I was told that the previous owners of our home had a problem with bathtub falling through. This was about 18 years ago. It was repaired. It is a cast iron tub ( I guess that is the correct name- anyway it is one of the heavy tubs ). The other day my daughter (adult) sit on the edge of the tub. When she did she heard it creak and felt as if it went down a little.If this is getting ready to break through again, is there a more secure way it can be fixed than the orinary fix? Also what type of tub material is best? Any suggestion would be appreciated. I am scared for anyone to get in the tub. Also when it was repaired before I do not think they put the tub back up high enough because we have such a hard time keeping caulking between the ceramic tile wall and the tub. We have even tried marine caulking.

It was not installed correctly! Every tub has its limits, weight wise, but they are very accommodating for every person. If you have to put a lot of silicone on something plumbing, you need to call a plumber. The ONLY silicone on a tub, should be on the edges, not to stop drainag.

The other day my daughter (adult) sit on the edge of the tub. When she did she heard it creak and felt as if it went down a little.
That's not a good sign. Something in the floor joists gave way and the only way to tell is open up the ceiling and look. You may have to head off and beef up your supports. Good luck, Tom

I agree with Tom, this is not good at all. When I started to read your post I was prematurely thinking fiber glass tub, which are lnown to creak when not properly bedded with modified thinset. After reading the entire post I think that old fix is about to go south on you. Tom gave you the only option, open the ceiling below and add new, proper support to the tub. A cast tub weights several hundred lbs even without a person or water in it.