Discoloration

Discoloration

When slight dirt accumulates owing to repeated soiling, Discoloration of paint occurs. Following this, a flattening stage develops when the coating starts to chalk, gradually and erode away. Paint on the surface is sometimes discolored by mildew, blue stain, wood extractives and metals long before repainting is necessary.

Possible Causes

Solutions

Mildew
The most common cause.
• Ensure mildew is killed, before repainting.
• Use a bristle brush to scrub the painted surface with a mix of 1/3 cup household detergent, 1 quart (5%) sodium hypochlorite (household bleach) and 3 quarts warm water.
• This solution kills mildew and cleans the area.
• Rinse the area to be repainted with fresh water, thoroughly.
Water-Soluble Extractives
The extractives dissolve and leach from the wood by water. The water moves to the paint surface, evaporates and leaves the extractives behind as reddish brown stain.
• Eliminate moisture problems to stop discoloration.
• Wash the discoloured areas using mild detergents immediately when the problem starts developing.
• Use paint cleaners if the stains are darker.

Ferrous Nails
Usage of standard ferrous nails on exterior siding and painting on them leaves a red-brown discoloration through the paint and the immediate vicinity of the nail head.
• Prevent rust stains by using high quality galvanized stainless steel and aluminium nails.
• Do not use any standard ferrous nails.
• Use an oxalic acid solution to remove the discoloration, if chemical discoloration is not already sealed beneath a finishing system.
• Apply several applications of an oxalic acid solution to the stained surface, using at least one pound of oxalic acid per gallon of water that is preferably hot.
• Wash the surface with warm and fresh water to remove oxalic acid and any traces of the chemical that causes stain.

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