cleaning

["Bill Urmenyi" <bill@zzzzzzzzzzzzz>]

I've got a 12 foot square chess board in my garden made up of 18 inch square
concrete red and white paving slabs. I have just cleaned them using a high
pressure water pump but there are some black spots on some of the squares
which cannot be cleaned that way. The slabs are about 18 years old now and
over the years the problem has got worse. Although it is possible to
distinguish between the dark and light squares it is becoming visually
intrusive.

I do not possess a sand blaster so I wondered if there was some cleaning
agent that would do the job without me having to go on my hands and knees
with a scrubbing brush which I am not prepared to do. One difficulty is that
the chess board is inset into my lawn and I don't want to kill the grass.

It is now chess playing weather. Out in the garden with a drink, a nice
cigar and good company; eminently civilised.

Any suggestions.

Bill Urmenyi