Does anyone have any experience with this ? I read on Google that the surface should be sealed every 7 or 8 years; my Mother in Law hasn't done this in the 40 years or so since she had the place built and it is now gathering black/grey patches on the north (sunny) sides.
On the south side randomly pink patches come and go but seem to be less of an issue as are more seasonal.
Any help appreciated to save going down the wrong track; might even look at sealing it once we can get it clean !!