Chemical percentage

Hi. I am new to this forum. I’d like some advice please. I am only going to be pressure washing my personal home roof. It is approximately 3000sq ft of flat white tile. I have always only used pressure but would like to use some SH for the first time.

My machine is 4400psi / 4gpm. The manual says that the chemical pickup on the machine will put down 1 gallon of chemical for every 10 gallons of water. I’m not sure if my calculation is correct but this is what I’m wondering.

If I fill a 5 gallon bucket with 12% SH, my machine would be putting down 50 gallons of water to use up the solution. That is 1.2% bleach actually reaching the tiles, correct?

If so, is that typically a good strength for removing moderate to heavy dirt/fungus/algae from white concrete tiles?

Thanks, CJW

You’re likely going to need to be between 3-5% depending on level of grime. Also, be aware that any cracks in those tiles will soak in the SH and can cause some white lines where the crack is if not thoroughly rinsed. You’re honestly better off hiring a professional.

Post pictures of your roof

Not at home right now but it looks almost exactly like this.

You won’t be able to get a strong enough solution through your pressure washer. Either buy a 12v diaphragm pump (search here to find out how) or just use a 2 gallon pump up sprayer. 1/3 SH and 2/3 water with some roof snot ( or cling on (

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That’s what I thought. You are the first one to confirm it for me. Thank you very much.

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