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Posted: Tue Sep 25, 2007 5:28 pm
by chris_h
I need to replace a few broken concrete blocks (slightly smaller than brick size) on the top of a wall. Can anyone please tell me what ratio of cement to sand to aggregate (or whatever) I should use for the mix?
Posted: Tue Sep 25, 2007 8:46 pm
by lutonlagerlout
wouldnt it be easier just buying some blocks mate?
LLL
Posted: Tue Sep 25, 2007 10:09 pm
by Tony McC
Do you remember those screen blocks moulds you could buy from glossy ads in the sunday papers during the 1970s? The number of flimsy, fragile walls they resulted in! I don't think any of them lasted more than about 3 winters.
Posted: Wed Sep 26, 2007 2:08 am
by matt h
same as those crazy paving forms... looked ok for a while, then just disintegrated
Posted: Wed Sep 26, 2007 8:31 pm
by lutonlagerlout
Tony McC wrote:Do you remember those screen blocks moulds you could buy from glossy ads in the sunday papers during the 1970s? The number of flimsy, fragile walls they resulted in! I don't think any of them lasted more than about 3 winters.
i found some in the shed of my old house and tried to make some
just didnt work at all,as soon as i tipped them out of the mould they crumbled
LLL 
Posted: Thu Sep 27, 2007 7:54 am
by Ted
The makers of my block machine - www.dme.co.za - advocate an intital mix of 1 part cement to 8 parts river sand (coarse sharp).
However if you want to increase the mPa of the blocks you are making you can increase the cement content, introduce larger aggregate such as 10mm pea shingle and incorporate a water reducer.
Posted: Thu Sep 27, 2007 12:09 pm
by Tony McC
8:1? That's seems weak. What would that generate? Around 12-15 Newtons? I would have expected more for a walling block.
Posted: Thu Sep 27, 2007 1:08 pm
by Ted
It is to keep costs down!
African building standards are not quite on a par with European ones.
I would advocate at least a 6:1 mix though.
Posted: Thu Sep 27, 2007 4:31 pm
by Ted
Posted: Fri Sep 28, 2007 12:04 am
by matt h
hate to be there in monsoon 