Mortar mix for block wall

15 May 2009
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United Kingdom

I am going to build a retaining wall out of 'hollows' two blocks wide with rebar.

I will start from a concrete base, and will have to fill the hollows with concrete around the rebar.

Can I use the same concrete mix; as the base, as the joints and the fill?

Thanks James.
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Depends on what mix you are using in the base..
Should really be using a C35 mix in both reinforced base and pockets.. course it also depends on what you are retaining, a 3m high wall would need a higher spec.. etc
Hey Static,

Thanks for getting basck in touch, any chance you could answer a few direct questions?

1. What is the mix for C35, I was planning on C20?
2. What mix for mortar - or the C35?
3. The walls are 1m above ground, with rebar in every hollow can I get away with one block thick?

The two walls are gonna be retaining walls to hold up a domestic driveway.


Sorry things got busy yesturday..

1:1:5 or 1:1:6 mix for the mortar should be fine, the main strength in the wall comes from the pockets and overall weight..
At 1m high, i would have thought C20 would be fine for pockets and base..
When you say one block thick, do you mean 100mm or 215mm.. would go 215mm minimum thickness for that size wall..

Bear in mind that if the length of the wall is over about 6-7m then you should put a movement joint in or things will crack over time.
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Thanks Static asnd The Oldun,

Walls are only 3m long, but will run another 2m when I've sorted out some soil pipes - so will end up with an expansion joint.

Got a bit bogged down when I was looking at modular mortarless retaining walls and somehow forgot the basics.

Back on course now, cheers chaps.


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