We recently moved into a 1970s house during mid winter, it has an extension with a concrete slab adjoining the existing home with a subfloor.
I have recently noticed a wet area to where the extension meets the existing house (see photos below). There is a split system and a hot water heating system on the corner of the house. There was some condensation from the split system running directly onto the wall but since having it off for the last 2 weeks, the water patch on the wall has not change.
The mortar is becoming very sandy between some of the lower bricks.
Any thoughts on what could be causing this?
Thanks in advance!