anyone have any idea how to fix this? I had a plumber chip it away cause of an old tap that burst and replaced the pipe inside and tap. Attached are photos for reference. Would it be OK to just use brick mortar to fix this?
Brick mortar would be fine. I would start by drying the area and cleaning it up. Be sure there are no leaks, It needs to stay dry otherwise you will have mold and other problems. You may have to place something in the back of the hole to keep the brick mortar from falling down the back side. Then fill the hole with fresh brick mortar and trowel the surface smooth. If you do not have anything else to patch you can get one of the already made brick mortar from your favorite box store.