Pressure Washing Solution

[BlufftonSC]

We're in a two-story house that needs pressure washing. Our contact wants to use a bleach solution to remove mold. He said they'll hose down the plants and then hose them down again after washing. Is that enough to protect the palms (sabal, Chinese fan, Queen, needle, etc.) near the house? Input would be greatly appreciated!

[Dypsisdean]

Bleach is chlorine, and chlorine kills. But it will depend on the contact time and concentration. So washing before and immediately after would obviously help, and probably be sufficient for the tougher palms you mentioned. And different plants will react differently as well.

Testing a leaf or two would be easy enough.

I can tell you that I dumped chlorinated pool water on Howea roots for years and it had no effect. But contact with the leaves may have been a different story.

[sarasota alex]

Not enough. It near and dear to my heart since I'm planning to take the person who pressure washed the house next to court, if he refuses to pay for the damage he caused. And it's the same story I heard from him. Please keep in mind that using chlorine does not make anything cleaner. It's used to save time and effort.

[AggiePalms]

I would be very careful about blowing spray...Chlorine is a very potent chemical that causes major damage to many tissues. For instance, chlorine bleach is used in biology labs to eat away the flesh of frogs to leave just the skeleton. I don't know the details of its chemical interactions with cell walls or cellular metabolism, but I wouldn't let the spray get on the leaves. If you must pressure wash using chlorine, maybe hold up a plastic sheet between the plants and the gun? Your plants look much too healthy to harm them.

[_Keith]

There are other products that work better, and claim to be safer on plants and people than bleach. This is one: Krud Kutter

[sonoranfans]

Bleach is sodium hypochlorite(NaOCl). In water it becomes hypochlorous acid and sodium hydroxide(HOCl+ NaOH). It is a powerful oxidizer, eg it rips molecules apart. Sodium hydroxide digests cellulose, not good. The damage will depend on contact time and strength of solution. If you pour it on plant root areas it will react rapidly with humus and microbes so it may not hurt your roots since after reaction it is relatively harmless(its reduced). It will kill microbes, so the beneficial ones will die as well. It is used to kill fungus in some applications on plants, and as a sterilizer of biologics in the laboratory. I would be very careful about having NONE get in a nook or cranny on the plant. Myself, I would tell this turkey he's not allowed to spray it on my palms, and I would watch him. I'd wrap the palms up and rise them off right after he was done if he must use it around them.

[MattyB]

hahaha "Turkey". I could just hear you saying that Tom, it was great.

[palmislandRandy]

I have to have my roof cleaned every few years & I only have them use water. I can smell the bleach when a neighbor has theirs cleaned. I don't wait till it gets too bad, so plain water works fine. The damage to the palms was due to the concentrated spray from the pressure washer. The high pressure shreded the heck out of the fronds.

Randy

[PalmatierMeg]

Just reading this topic chilled my blood. Spraying bleach solution everywhere? Environmental hazard, bar none. I wouldn't want kids or pets around it so why should I want palms and landscape plants?

[Dypsisdean]

Just reading this topic chilled my blood. Spraying bleach solution everywhere? Environmental hazard, bar none. I wouldn't want kids or pets around it so why should I want palms and landscape plants?

Do you keep your kids out of swimming pools? Would splashing and spraying pool water be considered an environmental hazard?

Don't forget that bleach (chlorine) has been used for a hundred years in drinking water and in keeping swimming pools sanitary. Swimming pool water is a "bleach solution." It is like almost any chemical. Use it responsibly - meaning the proper concentrations and conditions - and it provides benefits.

Take a potted palm and dip the leaves (not the entire pot) in a swimming pool - and then immediately wash them off with fresh water. I would guess you will not see any damage. But the small concentration of chlorine in the pool water is enough to kill any algae in the pool, or mold on the side of your house (if left in contact).

The key is in the concentration, and the duration of contact.

Actually the proper procedure would be to first use a low pressure or brush/roll-on application to those surfaces in need, while avoiding plants, metals, and pets - and then pressure washing later when most if not all of any chlorine has dissipated and the molds and mildew have been killed.

[PalmatierMeg]

Guess I misunderstood. If the topic had stated the guy was spraying chlorinated pool water I would've gotten the idea.

