Shortly going to have new oak beam, dried not green, fitted to kitchen ceiling and then ceiling plasterboarded out and skimmed. Had a few plasterers around some said do the whole ceiling then put new beam up others said beam first then plaster. My question relates to what one said who favoured beam last in that he stated the skim if it comes into contact with the oak will turn it black. I know ammonia fumes can turn oak black but plaster no idea.