Stain Block Damp Seal - 250ml Permanently Covers Household Stains & Damp Apply direct to damp surfaces Touch dry in 2 hours Decorate over in 4 hours Thompsons One Coat Damp Seal is a high performance interior seal developed to form a breathable, obliterating membrane that seals and permanently stops the reappearance of damp, water and other household stains. Suitable for application to both dry and damp walls and ceilings the micro-porous formulation allows trapped moisture to evaporate to prevent paint flaking or wallpaper peeling off.