[sonoranfans]

If this is being applied to kill mold, it is typically used in a much higher concentration than in pool water. This is because it must oxidize the mold hence it needs more hypochlorate to react. Think pool shock and algae, heavy algae. Sometimes you repeat the application of shock and cant swim until some time lapses(it reacts and the concentration drops to a low level). If you have any doubts, just ask the guy to put some of the solution in his eye, LOL! Pool water doesnt really hurt the eyes if you rinse afterward. In my experience bleach is used in MUCH higher concentration for cleaning. As to its residual toxicity, I wouldnt be too concerned as it decomposes after it reacts to oxidize. I'd say if the guy is willing to put some undiluted solution in his eye it will be quite safe for any palm. I suspect even if he can dilute it 1/2 or even 1/5 parts water and put it in his eye, it will still be safe for your palms.

Edited January 4, 2011 by sonoranfans

[PalmatierMeg]

If this is being applied to kill mold, it is typically used in a much higher concentration than in pool water. This is because it must oxidize the mold hence it needs more hypochlorate to react. Think pool shock and algae, heavy algae. Sometimes you repeat the application of shock and cant swim until some time lapses(it reacts and the concentration drops to a low level). If you have any doubts, just ask the guy to put some of the solution in his eye, LOL! Pool water doesnt really hurt the eyes if you rinse afterward. In my experience bleach is used in MUCH higher concentration for cleaning. As to its residual toxicity, I wouldnt be too concerned as it decomposes after it reacts to oxidize. I'd say if the guy is willing to put some undiluted solution in his eye it will be quite safe for any palm. I suspect even if he can dilute it 1/2 or even 1/5 parts water and put it in his eye, it will still be safe for your palms.

I like the idea of contractor putting bleach solution in his eyes first.

[Dypsisdean]

My point of using pool water as an example was to illustrate that there are probably levels of chlorine that could be used safely to kill the types of mold and algae that would grow on house siding, and still be benign if washed off plants immediately. Algae that persist on dry surfaces should be more easily killed with a wet chlorine than any of the aquatic types. So at residual pool levels of 2-4ppm the chlorine should kill the relatively small amount of mold or algae present on dry house siding, and even pass the "eye test." A still low 10 ppm is the minimum restaurant requirement for rinsing your dishes - to assure killing all microbes. Enough to make your eyes red, but not causing any damage. My point was that a very low concentration is all that would really be required.

But my guess is any contractor would be wanting to use over-kill concentrations ten times that amount, because bleach is cheap and it would save a little time - IMO not only unnecessary, but not good for the reasons we have been discussing. A simple pool chlorine tester would indicate the chlorine levels in any application.

[sonoranfans]

My point of using pool water as an example was to illustrate that there are probably levels of chlorine that could be used safely to kill the types of mold and algae that would grow on house siding, and still be benign if washed off plants immediately. Algae that persist on dry surfaces should be more easily killed with a wet chlorine than any of the aquatic types. So at residual pool levels of 2-4ppm the chlorine should kill the relatively small amount of mold or algae present on dry house siding, and even pass the "eye test." A still low 10 ppm is the minimum restaurant requirement for rinsing your dishes - to assure killing all microbes. Enough to make your eyes red, but not causing any damage. My point was that a very low concentration is all that would really be required.

But my guess is any contractor would be wanting to use over-kill concentrations ten times that amount, because bleach is cheap and it would save a little time - IMO not only unnecessary, but not good for the reasons we have been discussing. A simple pool chlorine tester would indicate the chlorine levels in any application.

Point taken that there are levels of safe chlorine, though some debate the safety of the chloromethanes produced, I do not. But I think you have underestimated the levels of hypochlorite needed to digest visible algae or mold. The hypochlorite is consumed in a stoichiometric(ratioed) reaction and there is clearly orders of magnitude(2-3?) greater mold than the ppm level on the wetted surface volume. For this reason, unless you want to rinse the surface over and over again for perhaps days, you will need more than 10x, probably 100x or more hypochlorite to remove the algae. Also because the length of time of the job is a cost factor, they will be encouraged to overdo the bleach concentration and get the job done faster. Even any pool manual tells that the ppm chlorine level is there to prevent algae appearance, not to digest visible algae. Visible algae is treated with shock, that that is thousands of times more concentrated. Finally the chlorine tester for a pool is designed to work over a narrow range that is typical of pool applications, I would not believe its accuracy for anything over 20ppm.

