My guess is they were made at the same time as the tile work was done , everytime you drill into a tile wall you have the chance for water to get in there behind the tile in fact I do not like niches in the shower at all i find they never drain right and they collect soap scum

Thank you for your comment. Well it's a bit too late for us. We already have the niche. Just wondering if that floating shelf can be added to a pre-made niche. If so, can anyone give me an idea of how that is done?

I agree with Patricia--The floating selves were added when they did the tile. My husband made a niche for our shower in the last house we lived in and all of the decisions of where the shelves would be along with where the niche went had to be decided before he put the tile up. You would have to take the tile off and practically take the niche apart to put up the shelves.

Thank you for your response! =o) So the niche has not yet been installed. We have bought one of those pre-made niches. So the niche has not been installed in the wall and therefore no tile has been put up yet. I'm trying to figure out if and how the shelf is added. Like the actual step by step instructions. Does that make sense? If I want to diy a floating shelf into a niche that has not yet been tiled, what are the steps?

Google it. Watch a video

I have google searched and houzz searched and youtube searched and Pinterest searched all before I posted on here. Couldn't find the answer. I don't want a shelf that goes all the way across. I want to install one that goes half way across like the ones in the picture. Maybe I'm using the wrong key words. I'm open to any suggestions.

I understand that for shelves that go all the way across, (so touching the niche on three sides) grooves should be left in the tile to slide the shelf in. But if the shelf I'm looking to build only goes half way across, will creating a slot in the tile be enough to support a shelf that is only touching the niche by two sides? Or is there some kind of bracket or something that I need to attach to structurally support the shelf?

I'm always amazed by how strong tile and thinset is. As long as the shelf isn't too deep or long I would think it would hold wirh just well cut tiles around it and thinset under the tile and behind the shelf. Did you ever get an answer??

I made one of those myself, but built it before I tiled it. I doubt you can do it father it's been tiled.

Don't know for certain, either, but you might consider not entirely "floating" them, as such but have them extend from a center board OR have shelves hang from a tension rod (perhaps w/industrial strength adhesive added to the ends for strength) You could upside down legs from which to hang shelves -- maybe cedar boards (one shorter than the other ) prepped for moisture -- using these kinds of legs used upside down (come in different lengths) to hang the different length boards for different width shelves:

https://jmhaotian.en.made-in-china.com/product/qXonbFZDkSpa/China-Furniture-Fitting-Office-Table-Metal-Leg-Removable-Metal-Table-Legs.html

OR

https://www.potterybarn.com/products/triple-hanging-shelves-wood/ if you can figure out how to hang the brackets without damaging the tile.

thanks

thats perfect

I searched everywhere too and my contractor couldn't do it or a full glass shelf for that matter, because my mosaic accent tile was too "irregular". Very disappointing, as now I have a tall niche with wasted space, or I have to attach brackets and risk breaking waterproofing seal. (I used a plastic RediNiche. This and other issues have taught me to make sure the "experienced" contractor can do all requested design elements before hiring.