Cleaning render

[cwr]

Hi folks

Any recommendations for something to spray on render to get rid of green algae? It's a white thin coat Weber render. Plenty of trees near by so guess I'll be doing this every couple of years...

Thanks

[ProDave]

I spray with diluted bleach from a spray bottle.  Best done when you are expecting rain shortly afterwards to wash it off.

[saveasteading]

4 minutes ago, ProDave said:

from a spray bottle

Or a garden weedkiller in a garden spray, as they can usually scoosh further. .  Do NOT use a pressure washer or you could lose the render.

[nod]

pick a dry day 

Dilute 3-1 Spray on Pump sprayer or what ever you have 

Let the rain do the rest 

[cwr]

Thanks for the replies and suggestions.

I had tried diluted bleach but it had no effect, it may have been too weak a mix though. 

[cwr]

Just report back, I looked for algon but our local place had patio magic so trued that. Did a test area and was very impressed with the results. 5l diluted as per the instructions applied with a weed sprayer did the whole house. The photo shows the test area after 3 days. 

[cwr]

Wasn't until I did this that I realised just green it had got in only 3 years!

[jack]

Any of those products are fine. I've used Sika mouldbuster(?) in the past, but this time around I bought this stuff on sale and it worked just as well: https://www.amazon.co.uk/dp/B017PD8S3U

 

It appears to have the same ingredients and concentrations as others I looked at.

 

As others have done, I just mix it up and spray it on from a weed sprayer. Bit of a ballache getting to the highest part of the walls, but I only need to do it every couple of years, so not a bit deal.

 

It's like magic - 48 hours after application and the whole thing turns white!

[ProDave]

I did mine a few days ago, my usual 1/3 bleach 2/3 water in a hand sprayer.  Used about half a bottle of bleach in the process.

 

I chose a dry day with rain forecast next day to wash it all off and it is all clean again.

 

but it was nowhere near as green as in the pictures above.

 

I do this about once a year now.

[HerbJ]

47 minutes ago, jack said:

past, but this time around I bought this stuff on sale and it worked just as well: https://www.amazon.co.uk/dp/B017PD8S3U

Wet and Forget is similar to this and also works like magic on render and patios and it may be cheaper. Costco seem to do the best deals on this  https://www.costco.co.uk/Grocery-Household/Cleaning-Laundry-Products/Cleaning-Products/Wet-Forget-Concentrate-Mould-Lichen-and-Algae-Remover-5-Litre/p/128234

You can get a Gardena Backpack sprayer withe extended lance  set that we have used to spray up to our gutter relatiively easy.  https://www.gardena.com/uk/products/tree-shrub-care/pressure-sprayers/backpack-sprayer-12-l/970477401.html

[SteamyTea]

Depending on the fungal type, temperature, humidity and exposure to UV irradiation, either an alkaline, or acidic, solution can stimulate growth.

Fungi are a natural miracle when it comes to survival. Have outlived just about everything on the planet.

[MPH243]

I used the same stuff as @jack, within 2 or 3 days it had all gone. 

 

I bought this sprayer https://www.buyaparcel.com/matabi-81847-berry-7-sprayer-5-litre-mtb81847/ with the 5.4m extension

 

https://www.zoro.co.uk/shop/maintenance-and-outdoor/lawn-and-garden-sprayers/telescopic-lance-5-4m/p/ZT2594450S

 

The extension works OK but it is a bit whippy when fully extended, and the locking system is friction only so does undo a bit to easy. It is definitely worth it as no ladders needed to reach the top of my gables.

[jack]

On 23/04/2025 at 21:18, MPH243 said:

... with the 5.4m extension

 

https://www.zoro.co.uk/shop/maintenance-and-outdoor/lawn-and-garden-sprayers/telescopic-lance-5-4m/p/ZT2594450S

 

The extension works OK but it is a bit whippy when fully extended, and the locking system is friction only so does undo a bit to easy. It is definitely worth it as no ladders needed to reach the top of my gables.

 

That extension looks useful. Do you think it would fit a generic pump sprayer? How does it connect?

 

On 19/04/2025 at 13:16, HerbJ said:

Wet and Forget is similar to this and also works like magic on render and patios and it may be cheaper.

 

Am I missing something Herb? Those are twice the price (Costco = £40 for 2 x 5L (minimum order), my link £40 for 4 x5L).

 

If you want less, here's 2 x 5L for £28: https://www.amazon.co.uk/dp/B017PD1REM

 

Both are concentrates that need diluting 5:1.

[HerbJ]

No, I my mistake - I wasn't concentrating and missed the 4x .....ugh

 

 Apologies

[MPH243]

@jack I tried it with a Hozlock one and I could not get it to fit, I thought about trying to by the fittings to adapt it but just bought the sprayer as I was not sure what threads I needed. 

The sprayer is good quality as well, it screws onto the pipe instead of the short Lance. 

[Adsibob]

Is it really not advisable to use a pressure washer and just water? My contractor who installed the render has cleaned my render this way and it worked fine. I have ceresit render and appears very tough. I was trying to mark it once before drilling into it and even hitting it fairly hard with a screw driver didn’t do much damage. I ended marking my hole with a felt tip pen instead.

[Andehh]

We have Johnstone storm shield thin coat, I think it is, and I tried a pressure washer on a section that needed redoing. At about 6-12" you could blast the white off the sort of mini beads inside, but over two feet away and at an angle 'seemed' fine! I don't go about closer then about 3-4 feet to be on the safe side.