Hi all, first time here. I have a back entrance porch which I am going to seal off, raise the floor level level with the two rooms which come off it and re-line etc. to make more kitchen space. The concrete floor slopes down from the sides like coving everywhere but under the outside door, where it is just flat and as there is no doorstep has always let wind and water in. I want to concrete up this bit to make the outside concrete foundation continuous. Will new concrete "stick" to the old? Or will water get in at the joins? My nephew is going to build up the floor with timber and wooden overlay, but I want the outside concrete bit watertight. I would welcome advice.