CHB Strength and cement ratio

[Mike J]

43 minutes ago, Snowy79 said:

I watched one labourer shaping the blocks to fit with his bare hands. Literally karate chopping them to the size to fit a hole. I was cringing as it was a tall property and no lintels above the windows, just a thin wooden plank holding the blocks in place until they set. I think the window was going to be the lintel. 

I have seen them build the wall, then chop out a hole for windows after the mortar sets.  No lintel at all. 

[Tommy T.]

My understanding from L is that if you want true "Class A," hollow blocks, then you buy from the factory or a dealer for the factory where they manufacture them properly, similar to USA. That is, they fabricate the blocks using whatever the proper ratio is, compress them, then kiln dry them to set them. Apparently, many hollow blocks are made with molasses as part of the mix because that supposedly makes them harder and more durable.

I have seen and, unfortunately, bought some of the cheap-o hollow blocks. They started to try to use them on our home construction and they were rubbish. They were making the cement mix, pouring it into forms, compacting them a little by hand, then lifting the forms carefully so they wouldn't collapse under their own weight. I could easily break them apart with my hands. After we squawked, they brought in a compacting machine to at least compress them. But I am sure they would not meet "Class A," quality.

As @Mike J said before:  "Here they are used more like a form to hold the concrete and rebar which provides the strength in a wall.   So strength of the block is not as important."

Edited November 11 by Tommy T.