3.1 Microbial growth is a major cause of discoloration and deterioration of paint films. This guide describes techniques used to distinguish fungi and algae from other surface contaminants.

3.2 Repainting a surface contaminated with fungi or algae generally causes more rapid infestation of the new paint than repainting a surface from which fungal or algal growth has been removed. In addition, poor adhesion, staining/bleeding, and many other problems may result. This guide describes methods for removing fungal or algal growth prior to repainting.

Note 1: It is extremely important that all steps and notes be read and followed. In particular the washing steps outlined in 5.2.2 and 5.2.4 must be fully carried out, since residual sodium hypochlorite (bleach) can cause many of the same problems, or even loss of coloration after repainting, and residual phosphate detergents can encourage further fungal and algal growth.

Note 2: This procedure is intended for use when recoating the surface. Reports of using this procedure to remove fungi and algae without recoating necessitate inclusion of a warning about the adverse effects of bleach on a coating film. The oxidative effects of bleach can degrade film properties, including particularly the "bleaching" (loss of color) in films containing organic coloring pigments (such as quinacridones, etc.), loss of gloss, chalking, etc. A small patch must be tested prior to use of this procedure for that purpose.