The stall mats are not made to be used alone but with bedding, the bedding soaks up the pee and does not go under the mats, at least it hasn't for me and I've installed them myself here and the farm I used to live at. Sand or dirt bottom soaks up the pee as well and you can't get it out without digging out the wet spot which leaves you sooner or later with pits, holes or uneven stall floors which aren't good on the horses backs and you end up every year having to buy more fill sand , dirt or bank gravel which ever one uses to replace what has been taken out. The reason I went to the stall mats is because I am always left with an even stall floor which has a nice give to the joints. Because of having COPD I couldn't take the amonea pee smell in the stalls and it was stronge! there was noway to get it all out and most horses pee in the same spot over and over and it gets pretty soaked into the dirt and ground and really fermints. It is just my experiance with it. You could always try the sand if you think it would work for you, if it doesn't all you would have to do is level it out and or replace they wet spots and place the mats on top and use a nice bedding. I recomend the equinefresh pellets I love them.
Cathy C