hickeys45 wrote:

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Tried an experiment today on a small section of fungus covered cement fibre slate. First I tried a degreaser on some and it didn't do anything. Next I tried SH mixed with the degreaser and again poor results. Then I poured SH straight from the drum (12.5 supposedly) on a few slate and the result was dissapointing to say the least. While it did seem to soften it up, the black run off that I was expecting didn't happen. I am starting to think that I will never get a mix to work on slate when the temperature is low. Any ideas would be greatly appreciated.

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 What was the temp, in farenheit ?

The cold slows the reaction down. I have seen it take nearly an hour to work before, so did u wait long enough, and was your stuff fresh and potent, or merely salt water ?

hickeys45 wrote:

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Thanks Eric and Chris. The temperature was roughly 28/30F. No I didn't wait more than a couple of minutes as I have had problems before with Fibre Cement Slate. on two occasions when I left the SH mix (30/70) on or kept retreating, white fibers were washed out from under the slate and I found it hard to wash them off the roof. Eric is it preferable to keep the roof moist to keep the mix working. I buy the SH in 25ltr drums from a Farm supply store where they sell a lot of it so it should be fairly fresh, also when I use it on driveways etc it seems to work just fine.

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 The roof cleaning chemical always takes time to work, especially when it is cold.

Here is a slate roof cleaning video I threw together some time ago, out of pictures.

It came out great, except the copper dormer got hit with the chemical, and it made it all shiny!

Lucky for us, the customer likes the shiny copper, because we stripped his patina off.