When my house was build about 2o years ago, I had a water problem in the garage that was finished to the floor with drywall. I replaced the wet drywall with greenboard, but now the white cover in the greenboard is sluffing off. The water damage seems to be coming up from the floor and is about 1 foot high now. The issue seems to be the water gets on the board during the winter snow, but I also have a lot of springs on the property and I suspect that some is under the floor, although not visable. Can I use Kills and then a waterproof paint on the greenboard since it looks like hell and I do not want to tear is all our again. PS - I am not a handy guy!