Tips for working with self-levelling compound
If the liquid leveller is not totally contained, you will end up with a big mess on your hands and probably have to re-pour the floor leveller. Seal all holes and seams in the plywood with caulk. The leveller will drain through an opening as small as a nail hole, so be thorough. A good choice for filling those holes and cracks is the type of caulk that goes on white but turns clear when it dries because you can tell when it’s done setting up.
Taping over the caulk isn’t required but it’s a terrific way to avoid stepping in a glob and tracking it around the rest of the house. When working on an older house with floor planks instead of plywood, cover the whole floor in self-adhering roofing underlayment.