Bill wrote:
::: Paint it with yogurt.
::
:: Would that work? There are 22 square yards of wall. It would need
:: a lot of yoghurt. Any particular flavour?
::
:: Bill

You wouldn't need a fantastic amount - thin it down as has been suggested,
either with water or milk and put it on via a spraygun...you'll find that it
will just run off very dry rock, so you may want to damp it down first with
the hosepipe and then use the sprayer....you don't need a thick coating of
yoghurt, you just want a very thin 'misting' on the rock, to encourage algy
and other microscopic plants to flourish.


HTH