Believe the tile store. FIrst off, although I've never done one.....yet...., I know of many in here who HAVE had river rock installed for their shower floor. Secondly, they're also right in that if it doesn't drain properly, then it's on the installer for not pitching the floor properly.

I'd say it's time to find another installer, because if things screw up, he's going to put it all on you for your choice.

I've done several pebble floors.

I simply increase the pitch of the floor a bit (min 1/4" max 1/2" per foot) and really work to meld the edges of the sheets together. If I can't get the edges to meld, I remove some or all of the stones from the mesh backing and set them by hand.

Tedious, but it looks so much better than obvious sheet edges in the tiled floor.

Depending on the size of the pebbles or stones, care needs to be taken when grouting as well.

You don't want too much grout, which will make it look like little bitty tips of stone sticking out of a sea of grout, and likely result in shrinkage cracks in the grout, nor do you want too litle grout so you have deep valleys between each pebble.

It's a Goldilocks thing.

Mongo

I love the look of a pebble floor too. A nice compromise would be those irregular flat type broken, tumbled pieces. It's a similar look, and since the pieces are flat there would be no hills and valleys for water to collect in. Another option is to use a smaller pebble, as they are flatter.

I would agree with the tile store too--as someone I respect says, "if someone tells you who he is, believe him."

IMO he's basically saying he can't do the floor. Believe him. If you want that floor and nothing but that floor, find another contractor (maybe one recommended by the tile store?). It sounds like maybe he's hoping to get out of it anyway, so it shouldn't come as a huge surprise.

A compromise is what blondelle recommended--that's what we have (onyx slices) -- they have the irregular look of the pebbles, but are flat and much more regular *on top*. Costco is even selling them now for a very good price (around $7.50 sf online). They still need good even grouting, but nowhere near the issues of the round-top pebbles. If you could live with those, maybe you could avoid having to find another installer and still have the look you want. Or maybe he's just so scared now that he couldn't do those either...?

Agreed.

The flat stones are much easier to grout.

Much much easier.

Mongo

I love the look of pebbles, but at the tile shop they had a sample out. I took my shoes off and stood on them--very uncomfortable. Try standing on them at your shop.

Piling on to Trudy's post, which brings up an excellent observation:

There are different sizes of pebbles available. From fairly small to rather large, more like small stones instead of pebbles.

Most definitely make sure they are comfortable underfoot. If you find the right size, it's like a mini foot massage!

Mongo

We put in a stone shower floor that is actually sliced stones, not the rounded stones. I walked on the rounded stones at the store and didn't like the feel of them. The sliced ones are uniform, like regular tile, so maybe that is a compromise. I think there is still more grout than with regular tile, though. My installer sloped the tile a bit more than normal, but wasn't too concerned with mold. You can see them in the link below. We haven't showered there yet, still building, so I don't know how they will hold up.

Here is a link that might be useful: Pebble tiles

I was also "talked out of" a pebble floor by my GC, for drianage, cleaning, and safety issues. I used the flat tile mosaic that is mentioned here as an alt (which still seemed to take a while to install/grout). I like the texture and interesting pattern, and to reiterate the excellent point here, I was able to walk barefoot on a sample which really changed my mind. I DEFINITELY recommend doing that with any texture floor, it feels different and you have to like it every day!

If you've walked on the pebbles and loved it, get them. Its your house.