Concrete or Mortar

[Munroast]

I an building a small retaining wall in the garden from 8" hollow blocks. I was going to fill them to lock them together. Usually I believe they are filled with concrete - As it happens I have a load of sharp sand, would there be much disadvantage if I just filled the blocks with a 4:1 sharp sand cement mix, or would it be a better job if I bought some gravel or an aggregate mix and filled with concrete?

Basically would a 4:1 sharp sand mix be as strong as a 4:2:1 agg mix ?

 

[noseall]

Filling them with sharp sand mortar would be better than not filling them at all but would not be as strong as using concrete.

It would be even better to insert rebar and fill with concrete, but this may be OTT.

What sort of retaining work is this wall doing? Are you addressing all the design factors?

It's as much about protecting the wall from sulphate attack via the soil and preventing water build-up etc, as it is about the strength of the wall itself.

 

[tony1851]

The 1:4 sand,OPC mix will shrink more than the concrete mix; personally I'd go with the latter. It's not just a case of relative 'strength', but how the materials work together.

 

[loply]

Why not go with a compromise and mix your sand with some ballast, for a sandy-ballast mix. Will mean you need to buy less ballast and can use up your sand.