How to Figure out What Your Bathtub Is Made Of

Some things, like bathtubs, are installed for use for the long haul, and sometimes, they can last decades. Maybe you've discovered this by moving into a new home; you now have a tub that's seen better days, and you wonder if you should replace it. It depends on the tub material, and if you're not sure, you can figure out what your bathtub is made of.

What your tub is made of can give you an idea of how much load your floor is carrying. Some cast iron tubs can weigh hundreds of pounds. On the other hand, it may help clarify how far you should go with your bathroom renovations. If it's a fiberglass tub, it might be well past half of its life since they're expected to begin deteriorating within five years of installation.

Fiberglass is slated for a 10- to 15-year life span, says Marines Plumbing, but steel or cast iron can last decades. Tubs can be reglazed for cosmetic issues, and glazing can last a decade or more for about $200 to $650, according to ​Today​. Tub refinishing companies say just about any tub can be repaired and reglazed, but it's not always money well spent.

Acrylic lasts a little longer than fiberglass, but both have similar characteristics. If you can push in on the side of the tub and there's some give, then it's fiberglass or acrylic. Cracks and scratches are common for both fiberglass and acrylic tubs, whereas chips will usually indicate some kind of metal tub.

Fiberglass tubs are also notorious for having color fading on the bottom over time, so if you see that the bottom of the tub is discoloring versus the walls, that's a good indicator.

If your tub has no give at all, then it's steel or cast iron. Hold a magnet up to the tub; does it attract? If it's magnetic, then it's an enameled surface, but if it's not magnetic, it's porcelain. Each of these surfaces can be easily chipped with heavy impacts or if the tub has been cleaned too often with abrasive cleaners, which weakens the surface. If you need your porcelain tub to shine again, skip the abrasives and try using a gentler cleaning regimen.

If you have any chips on the tub's surface, that's generally an indicator of being a metal tub, and it's a good spot for testing with a magnet. Check for signs of rust just in case.

If you have a surround or casing that can be removed, you can investigate further. Cast iron tubs are heavy — sometimes hundreds of pounds — and they'll often have additional supports beneath the tub. Sometimes, you can see this under the flooring if there's a basement or crawlspace under the tub.

Once you know what your tub is made of, you can decide how to go about dealing with it. Reglazing is a strong possibility but so are bathtub liners. Both are more affordable in the short term than getting a new tub installed would be, but if it's an older fiberglass or acrylic tub, you might be throwing good money after bad.