We have recently had an extension done, all signed off and the builders have done top job. We went away last week, and when we got back we’ve noticed some green mould. It was very hot last week and we left no ventilation. Most of the mould was on skirting in old part of the house we built off, this was probably because the plaster in this part was still drying and was tacked against it (its an open plan extension connecting to our old living room). However in the extension the plaster was already dry and we had done our first mist coat but at the bottom on the plasterboard green mould is sprayed across it. Its is powdery and just wipes off but i’m just worried about skirting and flooring it and it coming back. Guttering is all fine and there is more than adequate space below with air-blocks. As damp rises I wouldn’t expect the adjoining extended room which is still drying to cause this at the bottom of the wall?