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Hypo ratio

3 parts water to one part hypo. (1 litre hypo 3 litres water). Leave to dwell for 15/20 minutes then rinse off. Just be careful not to let the hypo dry while it's dwelling always keep it wet

 
To start with it all depends what strength sodium hypochlorite (hypo) you buy as you can get 7% 0r 14-15%

Myself I buy 14-15% hypo so on concrete pavers I would dilute it 1:1 to give roughly a 7% strength.

Be warned that hypo can damage certain types of natural stone and tarmac surfaces

 
Another way I have used is to saturate the slabs with water, then brush on undiluted Hypo.

 
Wow! 15% is mental potent stuff to be putting down neat even with the slabs wet :eek:

Another way I have used is to saturate the slabs with water, then brush on undiluted Hypo.
 
I did try on these slabs 1 to 1 it did not make much difference so I sprayed neat and still not great any ideas?these slabs are very bad all with black spots..

 
I did try on these slabs 1 to 1 it did not make much difference so I sprayed neat and still not great any ideas?these slabs are very bad all with black spots..
How long are you leaving it to dwell for? You can leave it to dwell longer but just make sure it don't dry

 
Dilution depends on the surface & how bad the staining is - I get 10% stuff and usually mix 1:1, but have often used it neat on problem areas.

I once used 75 litres on one house!

 
Hypo generally works great at killing moss, lichen/algae growth but sometimes it can be really hard to remove all traces of really old lichen because it has worked its way deep into the surface.

 
If you have used it 1:1 mix and left that to dwell for 40 minutes and it's still not shifting it I would think that's about all you can do. If hypo don't shift it can't think of much else that will

 
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