Most tubs use porcelain enamel (cast iron or steel) or acrylic or gelcoat on composites; refinishing adds epoxy or acrylic-urethane.
Shopping or troubleshooting a tub gets easier once you know the skin on the surface. That thin outer layer sets the shine, stain resistance, grip, and cleaning rules. Here’s a clear guide to the coatings you’ll meet, how they’re made, and how to care for each without wrecking the finish.
What Bathtubs Are Coated With: Materials And Layers
Factory tubs leave the line with one of a few common skins. Cast iron and steel carry a fired glass glaze called porcelain enamel. Acrylic shells are thermoformed sheets backed by fiberglass. Fiberglass shower-tub combos and many shower pans wear a sprayed polyester gelcoat. Cultured marble and many “stone resin” or “solid surface” units use a gelcoat skin too. Each route gives a hard shell, just by different chemistry and heat.
| Coating Type | What It Is | Where You’ll See It |
|---|---|---|
| Porcelain enamel | Glass fused to metal at high heat; glossy and chemically inert | Cast iron tubs, enameled steel tubs |
| Acrylic sheet | Thermoformed PMMA sheet; color runs through the sheet | Freestanding and alcove acrylic tubs, many spas |
| Polyester gelcoat | Pigmented resin sprayed in a mold, then backed by fiberglass | Fiberglass tubs, shower pans, cultured marble, stone resin |
| Refinish topcoats | Two-part epoxy or acrylic-urethane sprayed on old tubs | Reglazed tubs of any base material |
| Slip-resist patches | Textured acrylic or silica grit in clear resin | Factory safeguard zones or added during refinishing |
Porcelain enamel is a fired glass layer on cast iron or steel. The coating starts as frit and minerals, melts in a furnace, and bonds to the metal. The result resists heat, UV, and cleaners that would haze plastic skins. The Porcelain Enamel Institute describes it as a vitreous, inorganic layer fused above high temperatures. Learn more about porcelain enamel.
Acrylic tubs come from heat-molded sheets reinforced with fiberglass. Brands publish that combo in product literature. Kohler’s homeowner guide notes a high-gloss acrylic shell backed by fiberglass for strength.
Gelcoat is the colored spray layer you see on many composite baths. It’s a polyester or vinyl-ester resin loaded with pigment and additives. It sprays into a polished mold, cures to a hard film, then takes a fiberglass backup. The American Composites Manufacturers Association outlines those gelcoat basics and the need for controlled spray and cure. See ACMA on gelcoat.
What Tubs Are Coated With Today: Quick ID In The Bathroom
Not sure which shell you’ve got? A few light checks tell you fast. Work gently and pick a hidden spot for any test.
Weight And Sound
Cast iron is heavy and dull-sounding. Tap the rim with a plastic brush handle. A deep thud points to iron under glass. Thin steel rings a bit but still feels cool and rigid. Acrylic and gelcoat on fiberglass feel warmer and give a softer knock.
Magnet And Edge Clues
A fridge magnet sticks to steel. It won’t stick to cast iron through thick enamel, but a strong magnet can grab around hardware where the metal is close to the surface. Look at the drain cutout: a thin metal lip hints at steel; a thick wall with glassy edges hints at iron. Acrylic shows a solid color through the cut, not a glass glaze.
Surface Feel
Porcelain enamel feels glass-hard and slick. Acrylic feels slightly warmer, with a softer “drag” under a fingertip. Gelcoat can show faint mold texture or a slightly waxy feel when new. None of these should feel gritty unless a slip zone is molded in.
Factory Coatings, Layer By Layer
Porcelain Enamel On Cast Iron Or Steel
Think of a glass glaze on cookware. The tub body takes a base coat and a cover coat of glassy frit, then gets fired. The bond is at the molecular level, which is why the glaze resists staining and UV fade. Brands promote the chip and scorch resistance that comes with that fired shell. Kohler outlines its enameled cast iron, and the PEI describes the vitreous nature of the layer.
