What are some methods that can be used to seal an OSB subfloor from moisture? And patch small gouges (quarter sized)?
Background: Small Bathroom remodel. Tile came up with finger pressure, underneath was Gypsum Concrete (Gyp-Crete or Pyrofill). It was crumbled, mildewed and in loose chunks two foot around the tub, and a foot around toilet and vanity. Removed it all to the door threshold to set new tiles. OSB is in great shape, but there is a tiny bit of mildew on the surface in a few spots and some small gouges where the Gyp-Crete took up a quarter-sized strand. Will either go with HardieBacker 500 or self-leveling concrete to raise floor up to height to tile. To remove the mildew, I've done light sanding and sprayed bleach solution and spread it with a rag. I plan to fill the gouges with epoxy (unless there is a cheaper recommendation. Epoxy is a bit on the pricey side). I'd like to moisture seal the OSB also since moisture has found it's way down there in the past.
Edit: Decided to go with Durham's Water Putty. $2 for 1 lb. of powder that never dries out. Least expensive option I could find.
Safety Note: Gypsum Concrete contains silica which can cause silicosis. If you're going to remove it use a respirator, the type with the rubber face seal and replaceable >= N95 cartridges. Spray bottle water all over the Gyp-Crete before removing it. Don't cut with a saw or hammer it all out. Take a painter's tool with a hammer butt or a chisel, and chisel all around the edges of the room, and the pieces will lift out and pry up. Hammering the Gyp-Crete makes lots of dust, and may make fracture lines a few feet long. Possibly where you don't want it broken. When it's all out, spray more water and use a wet rag to clean up the dust/debris. Sweeping or vacuuming with a shop-vac will put all the dust in the air == bad.
