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When I was a nipper I remember my Grandfather - who was a
farmer in a small way in Gloucester - using balls of whitewash
(limewash?) on the walls of the cowshed, and a walled garden.
It was extremely effective. I've recently acquired a long old brick
wall and would like to use Grandad's method to make it presentable
but when I ask around all I get is blank looks.

Anyone any ideas please?

Limewash is still used on historic buildings; try a DIY or building ng.

Janet.