A tile shower drain is not so ordinary.
It's more than you see when you look at a shower floor.
Why??? It's because shower floors just naturally leak.
See, that grout between the tile will not hold water back.
Water passes right through the grout.
Down goes the water to potentially cause huge damage to all the area around the shower.
The shower pan is all that holds it in.
For a normal masonry shower pan, the only waterproof layer is actually built into the mortar base.
And that waterproof layer isn't mortar at all.
It's actually a vinyl sheet sandwiched between two mortar layers.
All that is invisible from the shower floor, of course, because it's all built into the floor.
What's that have to do with the shower drain? Just this...
There are two drain levels in a tile shower drain.
The upper drain is the one you see in the floor.
The tricky part is the lower drain level is actually down inside the masonry floor.
How's that? The waterproof vinyl membrane is installed so it lays right on the drain base.
It's actually sealed at the base.
Any water that makes it down through the mortar contacts the membrane and rolls right to the lower drain holes and away it goes.
How can you have drain holes built into a "solid" mortar floor? That is one of the hidden tricks to building a tile shower and one of the tricks to installing a tile shower drain the right way.
It's just a matter of building in a little layer of pea gravel around the drain holes to keep the mortar back out of the drains.
That's all it takes to keep the drain holes open.
Just little piles of pea gravel.
Simple as that...
But, there's more...