A 50 kg bag of cement typically makes about 15 to 25 hollow 9-inch (225 mm) sandcrete blocks, depending on the cement-to-sand ratio. Commonly quoted figures are about 15 blocks at a 1:6 mix, 17 at 1:7, 20 at 1:8 and 25 at 1:9, according to Structville's guide to sandcrete blocks. Treat them as rough guides, not guarantees.
Why does the number of blocks change?
- Mix ratio. More sand per bag of cement stretches the cement further, but makes weaker blocks.
- Block size. A 6-inch block uses less material than a 9-inch block.
- Measuring. Different wheelbarrows and buckets give different real ratios.
- Water. Too much water weakens the block. A water-to-cement ratio of about 0.5 to 0.6 by weight is commonly recommended, which is roughly 24 to 30 litres per 50 kg bag.
- Compaction and curing. Poorly compacted blocks that dry too fast crack and crumble.
Should you use the leanest mix?
No. A leaner mix gives more blocks per bag but weaker blocks, and weak blocks cause problems later. Many commercial block makers in Ghana use 1:6 or richer, according to research on the Sekondi-Takoradi area. Follow the Ghana Standards for sandcrete blocks and ask your engineer for load-bearing walls.
Which cement should you use?
The Ghana Standards Authority guidance points to 42.5R for building blocks and pavement slabs. See which cement for blocks, plastering and columns.
Selling cement to block makers?
Block makers buy in volume and buy often. If you run a building materials shop near them, a steady supply matters. Read how to buy cement in bulk.
Written by Mark Nii Barnor Adom. About the author