Why mould keeps coming back after you clean it
Mould that returns in the same place is not a cleaning failure. It is a message. Something is keeping that spot wetter than the rest of the room, and until that is found, every bottle of spray buys a few weeks.
Learn to read the pattern
Where it returns tells you most of what you need.
In the corners of an outside wall, behind furniture, around the frame of a window, worst in winter and worst in the morning: that is a cold-surface problem. The air is carrying more moisture than the coldest parts of the room can hold.
In one defined patch with a clear edge, present all year, sometimes with a brown tide mark at its boundary: water is arriving there. A gutter overflowing outside, a flashing past its life, a pipe in the floor void above.
In a band along the bottom of a wall, two or three feet up, with the plaster blown behind it: that is moisture coming up through the structure, and it has usually been doing so for years.
The part a spray cannot reach
Surface cleaning removes what you can see. On plaster, in grout and in plasterboard, the growth has gone into the material, and what is on the surface is the visible fraction of it.
Where that matters is scale. A patch the size of a hand in a bathroom is a bathroom job. Growth across a square metre or more, or any growth on plasterboard that has been wet, is past the point where cleaning and repainting achieves anything, because the board itself is now the food source. At that stage a damp and mould survey in Cincinnati, or wherever you are, is the sensible next call: the survey finds the moisture source and measures what the walls actually hold, which is the thing a homeowner cannot do by eye.
Do the cheap tests first
Before anyone is called, spend a fortnight gathering evidence. It costs almost nothing and makes any later conversation far shorter.
Buy a hygrometer and put it in the affected room. Sustained readings above about sixty-five per cent relative humidity point at ventilation and moisture production. Readings that sit normal while one patch stays wet point at ingress.
Tape a square of kitchen foil tightly to the suspect patch and leave it a couple of days. Moisture on the room side means the air is depositing it. Moisture trapped behind, against the wall, means it is coming through.
Go outside with a torch during heavy rain and watch what the gutters and the ground do. A surprising share of recurring indoor damp is a blocked downpipe behaving badly for ten minutes a week.
What to fix and in what order
Source first, fabric second, decoration last. Clean, repaint and reseal only once the readings have been normal for a few weeks.
Reversing that order is the actual reason mould comes back, and it is the most common sequence in houses where it has become an annual chore.