I am assuming you mean a pebble mosaic tile. If you use shaved pebbles, it isn’t too bad.

We have a pebble floor in our shower and I’m guessing it’s not any more difficult than a shower floor w/ a tiny tile floor. And it’s DEF easier to clean than the plastic tub we used to have. And it’ll be under your tub so it won’t be getting nearly the same kinda use As out shower floor. One word of warning tho: we chose “white” pebbles and found out they’re really not white once we started scrubbing them. They just had some kinda white coating on them that came off over time. Hope this helps.

I believe that you are talking about piling up loose river pebbles under your tub, to give it an outdoor feel. I have seen this done in pictures and wondered how they clean them, too. Remember that a bathroom is where we are naked, with all those skin cells falling off of us as we pull clothing up and down. This is what makes up a lot of dust. Have you even been in someone's bathroom where there is a paneled cabinetry style and you see white dust hanging out all over the raised panels? Skin cells and powder. Your loose stones will get that dust, the dust from tearing toilet paper, and aerosol over spray. It seems to me that at least once a year you would have to remove the loose stones, clean well, wash off the rocks themselves and let them dry before returning them. And you have to vacuum them with a soft brush occasionally as they lay on the floor, too. Too much trouble unless you have live-in help who are sometimes bored.