The easiest solution would be get a pack of cheap white ceramic tiles and tile the back of the "slot in" to the floor, and do the same with the drier
Tiling the back wall is definitely not the way to go:
1. there's excessive condensation, and possible signs of damp at lower left -
2. rising damp coming through the gypsum plaster could blow the tiles.
3. warm air hitting the tiles would cause perhaps even more condensation & mould - as in unventilated tiled bathrooms.
4. Simply fixing the tiles behind all that pipework and fixings, & making good the lower left plaster, would be a job in itself.
Yes, thats black spot condensation - providing trickle heating and ventilation 24/7 is the best way to go.
Breaking plaster contact with the floor - cut back 40mm to 50mm where possible might help a little.
You could install a 9" x 3" vent in the back of the counter or drill some holes - to have some through ventilation.
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