damp under tiles

[shedi123]

Hi, I'm going to be re tiling around our shower bath tomorrow. I have just removed the old tiles that I fitted about 4 years ago. I have found that the tiles are damp underneth. I don't what this to happen when i retile so what did i do wrong and how can i avoid this happening again? (the walls are brick and plaster if that makes a difference)
Also i'm tiiling one extra bit of wall which is in the shower area that is plaster board. It is the water resistant board but is there any tips with regard to damp on tiling on plaster board?
Thanks in advance.

 

[Richard C]

Use decent trade adhesive & grout for the tiles not the cheap DIY stuff & tank the plasterboard first or you will have problems; & you should use flexible adhesive/grout on the plasterboard or it'll crack.

 

[shedi123]

How do you mean tank the plasterboard? Do you mean seal with PVA?

 

[gcol]

How do you mean tank the plasterboard?

http://www.trades-direct.co.uk/modules/shop/view.asp?Prodcode=9005-102