Description: Staining of a paint film by diffusion of a soluble coloured substance from the underlying paint to give undersirable discoloration or staining.Often seen where bituminous or tar based product are overcoated with topcoats in which the tar or bitumen is soluble. Also occurs with emulsion paints.
Probable Causes: ‘Bleed Through’ is generally a full or partial redissolving of the previous coat or an ingredient of a previous coat and can occur when strong solvents are used in the topcoats.
Prevention: Use correct coating specification and materials. Use compatible materials. Use appropriate sealer coat if possible.
Repair: Remove stained or contaminated layer. Apply a suitable sealer coat which will prevent the diffusion of soluble coloured material from beneath. It may be possible to apply a sealer coat wihout the removal of the stained / contaminated layer.