Cause The problem appears as a splotchy dirt collection. This discoloration can resemble mildew growth, yet will not change color when washed with household bleach. This problem is not the fault of the paint film.The non-uniform color is dirt collection that adheres to a component in the hardboard siding. This material migrates to the surface of paints, altering the appearance in a detrimental manner. This foreign material has been identified as a hydrocarbon wax.
Solution New siding: New siding: In severe cases, wax can be felt with the fingers as an oily or waxy substance. Apply a few drops of water to the board surface. If the water beads up and runs off the board, a wax condition is indicated and must be removed.Repaint old siding: The discoloration can be identified by applying household bleach to rule out possible mildew, tannin or sulfide staining. Bleaching will occur if these conditions are present. The presence of wax will not be affected by bleach. Follow above directions by applying a few drops of water to establish the presence of wax. In extreme cases of wax buildup, a clean cloth saturated with mineral spirits or VM & P naphtha solvent should be used to remove the deposits. Both rags and VM & P naphtha solvent should be changed frequently. An alternate method is to mix one gallon of water with one cup of TSP Substitute and scrub the entire surface with a scrub brush or high-pressure water wash. Rinse thoroughly with plain water. Rescrub areas where water continues to bead up on the surface to ensure that wax deposits are removed. Allow surface to dry thoroughly before applying new coating.
