Yeah, I agree with Jerry. Silnylon is not very water proof by itself when under any sort of long term pressure (like sleeping on wet ground.) And, like you say, it is very slippery. Once coated with a mixture of good silicone calk and mineral spirits, it is very water proof, not very slipery, and is fairly durable (though not as durable as PU coated nylon.) I made a couple tents using this for floors. I usually use a mix of about 1 part calk and 10-15 parts mineral spirits. I do both sides, doing the inside first one day, and the outside the second day.
I have a couple tents with PU coated floors that I really like, but, one of them has dried out a bit and started to crack. I coated this with the same thing, and it "seemed" to work. But I use it only 6-7 weekends a year when I am out with the family members. Hard to say if it actually sealed, since I am pretty good about picking camp sites.