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Length of time on a roof for SH to become ineffective?

RCIA Founder

pat konen wrote:

I tried to search this without any luck ..... can anyone pass on their experience?

Scenario: You spray a roof with SH (between 4 to 6%) -- not overdoing it so there is not much run off from the roof -- minimal rinsing of plants is required. You are done spraying SH and do not rinse the roof. Shortly after you leave the job, it rains .... just enough to rinse the SH off the roof but not enough to thouroughly douse the plants.

Will the plants be effected? How long after the roof cleaning will SH not harm the plants in the case above?

Yes, you must warn customers about a LIGHT rain!
A good compromise is this.
Clean the roof, then let the solution SIT for 1/2 hour or more.
Go eat, pass out flyers, etc.
Then, come back, and from the ground, rinse 1/3 of the roof, water good until it stops dripping, and flood the rinsed areas until water stands.
You can rinse the whole roof, but to do so Properly will require as much time, or more, then the cleaning, and still you run a risk of active chemical damage no matter how well you rinse!
The roof cleaning solution evaporates, leaving salt behind.
Salt can brown and yellow plants, doing a 1/3 rinse will prevent 90 percent of it.

Guest

Thanks!

Guest

Great answer to a question that I also had. I worry a whole bunch about damage to plants and property. I don't want to mess with claims against my business and a bad reputation for roof cleaners in general!

RCIA Founder

gliderflier wrote:

Great answer to a question that I also had. I worry a whole bunch about damage to plants and property. I don't want to mess with claims against my business and a bad reputation for roof cleaners in general!

Always be honest with your customer.
We tell them everything in life is a compromise, and offer to pressure wash their roof, to be "Certain" there is no plant damage, but neither will the plant on their roof be killed either.
Customers usually say "A possible spot or 2 on a plant is a small price to pay for proper cleaning of my roof"

InterestedParty · Guest

This question cannot be answered with certainty. You should appreciate that sodium hypochlorite solutions are only stable at around 12-13% in water with sodium hydroxide. Try to concentrate it more than that (say, by evaporation on the roof) and it will decompose rapidly to that concentration. The rate at which the active chlorine is decomposed or used is also affected by sunlight, temperature, oxidizable soils and organic compounds, transition metal compounds and pH. So the rate at which the active chlorine (or hypochlorite) is diminished with time depends on a lot of factors.

Sodium hypochlorite is manufactured by bubbling chlorine gas through a solution of sodium hydroxide solution and much of the sodium hydroxide remains behind in the concentrate you purchase from your wholesaler. I am not a trained roof cleaning contractor and I haven't yet treated even a single roof, but I would think you should rinse all of the cleaning solution off of the roof before you leave. The residual caustic can cause severe damage to the shingles as well as any plants under the conditions you describe.

RCIA Founder

InterestedParty wrote:

This question cannot be answered with certainty. You should appreciate that sodium hypochlorite solutions are only stable at around 12-13% in water with sodium hydroxide. Try to concentrate it more than that (say, by evaporation on the roof) and it will decompose rapidly to that concentration. The rate at which the active chlorine is decomposed or used is also affected by sunlight, temperature, oxidizable soils and organic compounds, transition metal compounds and pH. So the rate at which the active chlorine (or hypochlorite) is diminished with time depends on a lot of factors.

Sodium hypochlorite is manufactured by bubbling chlorine gas through a solution of sodium hydroxide solution and much of the sodium hydroxide remains behind in the concentrate you purchase from your wholesaler. I am not a trained roof cleaning contractor and I haven't yet treated even a single roof, but I would think you should rinse all of the cleaning solution off of the roof before you leave. The residual caustic can cause severe damage to the shingles as well as any plants under the conditions you describe.

The amount of sodium hydroxide is from .5 to 1.3 percent in Sodium Hypochlorite.
I have actually collected run off from a roof cleaning, and tried to "re cycle it".
It is so weakened by it;s battle with the roof algae, it did not do much, if anything.
What is left behind on a roof, after cleaning, is basically Salt.
Now, Salt can and will damage plants, just dump a bag of rock salt on a bush, see what happens!
I have been trying for years to get Calcium Hypochlorite to work for cleaning roofs.
All that is left when it evaporates is harmless Calcium, vs Salt!

Rinsing 1/4 of the roof nearest the plant drip edges has proven to be a workable solution to the problem.

Yes, you CAN completely rinse the roof after cleaning, just allow 1/2 hour dwell time to be certain ALL algae spores are killed.
IF completely rinsing, you must be careful!
Rinse one side at a time, and do 1/2 of that side, water plants until water stannds, them, go bak and rins the rest of that side, and repeat

garyw · Feb 2, 2010

Interested party wrote;
I am not a trained roof cleaning contractor and I haven't yet treated even a single roof, but I would think you should rinse all of the cleaning solution off of the roof before you leave. The residual caustic can cause severe damage to the shingles as well as any plants under the conditions you describe.

You do have professional documentation on this statement don't you?
I would be very interested in seeing it. Could you please post it since nothing to that effect is mentioned in the ARMA statement concerning the proper way to clean a roof.

Guest

gliderflier wrote:

Great answer to a question that I also had. I worry a whole bunch about damage to plants and property. I don't want to mess with claims against my business and a bad reputation for roof cleaners in general!

I agree completely. I rinse plants thoroughly.... yet on one or 2 instances, I have still experienced some plants being effected. I'm trying to figure out some things that could have caused it.

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