[Dypsisdean]

My point of using pool water as an example was to illustrate that there are probably levels of chlorine that could be used safely to kill the types of mold and algae that would grow on house siding, and still be benign if washed off plants immediately. Algae that persist on dry surfaces should be more easily killed with a wet chlorine than any of the aquatic types. So at residual pool levels of 2-4ppm the chlorine should kill the relatively small amount of mold or algae present on dry house siding, and even pass the "eye test." A still low 10 ppm is the minimum restaurant requirement for rinsing your dishes - to assure killing all microbes. Enough to make your eyes red, but not causing any damage. My point was that a very low concentration is all that would really be required.

But my guess is any contractor would be wanting to use over-kill concentrations ten times that amount, because bleach is cheap and it would save a little time - IMO not only unnecessary, but not good for the reasons we have been discussing. A simple pool chlorine tester would indicate the chlorine levels in any application.

Point taken that there are levels of safe chlorine, though some debate the safety of the chloromethanes produced, I do not. But I think you have underestimated the levels of hypochlorite needed to digest visible algae or mold. The hypochlorite is consumed in a stoichiometric(ratioed) reaction and there is clearly orders of magnitude(2-3?) greater mold than the ppm level on the wetted surface volume. For this reason, unless you want to rinse the surface over and over again for perhaps days, you will need more than 10x, probably 100x or more hypochlorite to remove the algae. Also because the length of time of the job is a cost factor, they will be encouraged to overdo the bleach concentration and get the job done faster. Even any pool manual tells that the ppm chlorine level is there to prevent algae appearance, not to digest visible algae. Visible algae is treated with shock, that that is thousands of times more concentrated. Finally the chlorine tester for a pool is designed to work over a narrow range that is typical of pool applications, I would not believe its accuracy for anything over 20ppm.

Your points are all accurate. However, what I didn't take the time to try and explain is the following.

I don't see the need to "digest" (oxidize) any mold or algae when doing a pressure wash - only to kill it. I would think an application of a fairly mild solution left in contact until dry would kill what grows on houses. Then the pressure washing with plain water would remove the dead material along with all the other dirt, spider webs, etc. This would eliminate any overspray with a stronger solution. And of course the type of surface (vinyl, wood, stucco, etc), type of algae/mold (if any), and amount of accumulated "dirt" is also a factor in devising a safe procedure.

The only other solution I can see with a contractor or landlord intent on using harsher solutions is to wet all plants first, and then follow immediately afterward (or during) with a rinse.

[newnick]

I've been doing this for years on the soffit and facia on my house that has plants and bushes and now a few palms all the way around it. I've seen no damage to any of the plants. I usually add about a quart of bleach to about a gallon of water in a pump up srayer. Hose down all the plants pretty good with water, spray the eaves down real good with the bleach, let it sit a while or brush it with a telescopic rv style brush, hose the eaves down with water and then hose down the plants again. I don't use a pressure washer because I have low eaves and I don't want to tear anything up.

[BlufftonSC]

Thanks everybody for the thoughtful replies. The last time this was done was in the summer and the plants looked bad for quite a while. But, the guy who did it then didn't spray down anything before OR after he cleaned, so, I was curious to see if that would help. Personally, I'd like to use something other than bleach. Any recommendations for removing mold? I'm sure whoever we get will use whatever we supply them with if those are the terms. I just "love" vinyl... it's so maintenance free... LOL! That's a good one, huh?

[_Keith]

Thanks everybody for the thoughtful replies. The last time this was done was in the summer and the plants looked bad for quite a while. But, the guy who did it then didn't spray down anything before OR after he cleaned, so, I was curious to see if that would help. Personally, I'd like to use something other than bleach. Any recommendations for removing mold? I'm sure whoever we get will use whatever we supply them with if those are the terms. I just "love" vinyl... it's so maintenance free... LOL! That's a good one, huh?

I have vinyl siding and answered your question earlier in the thread, Krud Kutter. I have used this product for the last several years with no damage to my plants. But I do rinse them down well, before and after.

Keith