trenches every 150mm. Watering the murrum during compaction gives better results. Nyanzi cautions builders who want to fill up the entire area in one go to save time.

This practice should be avoided because the large volume of the earth makes compaction difficult. This can cause the floor to collapse as the earth under it starts to settle later. Nyanzi advises pouring the hardcore over the compacted earth or murrum once it reaches the required level.

The hardcore is intended to help reduce the capillarity of water and moisture through the floor. It also helps fill up soft pockets in the compacted earth and gives the floor strength. Once laid, use a sledgehammer to break down the hardcore into smaller rocks.

“To protect the floor from water and dust, we have to put a Dump Roof Membrane over the blinding before casting the concrete floor. The most commonly used material is polythene,” Nsereko explains.

Ensure that you lay the polythene sheets in overlaps. Nyanzi recommends stretching the polythene sheets beyond the foundation walls. This reduces the risk of water entering the joints of the walls and concrete. With the polythene sheets laid, we are ready to pour the floor slab.

It is good practice to put some reinforcement in the form of a mesh (BRC). The reinforcement helps protect the slab from cracking and keeps it working as a unit.