Cast Iron or Fiberglass Tub?

by Jane VanOsdol on April 29, 2011

Is it time to replace your tub or shower? If so, you may be torn between your choices. Should you go with a cast iron fixture, or should you instead choose a fiberglass unit for your bathroom?  Naturally, both choices have their good points and bad. Let’s consider the differences.

Cast Iron

When most people think of a cast iron tub, they picture the classic claw-foot tub, which is one example of a cast iron tub. Cast iron plumbing fixtures are known for their durability and strength. Cast iron simply does not flex. Cast iron fixtures have a thick enamel coating that is fused to the cast iron in high temperature ovens (at temperatures over 1,700°F). During this process the enamel becomes extremely hard, close to the hardness of glass. However, as anyone who has an enamel kitchen sink knows, enamel scratches and it can chip. Be that as it may, a cast iron tub is a good investment because while it may show signs of wear and it may chip, rarely does it crack.

The chips that may develop, especially if your drop something heavy in the tub, can be beautifully repaired in a bathtub refinishing process. As far as maintenance goes, be sure when you are cleaning the tub that you use a non-abrasive cleaning product, because abrasives can scratch even a cast iron tub.

Fiberglass/ Acrylic Tubs

When it comes to “plastic” tubs, there are three main types:  gel-coated fiberglass, acrylic reinforced with fiberglass and acrylic backed with structural composite. You’ll find in this field many different manufacturers with a multitude of tub and shower styles. A main drawback to these fixtures is that traditionally they can flex quite a bit, and they are prone to scratches and cracking.

When constructed with quality materials and manufactured correctly, the gel-coated fiberglass fixtures can be very hard, albeit not as hard as enameled cast iron. If they are damaged or scratched, a fiberglass tub repair usually is a successful fix, being permanent and nearly invisible.

Acrylic units are made from large sheets of acrylic plastic, which are heated so that they are moldable. They are then stretched around a mold into the shape of a tub or shower. Some spots become thin during the stretching process, especially in the corners. The floors also tend to flex, although the acrylic fixtures that are backed with structural composite have addressed this problem. Fixes to the acrylic units aren’t always successful.


As with anything, proper care will help maintain your tub or shower fixture. Regular cleaning will help maintain the surface and keep soap scum from building up. Avoid abrasive cleansers so that you don’t scratch the fixture. You can use the same cleaning products on the plastic tubs that you would use on a new car. Ask the Builder Tim Carter recommends that once a month you take 15 minutes and apply a high quality spray car wax to the wall surfaces of your acrylic tub or shower (never the floor!).  Buff the wax out, and your fixture will look as shiny as new.

Overall, when deciding between a cast iron or fiberglass fixture, choose the model you feel best fits your budget and your style.

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