Plaster behind tiles or a waterfall out of the spa??

[SoonerSaint]

I'm curious to know if you are suppose to plaster (seal) behind tiles? So you would put ?? around the tile line and then go back and mortar your tiles?

What about on a rock waterfall or weeping wall out of the spa and into the pool? Do they seal that concrete prior to placing the rock? Thanks.

 

[JasonLion]

Normally tile is applied before plaster, and the plaster comes up to the tile and fills in-between the tiles, creating a waterproof joint.

Often concrete waterfalls are sealed before stones are placed on top. Other times the stones are mortared in and the mortar seals things.