Question? I had new asphalt roof shingles installed approximately 3 years ago. I am starting to notice a dark discoloration that seems to be spreading. I never had this problem with my old roof shingles and there no trees which over hang the roof. Do you have any idea what this could be? And if so can it be removed without damage to the roof?
Answer— You have been invaded by Gloeocapsa magma, a very hardy algae. The streaks and discoloration is an accumulation of the algae's dead, dark-colored cells. While this algae can grow just about anywhere in the continental U.S.A., it prefers humid environments. The algae was probably deposited on your roof by wind and/or wildlife.
The new fiberglass shingles are quite different from your old shingles because they contain ground limestone, used as a filler to increase the weight of the shingles.
The algae probably invaded your last roof as well, but it starved to death because it had different materials; Gloeocapsa magma loves to eat limestone.
Introducing copper or zinc can prevent this algae. These metals are a very effective poison. Because your roof is still quite new, you'll need to install some copper strips as high as possible on your roof. Rain will wash down small amounts of copper to poison the algae. Consider installing long, 7-inch-wide strips of copper underneath the last full course of shingles at the top of your roof. You should be able to slide the copper up under the shingles approximately 5 inches or so. This will leave approximately 2 inches exposed to the weather. This can be effective as a preventative measure but will not remove heavy staining.
If you are getting ready to install new shingles, you need not do this. Many fiberglass shingles are available with colored granules that contain copper. There are enough granules present on each shingle to kill the algae. The copper is slowly released over time. Many of these shingles are guaranteed to kill the algae for the life of the shingle.
Removal of staining and discoloration can be attempted with a variety of cleaners. Most contain either sodium hydroxide or sodium hypochlorite (bleach) as their active ingredient. Be careful of the runoff as strong non diluted solutions of either may damage landscaping.
Question? I recently purchased a home with hardboard siding. The siding is in good shape but I’ve noticed some splotchy dark discoloration in areas. Do you have any idea what it is?
Answer— A possible cause of discoloration on painted hardboard siding could be "wax bleed." Wax or petrolatum is used in the manufacture of hardboard siding to make it moisture resistant. Wax can migrate to the surface. Once on the surface, wax can change the appearance of a coating by its "wetting" effect or its tendency to increase dirt retention. Contributing factors include:
- Dark paints exhibit discoloration more readily due to a tendency to absorb heat.
- Areas lacking adequate coats are more likely to stain. This appears as irregular discoloration on brushed or rolled surfaces where wax bleeding occurs in valleys or thin areas in the application pattern.
- Paints containing low levels of binder are more porous and are more likely to allow wax migration from hardboard.
- Exposures subjected to direct sun and heat will accelerate wax bleed.
In order to correct a situation where discoloration exists, one must first identify the problem as wax bleed. Do the following:
- Place a few drops of household bleach on the discolored area. If there is no whitening or bleaching on the surface, the stain is probably wax.
- Place water droplets on both normal and discolored areas. If the water beads up and runs off, a wax film is likely.
Areas of discoloration should be cleaned with a detergent solution if the surface wax is light. In severe cases, surface must be thoroughly cleaned by wiping with rags wet with a solvent such as mineral spirits. The rags should be changed frequently and the surface allowed to dry before painting.
