Damp wall behind tiles in bathroom..dehumidifier time?

[Edewakefield]

Hi folks,
Many thanks in advance for any advice anyone can give.

My little dilemma is that I believe I have damp in the bathroom walls behind the tiles. I thought I had dried out the walls sufficiently before tiling the bathroom.
I have concluded that using a dehumidifier would get the damp out and then I could treat the mould that has appeared in the grout. This has shown very badly in the bottom 18 inches of the shower tray in the shower end of that bathroom.The bathroom is a single story air cavity extension. Nine foot by five foot.
My questions are

a. What size dehumidifier would you recommend to get the damp out of the walls? As powerful as possible? 10 litre or much bigger?

b. What type of grout would you recommend to re grout affected parts of the shower? I have used bal on the floor tiles which seems better than the wall grout.

Many thanks,

Ede

[chris_on_tour2002]

what in particular makes you think that the damp is behind the tiles? could it just be a build up of mildew on the tiles from showering? do you have adequate ventilation in the room?

and my choice of grout would be BAL micro ban. contains anti fungal and anti bacterial agents to inhibit mould growth and yellowing.