vaniljestang

Bleach will try to oxidize and destroy everything it touches. Which is why its great at killing moss, mold and algae, because it penetrates the cell wall easily. Larger plants will take a beating and their cuticle helps protecting them from direct oxidising effects. Im not saying a really concentrated hypochlorite solution with a surfactant wont cause burns, but its easy to rinse the plant foilage with clean water when you done spraying the roof. But always buy a sprayer without metal parts as chlorine will cause oxidation(rust), Sodium hypochlorite is good for DIY´ers on the cheap, but the industry standard for cleaning dirty roofs is Benzalkonium chloride - Wikipedia Which is unregulated and available to the public in Thailand on lazada.

My interpretation of why global obesity is increasing: Processed foods taking over the world.

As you see this video, a tropical typhoon can imtate the effect of a pressure washer. The tiles in this video didnt have enough overlap and enough pitch. But even a properly laid tiled roof wont be able to stop the water from coming in if someone shoots water horisontally, or even worse, upwards against the overlapping tiles. What I would do in your situation is to use a chlorine solution in a low pressure sprayer with some dish soap. There are also ready mixed anti mold mixes in 4-liter bottles with a nozzle in my country that you attatch to a gardening hose that can easily reach 10-20 meters. If you are not comfortable standing in a ladder with a low pressure spraying system, maybe rent a lift and spray the roof yourself? And if you use high pressure instead of chemicals from a lift, some water leakage through the roof a hour or so will dry up and probably not damage your home.

Before thinking of using a pressure washer, make sure that you have a secondary roof/membrane underneath the concrete tiles. Use a ladder and push up a tile to check whats underneath the tiles. Even if you instruct the workers to pressure spray downwards, and not upwards, water will always find a way through a tile based roof when high pressure is involved. Chlorine isnt harmful to your garden, its actually a macro-nutrient for plants. And it has a tendency to stay inside the concrete tile and reduce future growth. Stronger chlorine mixes are better. I use pool shock and make a mix right before I spray the roof with garden sprayer. With a strong chlorine mix, there is no need to use high pressure. And you can use this trick to clean dirty walls and outside concrete floors of growth for pennies. Sometimes household bleach is left in stores for years, and will greatly lose its potency, thats why pool shock is better value. And as other people in here have said, using a wetting agent like dish soap to reduce evaporation and increase contact time is a good idea. If roof tiles get cracked from walking on them, they are very easy to replace as long as you have spare tiles on hand from the same manufacturer. Tiles dont crack because of water pressure, but the weight of a man can split them, as they are just made in a mold from sand and cement with no reinforcement.

Here in Norway we use chlorine to kill moss on concrete roof tiles. Chlorine is also effective against mold. Try to use a mixture one part household bleach and 2-3 parts water and spray it on the mold when the sun isnt up. Cheap and effective, and doesnt damage concrete tiles. Be careful with the pressure washer, since the tiles might not have enough overlap to stop ingress of water.