The invention relates to a coating material for protection against microorganism invasion on surfaces which are exposed to the effects of damp or water. The coating material has either a pH-value of at least 11.0 or is provide with a base material for the coating whereby the pH-value is at least 11. The coating material is characterized in that it contains a biocide which bonds to solid particles in a carrier material and is released in a delayed manner therefrom.