Hi. My parents built an extension to their house 10 years ago and replaced the render finish with whiter pebble dash. It was beautifully white for the first few years and looked great. In the last 5 years or so it has become grey and damp looking and really takes away from the house. (Probably from rain as it faces South-West) I am getting married next summer and I think this is the reason they want so much to rectifiy the problem as friends and family will be callin! Is there a spray or other out there to clean pebble dash? Would really appreciate any help or advice given. Thanks.