Just had a large patio laid in Indian Stone. The workman used brushing sand and cement mix brushed into the joints. I now find, after some rain, that the lovely colours of the stone is now cement grey. I have tried wetting and brushing hard to no avail. On wetting and brushing the colour does reappear but goes back to grey as it dries. Any ideas on how to remove the staining so that the colours reappear please.
As you can imagine I am very upset as it has cost me a fortune. I need to know how to bring the colour back to life so I can put my foot down with the garden centre that did it.
Many thanks in advance.