In Wisconsin, I plan to continue cleaning for 2-3 more weeks solid, after that I will just have to pick my days, and days might be shorter. Ideally, the surface you are cleaning should be 50 degrees, but it will work OK in the 40's. With the sun on the roof, you should be fine. I try to get all my roofs done while it is still relatively warm, leaving siding and other surfaces for when it's cooler.
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Chad A. Eneix, President, Water Dragon Inc. chad@waterdragoncleaning.com
I believe once you get into the 35 - 40 degree range for the mix or surface you are spraying, the SH will start to lose efficacy. You may want to add a little pixie dust or bump up the strength a little. The SH will take longer to react to the contaminants at lower temps, and SH likes to oxidize more than sanitize, so the pixie dust will assist the SH by helping the oxidizing part of SH, allowing for your normal batch of SH to do more sanitizing/bleaching.