Hi all looking for some advice. Am doing a wall in silver sand white cement and lime. I have done a test on the wall. I scratched it with normal plastering sand and cement. 4.1 Top coat is silver sand white cement and lime. 5.1.1. It dried out white the first couple of days , but after it rained, it turned a dirty colour. See photos. Should the scratch coat be done with normal plastering sand and white cement alsoto stop this discoloured look. Any help would be much appreciated.