I got an island whirlpool bathtub from an auction and want to put into the existing alcove to replace the 50 year-old cast iron tub. How do I ensure that there is a snug, watertight fit between the walls and the downcurling lip of the tub?

I don't have much room for a plyboard shelf to rest the new tub on so wanted the back edge to be virtually flush with the wall. I was thinking of laying some sort of membrane under the tub lip and then nailing it to the studs about six inches up and then covering with drywall with caulk at the base joints to make it fully waterproof.

Do you think this would work?

I did that too, replace a tub with a drop in tub. It leaked. I then used a lot of silicone caulk and sealed the rim then 'added' a border tile completely around the perimeter where I had wall.

Hi Doug, thanks for replying.

What did you use in the seam between the tile and the tub?

Would ordinary grout do it, or should it be something else.

I put as much 50 year clear silicon as it would hold. I also set my tub in a mortar base so it would not move or flex and open the silicone seal. I then put the border tile on top with 35 year silicone [water soluable] clear caulk and wiped clean