So you might say "Why would I want to clean my roof? That's the way a roof is supposed to look...right?. Why "waste" the money?" Well, there a couple of reasons why it is important to clean a slate roof. The first reason is that it simply looks fresh and bright but the most important reason is Winter Weather in New England. Almost without exception, slate problems occur where snow, moss or algae has lain on the slate surface for prolonged periods. In cases where trees are not hanging over a roof, the surface is problem free (trees create a fertile environment beneath them that fosters moss, algae and lichen growth which holds moisture and snow in place). In winter as the daytime sun melts some of the snow, the water falls into the slate through fissures and cracks and absorbs into the slate. At night it freezes and expands, widening the cracks and pores, providing larger cavities for the next days melting water. The cycle continues with tremendous expansion and contraction of the slate around the cracks. A once strong and solid surface has become broken and flakey. This situation will requires expensive repair or replacement. The best way to eliminate or reduce this problem is to eliminate the algae, moss and fungus.

Important Note: Proper surface cleaning involves either physical scrubbing or some level of pressure to remove the plaque and fertile substrate. There are several enterprises out there marketing products that they claim do not require rinsing. "Spray and Forget" and other "No Rinse Roof Treatments" are good starts but do not remove the foundation which will only invite regrowth in a very short time, sometimes in only a few months. We all know that mouthwash alone doesn't make for healthy oral hygiene, and that brushing and flossing are necessary. It's no different with roofs, siding, decks, or any other surface. There is lots of documentation on this. Common sense also works.