Ronseal One Coat Damp Seal White 4 x 250 ml. Permanently blocks damp stains on walls and ceilings, even on damp surfaces. Quick dry: touch in 2 hrs; ready to paint or wallpaper in 4 hrs. Interior/exterior use on brick, concrete, walls. Pack of 4 for great value. Fast-drying, mould resistant, low odour.
eBay