Looking to lay a new patio. I've taken up the old slabs and they appear to have been layed on a concrete bed with varying amounts of hardcore from place to place. It looks like it's at least 10cm thick, maybe around 12cm. Under one of the flags some water got in and there is a bit of a hole now a few cm deep, but that's the only damage I can see. Can a lay a full mortar bed on to this concrete base? I'm also going to be extending the patio area so I'm going to have to dig a small section anyway and put some MOT-1 into that. So my second question would be if I did keep the old concrete bed is it fine to do the extension with the hardcore and get it to meet the old concrete base?