Replacement bathtub: steel -cast iron-plastic?
What should I be thinking about in making the decision?

$$$ and weight. A cast tub will last a very, very long time but can weight 1/4 ton. Acrylic and resin tubs are cheaper and lighter but will show scratches after a few years. Nobody makes a plastic tub that I know of, maybe your meant acrylic.

I agree with ballengerb1. Also steel or acrylic tub bottoms should be supported with thin set/mortar to minimize deflection when a person is in it.

Chuck

In terms of serviceability I rate cast iron at #1, Steel at #2 and plastic/fiberglass at #3.
I was the pumbing super on a large division in Sarasota consisting of single story subdivisions and mid raise condos. We installed hundreds of steel tubs in that 8 year project. Out side of a few that were damaged by dropping bottles that fractured the finish we replaced none under warranty. The steel tubs were easy to handle and install and since we bedded down each one we didn't have the flexing and leakage problem that we're hearing about today. Regards, Tom

I am with Tom on this one: NOTHING beats Cast Iron tub. It feels solid, won't turn yellow after couple of years, won't scratch easily, won't have that hollow sound when water hits it - and will last for Century.

Cost wise it is very affordable. Yes, weight may cause problem during installation but this detail can be easily handled. Go Cast Iron, you will not be disappointed.

Good Luck with your project... Milo