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How to clean a patio

Updated on January 20, 2012

How to clean a patio

If you own a patio then chances are you have seen first hand how a lovely slab can quickly become covered in mossy green growth or even worse those terrible black spots.

Although rainwater and the atmosphere carry enough dirt and pollution to leave the patio looking tired it is the green and black marks which are the most difficult to remove.

I laid a new patio only two years ago and already by winter time this year it was starting to look grubby, the area that was overhung by trees and bushes was the worst. I guess the lack of sunlight played a part here.

Here is how I cleaned it

The first thing I did was to scrape off some of the excess moss that had appeared in a and around the joints, I used a trough but was careful not to scratch the patio slabs.

I then swept the loose dirt and bits of moss off the patio and then applied a moss killing chemical such as this. I could have used a watering can but that would have involved a lot of wastage and I didn't want to contaminate the can. So I instead used a sprayer such as this, it's important to adjust the nozzle so the liquid comes out as a jet rather than a fine spray. The sprayer meant I could treat the slabs from a distance.

The chemicals

I always buy high strength concentrated chemicals for my roof moss projects such as this, they can be diluted to the desired amount and I have found the tub lasts a lot longer. There are several different products on market but as long as it is a high strength concentrated one they should be fine for a patio.

Other steps I took

In addition to the above I cut back the overhanging bushes and also cleared out the gutters as I had noticed there was a small leak, directly onto the patio.


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Pressure washing

Another option is to pressure wash the slabs but by doing this you run the risk of loosening the cement between the joints and for the most part it is not required. The marks that appear on most patio slabs are not just grub and dirt than can be washed away but it is organic growth that needs to be killed off with chemicals.

It will take a few weeks for the effects of the chemicals to be seen but in my opinion this is the best approach.

Obviously by using chemicals you will want to be careful and follow all the safety instructions. It is better to apply them in the morning on a dry day and never when rain is imminent.


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      Neville Walk 7 years ago

      I made the mistake of pressure washing my patio. Before it had been slightly dirty, but had no moss. After pressure washing it, within a week, moss started to grow on the slabs, and it has been almost impossible to remove it for any length of time. It seems that pressure washing can actually encourage moss to grow.