Everything in life is a trade-off. Even cleaning the shingles on your roof has its own trade-offs. You’ll never be able to make the old shingles match the color of the new ones entirely, even if they are the same style and color. Every batch of shingles is slightly different.
Each run of shingles is coded, and the code number is printed on its wrapper. A run refers to each time the cutting machine is stopped. There can be slight differences in the size of shingles from one run to another, and there can be a slight difference in color. It is best to try to get all the shingles for a job from a single run to maintain uniformity.
The major cause of discoloration on shingles in more humid regions is mildew and fungi. The most practical material that I am aware of for removing the stains of mildew and fungi is chlorine bleach. There are mildew treatments available on the market, but the main ingredient of these products is usually a chlorine bleach of some sort.
The trade-off comes in the fact that whatever you spray a bleach product on is going to be affected in some way. The effect is customarily a reduction in the life of the material that it is sprayed on. Chlorine bleach needs the sun’s light to work its magic on mildew. Sunlight is also one of the main contributors to the destruction of fiberglass asphalt shingles. You can reduce the consequences of using a chlorine bleach on the roof by washing it completely after it has acted on the mildew.
To remove the stains, mix a 1:3 ratio of chlorine bleach to water and spray it on your roof. Make sure you do this on a sunny day. After a very short time in the sun, you will see the mildew begin to fade.
Leave the mixture on for a few hours and then rinse it thoroughly with water. The water will dilute the chlorine and render it harmless before it is washed to the ground. If there are some stubborn areas, you may need to repeat the process.
I recommend a simple cheap bleach that can be bought in any grocery store. There is nothing gained in spending a lot of money on expensive products. This treatment, if done every time you see the mildew taking hold, should take care of your stains. As I said before, mildew is a very persistent problem. It is very unlikely that you can completely prevent the recurrence of mildew, so cleaning is probably the most cost-effective.
Even if you have mildew problems on metal roofing, the treatment I mentioned above works well. I have used pressure washers, and they don’t always get all the spores out of cracks and crevices in the joints.
Treating first with the bleach and then pressure spraying does a great job of removing dirt and mildew. Remember, never use a pressure washing unit on fiberglass asphalt shingles. You will remove all the grit from the shingle and greatly reduce its useful life.
