How to clean a retaining wall?

[Rolfe123]

I am currently trying to remove mould (which is black )from my retainer wall. I have tried bleach, dishwashing liquid, white vinegar and baking soda to no avail.

[MitchellMc]

Hi @Rolfe123,

It sounds like what you need is water pressure, and I'd recommend you consider purchasing a high-pressure washer. Even the budget-friendly versions will do a wonderful job of blasting the mould, moss and mildew off the wall. Once you've removed the bulk of the material, you can then look at the chemical solutions to remove any remaining staining. However, the pressure washer will do the lion's share of the work and have the wall looking almost new again in a short time; it's also one of the more rewarding cleaning jobs around the home.

Please let me know if you have any questions.

Mitchell

[Rolfe123]

Hello Mitchell,

It is because I have used my high pressure unit with no results that I am at a loss as how to remove the mould.

[Remarka6le]

Check to see if your local Bunnings has a High Pressure Cleaner you can rent, 4 hours is around $41. I find they have more power than the models you can purchase in the store, last time I hired one it made quick work of brickwork that looked similar (if not worse) than the pictures you're showcasing. Coupled with a range of chemical solutions that @MitchellMc displayed, you'll get rid of most of the mould. 

[J-P]

I am sure you have ensured this, but was it kept it in right mode and used as close as possible to stone. I have always had success in removing mould using a basic electric pressure washer

[MitchellMc]

Hi @Rolfe123,

That sounds a little unusual, as with a high-pressure washer, you should see some amazing results. And was it a powered unit like one of these? It sounds a bit silly, but was the unit turned on? I'm absolutely certain that you'd be able to remove at least half this build-up with a high-pressure washer.  To have no results, sounds like the machine is faulty or, as @J-P mentions, the nozzle is not being held close enough. Typically, the nozzle would be held around 10cm from the wall. It can be slightly slow going, but the water should blast that material right off.

Mitchell

[Rolfe123]

Hello Mitchell,

The Gerri  3600 is the unit I have and had no problem with it at all. The mould I have is deep seated into the stone.

[EricL]

Hello @Rolfe123 

The mould must be imbedded very deep inside the pores of the retaining wall. I propose trying 30 Seconds 5L Spray And Walk Away Concentrate. I recommend using Aqua Systems 2L Garden Pressure Sprayer to spray the concentrate on your retaining wall.

Please make sure to wear personal protection such as gloves, goggles and a mask. Please make sure to follow all the safety guidelines printed at the back of the bottle.

If you need further assistance, please let me know.

Eric