Cleaning algae from external walls

By The Helpful Engineer / On / In Existing Building Issues

Cleaned boundary brick wallWith our damp and warm climate, algae growth on external surfaces can be a problem. I generally just use a power washer every few years to clean the sheltered concrete areas where it can be a problem. However I discovered that the power washer was unable to remove the algae for my brick garden walls, probably as the brick was more porous than the concrete.

However lightly scrubbing the walls using a dilute solution of water and bleach provides an excellent result with little effort, see below.

Cleaned boundary brick wall

The rendered wall below simply had the water/ bleach solution sprayed on rather than scrubbed and returned great results also. It is also far cheaper and more effective than the marketed brands e.g. fungicidal washes, Jarvis fluid etc. Be careful though and don’t add too much bleach as it will probably kill the surrounding grass and plants and don’t let it come into contact with skin, pets, clothes etc.

Gable wall render cleaned

11 thoughts on “Cleaning algae from external walls

  1. I have patches on my bedroom that look greasy, I have C.O.P.D & Asthma, I believe the house has damp & have even caught a black floppy silver fish, I rent & get fobbed off ,where can I get advice

    1. You need to get rid of excess humidity, the bathroom ought to have an extractor fan with humidity sensor. Some people get annoyed by the sound of the fan running, you can do some research to find the best type.

    2. Also you can get barrier wallpaper that also contains an insulating layer, that helps prevent condensation.

      Also there are heat exchangers that can exchange the house warm moist air for warm dry air taken from outside.

    3. Finally, steam from kitchen cooking should go out via a kitchen extractor fan !
      So overall you need to curtail airborne humidity at source where possible.

    4. Hot water and mbleach or white vinegar can help clean the patches. As an interim solution salt or baking powder in an open container can help absorb some da!o but the landlord should fix it

  2. On properties that suffer from red, brown or orange staining on either rendered, pebble dashed, Krend or slap dashing is due to iron ore pigment in the sand getting wet due to water ingress which then causes them to rust and bleed out through to the surface causing the staining. You will notice on walls that don’t get so much weather or under canopies etc the problem will be a lot less apparent
    I know this because we have carried out extensive test on a variety of sands as we operate a exterior cleaning company
    and found any mined material such as building sand rock etc will nearly always contain iron fragments.
    Visit my website
    to see how by having your house professionally cleaned without doing any damage to your properties external finish can dramatically improve the appearance of you house.
    Painting over the stains is not really an alternative as the stain will bleed through and surfaces such as Krend coloured render etc recommend not to paint as the finish needs to breathe. email

  3. Regular maintenance procedures-daily, weekly, monthly, and quarterly-help ensure cleanroom compliance, no matter what the cleanroom class. For example, positive-pressure air should be running at full-flow in a Class 10 cleanroom for at least 30 min before cleaning to ensure clean, fresh air within the room. Cleaning starts at the highest point and works toward the floor. Every surface, corner, and ledge are first vacuumed, then damp-wiped with a cleanroom wipe. Operators wipe surfaces one way-either downward or away from themselves-since a back-and-forth scrubbing motion can create more particles than it removes. They also use a clean surface of the wipe or sponge with every new stroke to guard against redeposition of contaminates. On walls and windows, the wiping movement must be parallel to the airflow.

  4. The algae are fed liquid nutrients and carbon dioxide to spur growth. Pressurized air is pumped into the panels to further increase growth and prevent the micro-organisms from settling down and causing rot, said Mr. Wurm. He notes that scrubbers in the panels automatically keep the glass clean. The panels double as solar thermal collectors to convert sunlight into usable energy.

  5. I had my pebble dash render soft washed and he told me it was sodium hypo he used when done after a few hours we never noticed any change in the appearance of dash so contacted him to say to which I was told this can take up to 2 weeks to show significant difference is he correct

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