Sealing paving and treating algae

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I thought I would follow up on my last post about treating the stone paving at my Bristol home. The Algon algae treatment was easy to apply and after a couple of days I could see that moss and weeds between the paving had died. The instructions said that the product would take about 7 days to activate and I noticed that, after about a week, that the algae had blackened and was less slippery under foot when wet. So I would say that the Algon was a qualifed success as the sloping pathway seems safer but the downside is that the stone is discoloured with the dead algae and I reckon I need to get the Karcher pressure washer out again. The problem I found with using this tool was that the jets are so powerful that the algae was washed away very effectively but so was much of the ageing cement pointing between the stone! I am giving some ideas about sealing new slabs below and now wonder if presssure washing my old stones and sealing them might be the best answer….?
Protecting patio stone from algae and discolouration
If you are having a landscaping job done such as having a new terrace or patio laid, it is well worth treating the stone with a sealant. For sealing and protecting stone, the Italian company Fila produce a range of quality products for treating stone and concrete slabs. Sealing the slabs will reduce porosity and therefore staining in the stone and will also give less purchase for algae; if your stone is laid in a shady area, it will very likely suffer from moss and slippery algae, especially in the winter. Sealant will also give protection to the stone from surface erosion.
The manufacturer recommends using Fila Hydrotep on new stone as a primer, followed the next day with a coat of Fila Fob which gives a matt finish and enhances the natural colours in the stone. Coverage varies according to the porosity of the stone; the manufacturers give 5-15 square metre coverage per litre. The stone must be dry when you apply the products and should be used when rain is not forecasted for at least 24 hours. You can also use it for concrete slabs and terracotta tiles.
There are quite a few other products in the Fila range including Fila Stoneplus which is a good colour enhancer and Fila Wet which, as the name suggests, gives a wet appearance (see photo above) which looks good on dark stone such as slate. Henry has had good results on a number of his landscaping sites in Bristol with these products.