The honest numbers
For a 9 inch hollow block made at a sensible 1:8 mix, expect about 30 blocks per bag. For 6 inch blocks, about 40. Yards claiming 50 or more 9 inch blocks per bag are using far too little cement.
Why weak blocks cost more
A weak block breaks in handling, cracks under a lintel and soaks up plaster. You lose more in breakage and extra plaster than you saved on the block price.
A cheap block that breaks is the most expensive block on site.
Test before you buy
Drop test: a cured block dropped from waist height onto firm ground should not break. Scratch test: a nail should not easily scratch the face. For bigger jobs, send six blocks to our laboratory for a crush test.
Curing blocks
Blocks need seven days of wetting under shade before sale. Fresh blocks sold the next day look fine and fail later.
Written for this demo. Always follow your engineer's instructions.