# Forum Home Renovation Concreting  How to add adequate footing to a 90mm slab with existing brk wall above.

## AndreReno

I have a 90mm - 100mm  slab at the back of the house (lounge room). A single leaf brick wall sits on top of the slab at the lounge/kitchen divide.
There is no adequate footing under that wall, it is just the 90-100mm slab edge. 
The other walls are the same but I will pull them down and expand out and put deep footings in for the new walls so they aren't a problem.  This is the only wall that I would prefer not to pull down as it will create a lot more work. 
I've heard that in restoration work, it is possible to insert concrete under an existing wall to provide a deep enough footing, but that it must be done in sections, at a time, so the existing slab doesn't crack as you dig out.
Does anybody have any info on this, or experience.
Methods, precautions etc. 
Also, any thoughts on issues like compaction. I can't see how it can be done mechanically, unless I rely on the existing compaction.  The slab has been down for about 30 or 40 years by the looks of it.

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## barney118

If it's been up for that long what makes you think there's a problem? Is the wall cracked? An engineer will help you understand if anything is required if anything at all.  
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## AndreReno

It is not a case of an existing problem with the slab or wall.  When I extend the room, as I said, the other walls will be pulled down, but this wall will appear on the 'existing' plan.  The wall will need the correct sized footing to conform. The plans won't get through, or past anyone as it is.
I would like to fix this issue separately, well before I start putting plans together. An engineer mentioned to me, some time ago, that he has done remedial work by inserting the footing in sections below a thin slab. Other than suggestion, I don't have much info on the methods used.

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## Gaza

Dig 600mm long miss 600mm then pour sections first dug then repeat   
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## Marc

it is called underpinning, plenty of info on the net. Basically as Gaza said.

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## AndreReno

Thanks for letting me know what the correct term is..
I had heard of this term, but mistakenly thought that this was only an injection method. I've now googled the term and can see that there is a few different methods under this name and I've now got some info on the traditional method of mass underpinning which suits me as it is basically low tech and I can do it myself with a shovel and wheel barrow.
thanks again.

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