What should you know before buying a cast iron bathtub?

How much does a cast iron bathtub weigh?

Typically 250 to 500 lb empty. Kohler's K-715 Villager 60 x 30-1/4 in alcove tub lists 316 lb, a 33 gal water capacity and a minimum floor load of 49 lb/ft². Kohler's store guide says cast iron tubs weigh 300–400+ lb, against 100–150 lb for acrylic, and that cabinets and floors must support them.

Solid stone is a heavier class. Our solid stone tubs run about 1,100–2,500 lb empty, and a typical 67 x 31 x 22 in marble oval is about 1,150 lb empty and about 170 lb/ft² on its footprint, against 40 lb/ft² for a typical residential floor live load. See the stone bathtub weight guide. Floor decisions belong to a structural engineer.

Does a cast iron tub keep water warm?

Kohler's store guide says cast iron holds heat better than any other tub material, so bathwater stays warm noticeably longer. That is the retailer's statement on Kohler's behalf and not a test result. Engineering ToolBox lists cast iron at about 52 W/m·K, which is far higher than acrylic at 0.2, so the benefit comes from the mass of metal rather than from insulation.

Kohler's guide lists acrylic as warm to the touch, a point it does not claim for cast iron. Marble conducts heat at 2.08–2.94 W/m·K, much lower than iron. Our warm water guide explains how thick stone behaves.

How do you care for an enamel cast iron tub?

Clean it gently and avoid heavy impacts. Kohler's store guide calls the enamel extremely hard but says it can chip if struck sharply by heavy objects such as cast iron cookware, and that touch-up kits can repair chips. Kohler's care guidance for its baths is to test a cleaner on an inconspicuous area, wipe and rinse completely, and not let cleaners soak on the surface.

• Wipe the surface after bathing and rinse cleaner off right away.
• Avoid dropping heavy objects into the tub.
• Repair chips promptly with a manufacturer touch-up kit.
• Use the cleaner your tub's maker recommends.

Stone needs its own care. Marble etches in acid and benefits from sealing. See the care guide.

How does a cast iron tub compare with an acrylic tub?

Cast iron is heavier, harder-wearing and more costly. Acrylic is light, warm to the touch and easier to shape. Kohler's spec sheets for two 60 in alcove tubs show the gap in weight, and Kohler's store guide supplies the longevity and cost claims.

Acrylic also suits shapes and jets that iron cannot, and, per the Kohler guide, needs no floor reinforcement.

How does a cast iron tub compare with a solid stone tub?

Cast iron wins on weight, on price and on a wide range of enamel colors. A 316 lb alcove tub is a manageable lift next to a 1,100–2,500 lb stone tub, and a K-715 lists near $808–$1,078 while published solid stone tubs run about $13,999–$37,000. Cast iron is also a familiar, repairable surface.

Stone wins when you want a tub carved from one natural block, with no coating that can chip, and with the character of the stone itself. A stone tub has no enamel layer, so its surface and body are the same material. Kohler says its enamel resists stains, while marble can etch in acids. Neither is better outright. They suit different houses.

Read stone vs acrylic and stone resin vs solid stone for the nearest comparisons. Pietra Fonte makes made-to-order stone bathtubs, and every quote gives exact dimensions and weight.