Try to get a second opinion from another contractor.

When installing tile in a shower, the rule usually is to lay the floor first so there's little chance the water dripping from the walls would seep through the floor tiles edges.

If you replace them you might leave a gap between the wall tiles and the floor, which might look ugly too.

It will compromise the waterproofing. As a tide you over until you gut it completely kludge, you could tile over the existing floor tile. But, that will lead to issues around the drain, and it is a very temporary solution. You really need to gut and start over. Start planning that now.

I had thought to address the waterproofing issue by taking the floor til (1"x1" mosaic hex) up the wall 8 inches. I guess that must be where the thickness issue comes in? All comments welcome!

Judy,

That is how usually this being done, you remove 1-2 rows of tile, replace the floor and put the same tile if you can find it, if not you use something else and create a border along the bottom. Reputable tile contractor will know what needs to be done in cases like that.

Good luck.

Thank you very much! I thought it seemed possible, but this fellow disagrees. I guess I will talk to someone else. Thank you again.

There is a new product out there EZdraincap its a Drain adapter specific to this type of installation you simply remove the drain grill, insert the new drain extension ,prime the floor with eco prime,bonding primmer and install new tile over tile and your done.

Great idea! There's always a way to get something done without compromising quality. I'll look into the reviews for this product.