I've witnessed on many occasions painting contractors scraping the old loose paint off buildings with pressure washers. I'm sure that this does a reasonably good job at removing the loose paint, but it seems like it would drive a heck of a lot of moisture into the wood or brick that is going to be repainted. Is this an advisable practice? If it is done, how long until you can spot prime and repaint? Is there a benchmark moisture level, above which you can't paint the material?