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Question DetailsAsked on 5/29/2012

Fiberglass or Cast Iron tub in remodel?

My tile installer is recommending a fiberglass tub in my bath remodel where he will be doing tile. The guy at Home Depot recommends cast iron. Which is better for rental property? Would I need an additional support joist for the weight of the cast iron?

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5 Answers

Voted Best Answer

What is the floor structure under the tub? Concrete will provide the best support but I've placed cast iron tubs on wooden joists before as well. They'll likely have to be beefed up to hold the extra weight, especially if the old tub was fiberglass. 30" cast iron tubs can weight 350-400 lbs. Fiberglass is about 60-75 typically. The water weight and occupant is basically the same.

If set properly I'd go with the fiberglass tub in a rental and usually do for my customers. They are cheaper and the nature of the beast with rentals is eventually it will get damaged. If set in a morter bed and proper framing a fiberglass tub will last through many tenants. Also, it's a bit more chip resistant (well, the good ones are). Cast iron tubs can chip even from a can of shaving cream being dropped. You can have both recoated for about the same amount of money. In the end it's about how much you want to spend. If it's an upscale rental where tenants might expect cast iron, pay the extra money for it to be installed right. If it's for the average middle class family you're fine with the fiberglass tub. Both should be set on adequate framing in a morter bed to help distribute the weight and reinforce the bottom.

Todd Shell
Todd's Home Services

Answered 8 years ago by Todd's Home Services


Porcelain over cast iron is the strongest tub out there and they're made to last. However, as with any surface, the porcelain surface can chip if you drop something in/on it.

Are you removing an existing tub?


Answered 8 years ago by sharprefinishing


If you have structurally sound 2x8 or 2x10 joists with a 3/4 wood or plywood floor you can reasonably expect to be able to install a cast iron bathtub. When properly framed, a floor is designed to be able to handle the load of a filled bathtub with no problem.

A cast iron bathtub is, generally speaking, the most durable bathtub. However, once the porcelin surface is chipped the damage is for all practical purposes permanent. Cast iron bathtubs can be "resurfaced" and around here (Twin Cities, Minnesota) the resurfacing companies will provide a 5 year warranty to repair any damage to the finish. The problem is that the refinish is essentially a paint job. I've seen nicks appear VERY easily on resurfaced Cast iron tubs.

Modern cast iron tubs tend to have shallower water levels. The overflow level on a Kohler Villager is less than 9". A Kohler Mendota, it's less than 12".

Fiberglass tubs are not as durable as cast iron. However, fiberglass tubs can be repaired. The repairs can be considered permanent for the most part.

Fiberglass tubs are frequently deeper than cast iron tubs. I know of several that have 15" to the overflow.

I have a rental property and I installed a cast iron tub. (Kohler Mendota). I'm a plumber and could install any tub I want. I think Kohler has the best porcelin finish available for tubs.

The trick is to get tenants that will not be hard on the rental unit.

Answered 8 years ago by Geno Gardner


Cast iron! If you plan to stay there and grow old ,make sure backing is put in the wall for the future for grab bars and then the seat you put in the tub will not break out the bottom of the tub like fiberglass will!

Answered 8 years ago by wmadix


I think the individual asking the question, is missing a VERY important material...ACRYLIC!

Acrylic is NOT fiberglass. Acrylic is the number one material used by all major (and minor) fixture manufacturers for bath tubs, with the exception of steel tubs.

Acrylic is a glossy plastic, like fiberglass, however it is different when you're standing, or sitting on it. Glossy acrylic, has traction against the bottom of your foot, (or tush) even when wet.

it's considerably less expensive that Cast Iron, available in all price ranges, low/medium/high, will offer every possible option, regardless of size, and will provide more selection, that fiberglass, and cast iron, combined.

Unless you're going for a slipper tub, go acrylic.

Answered 6 years ago by Guest_9004778


One thing on the comment about deeper tubs - some come up to 18" deep now, but if you are putting in a tub with deeper water level (from bottom to overflow) than the original in that location, I would have a structural engineer advise on whether your flooring need beefing up. Many residential floors are designed for maximum of 20 or 30 psf (pounds per square foot) - an 18' deep cast iron tub would be around 100 psf - an invitation to possible unfortunate consequences. Normally a modern construction floor (with 3/4" subflooring) would distribute normal bathtub loading (say maybe 50 psf range if 9" water depth) enough to avoid a problem, but as the floor joist get older and maybe compromised by water seepage is where you commonly get surprises - though I have seen and heard of cases where someone put a very heavy Victorian tub into a bathroom and the owner and the downstairs neighbors got a VERY unpleasant surprise when it was first filled.

Answered 4 years ago by LCD

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