Ryan Cash
UAMCC Associate Member
What strength SH do I need for Roof Washing? What Strength SH do I need to Clean ________?
These are questions I hear a lot. So let’s break it down.
But first: Here is something I see Soft Wash Contractors get confused with a lot: Percentages vs Ratios.
For Example, a 1:4 mix is not the same as 1/4 (25%)…
That 1:4 mix actually means that there is 1 part chemical, and 4 parts water. That’s a total of 5 parts. So to get your percentage, you would divide 1 by 5..not by 4
So 1:4 is actually 1/5, or 20%.
So to simplify everything, first look at draw rates and how they translate to percentages:
This gets confusing for most contractors when they’re then dealing with Sodium Hypochlorite and trying to dilute it down to usable strengths. But knowing those percentages and knowing that, typically, Sodium Hypochlorite is purchased at 12.5% strength, it’s a simple math problem to find out final mix strengths based on the mix ratio.
You simply multiply 12.5 by the percentage. Example: 1:3 is the same as 25%, or 0.25.
So a 1:3 mix of 12.5% SH would leave you with a final application strength of 3.125% SH.
Here is a chart to break down the most common used SH mixes for the three common starting strengths.
Now that we know what ratios will result in which strength of mix, let’s look at what %SH is generally needed for cleaning the most common substrates. Always Remember to do a test spot when needed and to start low, increasing mix strength as needed.
Asphalt Shingle Roofs: 3% (Work up to a max of 6% as needed)
Concrete Tile Roofs: 4% (Up to 6% as needed)
Metal Roofs: 1% (Up to 3%) Many metals roofs can be damaged by SH, so test first! Rinse much more than normal too
Vinyl Siding: 1% (Up to 2%)
Stucco Siding: 23%
Concrete Pre Treatment: 1% (Up to 3% for bad growth)
Concrete Post Treatment: 3%
Wood: 1% (Presoak with water first, apply light SH, increase strength as needed)
Composite Decking: 1% (Increase up to 23% as needed)
Asphalt: 0% (Typically not used for Asphalt Cleaning)
Brick: 2% (up to 3% max)
Again, keep in mind these are guidelines, not hard rules.
Remember also that Sodium Hypochlorite is used to remove Organic staining only! Other stains such as rust, oil, soot, etc. will need specialty chemicals to remove.
These are questions I hear a lot. So let’s break it down.
But first: Here is something I see Soft Wash Contractors get confused with a lot: Percentages vs Ratios.
For Example, a 1:4 mix is not the same as 1/4 (25%)…
That 1:4 mix actually means that there is 1 part chemical, and 4 parts water. That’s a total of 5 parts. So to get your percentage, you would divide 1 by 5..not by 4
So 1:4 is actually 1/5, or 20%.
So to simplify everything, first look at draw rates and how they translate to percentages:
 1:1 – 50%
 1:2 – 33.33%
 1:3 – 25%
 1:4 – 20%
 1:5 – 16.66%
 1:6 – 14.29%
 1:7 – 12.5%
 1:8 – 11.11%
 1:9 – 10%
 1:10 – 9.09%
This gets confusing for most contractors when they’re then dealing with Sodium Hypochlorite and trying to dilute it down to usable strengths. But knowing those percentages and knowing that, typically, Sodium Hypochlorite is purchased at 12.5% strength, it’s a simple math problem to find out final mix strengths based on the mix ratio.
You simply multiply 12.5 by the percentage. Example: 1:3 is the same as 25%, or 0.25.
 0.25 x 12.5 = 3.125%.
So a 1:3 mix of 12.5% SH would leave you with a final application strength of 3.125% SH.
Here is a chart to break down the most common used SH mixes for the three common starting strengths.
12.5% SH Starting Strength
 10% SH Starting Strength
 8% SH Starting Strength
 5% SH Starting Strength

Now that we know what ratios will result in which strength of mix, let’s look at what %SH is generally needed for cleaning the most common substrates. Always Remember to do a test spot when needed and to start low, increasing mix strength as needed.
Asphalt Shingle Roofs: 3% (Work up to a max of 6% as needed)
Concrete Tile Roofs: 4% (Up to 6% as needed)
Metal Roofs: 1% (Up to 3%) Many metals roofs can be damaged by SH, so test first! Rinse much more than normal too
Vinyl Siding: 1% (Up to 2%)
Stucco Siding: 23%
Concrete Pre Treatment: 1% (Up to 3% for bad growth)
Concrete Post Treatment: 3%
Wood: 1% (Presoak with water first, apply light SH, increase strength as needed)
Composite Decking: 1% (Increase up to 23% as needed)
Asphalt: 0% (Typically not used for Asphalt Cleaning)
Brick: 2% (up to 3% max)
Again, keep in mind these are guidelines, not hard rules.
Remember also that Sodium Hypochlorite is used to remove Organic staining only! Other stains such as rust, oil, soot, etc. will need specialty chemicals to remove.
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