Acrylic Sheet Over Fiberglass
Here a PMMA sheet is heated, vacuum-formed over a mold, then backed with fiberglass for stiffness. The color goes through the sheet, so light scratches often buff out. Product manuals and spec sheets call out “acrylic reinforced with fiberglass.”
Gelcoat Over Composites
Gelcoat brings color and gloss. It sprays a controlled thickness into the mold. After cure, glass fiber and resin form the structure behind it. Many “cultured marble” or “stone resin” baths use this skin. ACMA notes the resin family, pigments, and spray control that keep the film flat and strong.
Refinishing Coatings: What Re-Skins Old Tubs
When a pro reglazes a tired tub, the new shell isn’t porcelain enamel. Shops spray catalyzed coatings that cure at room temp. Two groups dominate: two-part epoxies and two-component acrylic-urethanes. Kits sold at retail tend to be epoxy. Trade systems often use an epoxy primer under an acrylic-urethane topcoat for better gloss hold and yellowing resistance. See a common epoxy kit.
What To Expect From A Refinish Layer
Sprayed in thin films, these coatings can look great and buy years. They are softer than fired glass, so they scratch and stain sooner under harsh use, but careful cleaning extends life. Cure time matters; plan days with light use while the film hardens through.
Caring For Each Coating Without Guesswork
Good care starts with non-abrasive tools, gentle chemistry, and rinse-and-dry habits. Brand care pages give clear do’s and don’ts. Kohler outlines acrylic and gelcoat cleaning, and a separate page covers cast iron tub care.
| Coating | Safe Cleaners & Tools | Avoid |
|---|---|---|
| Porcelain enamel | Soft sponge; mild dish soap; diluted vinegar on soap scum | Steel wool; paint strippers; drain openers on the surface |
| Acrylic sheet | Microfiber; dish soap; specialty acrylic bath cleaner | Powdered abrasives; acetone; strong ammonia |
| Gelcoat | Non-scratch pad; pH-neutral bath cleaner | Abrasive powders; harsh solvents; stiff brushes |
| Refinish coat | Soft cloth; mild, non-chlorinated cleaner; squeegee after use | Bleach soaks; bathmats with suction cups; colored shampoos left to sit |
Pros, Trade-Offs, And Fit For Use
Porcelain Enamel
Strengths: hard glass feel, heat tolerance, long color life, wide cleaner range. Trade-offs: heavy body, chipped glaze needs pro help, cooler touch on skin. Great pick for longevity and a classic look.
Acrylic Sheet
Strengths: lighter weight, many shapes, warm touch, easy field repair for light scuffs. Trade-offs: reacts badly to harsh solvents, scuffs sooner under gritty use, needs gentle cleaners. A smart match for remodels where weight and access matter.
Gelcoat Composites
Strengths: crisp molded detail, rigid when backed well, repairable with gelcoat paste, broad color range. Trade-offs: needs gentle chemistry, can craze or chalk if cleaned harshly or sun-baked. Works well for shower bases and large one-piece units.
Refinishing Layers
Strengths: fast facelift, no demo, lower cost than a new tub, color change on demand. Trade-offs: softer film, strict cleaner list, cure time, and a finite life. Best for rentals, flips, or when tile and plumbing stay put.
Care Playbook You Can Use Today
Daily
Rinse the shell, pull water down with a squeegee, and dry the corners. This prevents soap scum and hard-water spots on any finish.
Weekly
Use a soft sponge with a mild bath cleaner. Work from the rim down. Rinse and dry. For enamel, a bit of diluted white vinegar helps with mineral film. For acrylic or gelcoat, stay with pH-neutral cleaners made for plastic skins. See cast iron cleaning steps.
Seasonal
Wax acrylic or gelcoat with a non-color carnauba wax made for plastics. Skip wax on porcelain enamel. Check caulk edges and drain seals while you’re there.
Repair Basics By Coating Type
Porcelain Enamel Chips
Small chips can take a porcelain repair kit