Dirty Patio

I have just had lunch with a friend, Olive, and we have been looking at her patio which is quite old. It looks black and dirty. She has had it cleaned (power washed - I presume) several times in the past. Not only is this expensive, but the black comes back again eventually.

My own thought is that the patio is made of concrete slabs, which don't get dirty in the first few years, as the chemicals in the surface of the concrete kill algae/bacteria. However once the concrete has weathered for a few years that effect wears off and you get black staining.

Does anyone have any other ideas on what causes it? Is there a cure - ie is there a chemical treatment you can use? Olive is think of having a new patio laid - its uneven and probably worth doing. Are there any materials that won't stain in the future? A lot of people seem to be using natural stone from India. Is natural stone immune to this?

 

Wouldn't the trick be to just give it a dose of caustic soda and then a good seeing to with a good stiff yard brush, followed by a thorough rinse a few hours after the caustic soda had done its magic?

 

You will always get algal build up particularly if the area is shaded.

A proper industrial machine will remove all traces including lichen but to maintain an algae free surface you will then need to regularly apply patio cleaner or weak bleach solution and scrub this in then rinse off. Any contractor leaving lichen rings is not using a proper machine.

Even if you get new slabs you will still need to regularly clean it.

The price of pressuere cleaning with a profeshional machine is always high as they are expensive machines and use a lot of fuel to run and take time to set up and pack away.

For this reason I charge pressure cleaning at £30per hour. Dont compare this to a £100 B&Q karacher though as an industrial machine is putting out around two or three times as much pressure and water volume.

 

I ended up buying the Kaarcher 5.85 which has a working pressure of 125 compared with the usual 80. It does clean the lichen rings etc but you need to work fairly close up and of course it takes longer. But once done its then a matter of going over it regularly.

The t-chaser is ok for most dirt but not the stubborn.

and yes the pointing does get blasted out - almost impossible to avoid imho

 

Funny, just a few years ago people were painting yoghurt and liquid manure on all sorts of garden stone work just to make it look gungy.
Admittedly that was rockgardens and walls etc.

But I cant help thinking we do have some very strange requirements from nature.:D

 

Are those rotating patio brushes that Karcher sell any good for this job?

I thought they had a number of different models, but the only one I can see on their site is the T300

 

Mnay thanks to you all for your comments. Other than polished granite, it sounds like all patio materials have the same problem. I laid mine 6 years ago, and for most of that period it looked very good, but it is looking tired now.

I think this friend Olive has already made up her mind to have a new patio. Tho old one wasn't laid very well and is uneven. I think she has just got to go ahead and get what she wants, and worry about the cleaning when the problem arises.

Shiney your patio looks superb, it seems a shame it is not imune to all these problems.

 

It looks blinking smart to me!

Do the trays of pots leave rings underneath them? I got told off last year :( and will put plastic sheet down this year (in our conservatory which has Indian sandstone); I'm also experimenting with whether I can put some pallets down first - so that there is air under the plastic sheet and its doesn't get dank.

 

There is a caustic solution (the stuff the farmers use to clean up their milking sheds etc) which works great mixed at about one third to two thirds water or even 50/50
It must NOT be used on tarmac though .. it eats it away
Spray it on, leave it for an hour and then just wash it off
Everything as clean as a whistle
Obtainable from your local farm supplier
Don't get it on your hands etc ........
I used it with a knapsack sprayer some years ago and it ate away at the plastic nozzles. I now use a galvanized watering can
Rough stuff it can be, but very effective.
All liability for mis use denied

 

Don't spray caustic soda solution. Use a watering can on a day when there is little wind. It is effective but extremely nasty stuff. If you spray it and the wind blows the vapour at your neighbours, they will sharpish know about it when their lungs start burning and their eyes will sting like crazy.

I believe you can get caustic soda in crystal form. Then you'd just scatter it directly on the surface to be cleaned then water it gently to start the reaction. Leave it for a while, then wash it off throroughly with plenty of fresh water and a good stiff yard brush.