Cavity fill advice

[daz0987]

Hi all,

I’m self building a small extension. The trenches are dug and concrete footing poured. I’m building the inner and outer skins using 100mm concrete blocks with a 100mm cavity.

Rather than mix concrete to fill the cavity, can I fill the cavity with concrete blocks and mortar?

Thanks in advance

 

[noseall]

Rather than mix concrete to fill the cavity, can I fill the cavity with concrete blocks and mortar?

Yes, but why?
It will be more difficult (keeping everything upright and in-line) and how will you achieve the chamfer towards the outer course?

 

[daz0987]

I thought it might be quicker and easier if I could build both skins then drop the blocks in between and put some not too wet mortar on top chamfered to the outside. There is also a drain that I am having to bridge and I thought it would be a good way of avoiding filling that space?

 

[^woody^]

You're not tying the skins together then?

 

[daz0987]

I didn’t think they needed tying below dpc? The space I’m talking about filling is really just the space below finished ground level to prevent the skins collapsing in. Should I be using ties there also?

 

[^woody^]

Any cavity wall above or below ground needs to be tied max 450 vertical and 900 horizontal staggered pattern. That can still come apart, and ties also transfer loads between the leafs.

You should have built a solid wall in the ground if filling the cavity with blocks was your plan