fiberglass tub vs steel

[ADRamsey]

My husband and I are remodeling a 1972 ranch style home and we are getting ready to tear into the bathroom. We are replacing all the fixtures including the tub, and we've found that there was at some point a severe leak between the fiberglass surround and the top of the tub. The floor has rotted, and we're replacing that, along with some subflooring and a couple of studs that frame the tub. The problem we're having is that this is the third time we've come across an installation of steel tub and fiberglass surround that has had serious leaking problems. The first one, we installed ourselves, and followed the instructions on the caulk we purchased, which was rated for that type of project. We allowed the caulk to cure for 36 hours as directed, and still ended up with a terrible leak and floor problems. The second time, we installed another tub and surround set and though we moved out of the house before it became a problem, we still had a very poor seal around the tub.
Does anyone know of any way to seal a fiberglass surround to a steel bathtub? We'd prefer a steel tub because they're sturdier.
We are open to installing a three piece fiberglass tub and surround, but that opens a whole new can of worms -- I know that that type of tub needs to be supported by sand underneath, and I've also read about deck mud and sand/portland mix being used. When you use cement or a mix, is actual mixed cement? Wet or dry?
Information on either project is greatly appreciated.
Thanks,
Amy

[hj]

I am glad you said, "Sturdier" than a fiberglass one and not "better". There is almost no way to use the words "steel tub" and "better" in the same sentence. A properly, or even improperly, installed tub should not leak at the surround joint because the lip in back would catch the water and not allow it to get onto the floor. Therefore, there was a "real" problem with the installation, but what it was we cannot tell without seeing the actual site. Almost anything is better than a steel tub, but a fiberglass one is not a great deal better in the long run.

[ADRamsey]

The problem with the first tub was that it was used and someone had drilled holes in the lip above the tub rim. Also, there is a place at each corner where the lip is cut on a bias and it comes down almost to the level of the tub's rim. The first tub was off level -- the whole house was off level! -- and so water collected there at that corner and leaked between those bias cuts into the wall. We aren't yet sure what's causing the problem with the tub we're tearing out, but the caulk is gummy and is a nasty mess, there's no seal there to speak of.
I'm still looking for ideas.
Amy

[jadnashua]

Even if the floor is not level, you must ensure that the tub is level and properly supported, or you will get water pooling and potentially creating a leak. Not all caulks are created equal. Especially if there is constant moisture, the caulk can fail fairly quickly unless it is rated for constant moisture or underwater if there is pooling water caused by unlevel installs. Also, some caulks actually can take a week to fully cure, read the instructions carefully. They may be skinned over fairly quickly, but may not cure properly and perform as designed unless you let them stay dry for the time specified. For most tubs, except for cast iron, they "feel" better and often last longer if they are totally supported underneath. This can be done with plaster of paris, a sand topping mix (concrete and sand mix), or possibly other choices. Flex causes a tub or shower base to feel cheap, and the flex creates microfractures in the finish that makes it hard to clean and keep looking good in the long run. Steel tubs flex, too. Dropping something on them can quickly cause a crack in the finish that leads to rust. My unprofessional opinion.

[ADRamsey]

Thanks for the advice. The old tub went out this weekend -- cast iron and my shoulder is still killing me -- and the new tub went in. We did go with a steel tub and we supported the bottom. The tub is level! The leak we'd had must have been fairly old, since the floor underneath was dry, but it was also rotted and we replaced a 4x4 section all the way down to the joists, which were fortunately in great condition. We're putting in the surround tonight. Through this process we've found that what was "standard" 30 years ago isn't always standard today, and that a 5' tub bought in '72 can be 1/4 in shorter than a 5' tub bought in 2005. Two panels of sheetrock and one of green board later, the tub is installed, is solid, and we're on our way to a leak free shower. We hope.
Thanks --
Amy