Cavity wall below french doors

[Richard Grice]

Hi all. I am currently doing my kitchen and we are installing new french doors onto the outer wall. I am wanting to tile upto the french doors so ideally need to fill the cavity up with concrete. I have heard that I should not do this so looking for advice. Thanks in advance

 

[bobasd]

there's lots of recent & detailed advice and pics on here if you use the search button.