Question 1

How many bags of concrete do I need for a 10 m² slab?

Accepted Answer

For a 10 m² slab at 100 mm depth, you need 1.0 m³ of concrete plus 10% waste = 1.1 m³. Using 40 kg bags (0.030 m³ each), that is 37 bags. For large pours over 1 m³, ready-mix concrete is usually more economical.

Question 2

How thick should a concrete slab be?

Accepted Answer

Use 50 mm for floor screed over insulation, 100 mm for standard garden slabs and shed bases, 150 mm for driveways with regular car traffic, and 200 mm for heavy vehicles or workshop floors. Always use a suitable sub-base of compacted hardcore beneath any slab.

Question 3

How much does a 40 kg bag of concrete cover?

Accepted Answer

A 40 kg bag of ready-mix concrete covers approximately 0.030 m³ (30 litres). For a 100 mm deep slab this covers about 0.30 m². For a 50 mm screed it covers about 0.60 m². Check your specific product label as coverage varies by mix.

Question 4

When should I use ready-mix instead of bags?

Accepted Answer

For pours over 1 m³ (roughly 33 bags), ready-mix concrete delivered by truck is usually more economical and saves significant mixing time. A standard ready-mix truck minimum order is typically 4–6 m³. For small jobs under 1 m³, bagged concrete is more practical.

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