[Roland S]

hi

i've been doing a big teak sandstone patio today. after cleaning there's some bad stains in places. i assumed it was black spot (there was some in places) (although it's more a green than black) but a strong hypo mix wont shift it and pressure certainly wont. apparently the patio was sealed with lithofin sealer when it was first laid if that's relevant but hasn't been sealed for a good few years before i cleaned it today. here's a photo of it has anyone got any ideas? (click the thumbnail for the full size image)

thanks in advance

roly

[Jettaway]

Not sure about that,

Theep only thing I can think of is some form of acid stain. Have they tried to clean it themselves before you with hydrochloric?

[chris scott]

Nowhere for the water to go ...it's gone mouldy.
It will keep happening till you strip it.

[Kenny83]

Hi Roland the stone is a sawn, high porous indian sandstone, the type is called teakwood, lovely looking stuff, I had the same problem a few years ago, same staining, it's actually algae and you may need a few applications of hypo left to soak in over night as the staining is actually in the stone, deep down in the stone, due to the porosity of it.
I went back 3/4 times to a job just putting hypo down then leaving it over night to soak down into it.
Hope you sort it mate.
 

[Roland S]

Thanks for the advice guys. I did leave sone hypo on it overnight when I left today. I've got to do ghe back of the house tomorrow so I'll reapply some more when I get thete and see how it goes. Thanks again