How it is made

How a steel enamel bath is made: deep drawing of sheet metal and enamel fired at 850 °C

A steel enamel bath is made from a single steel sheet, which is shaped into the bath form by a press. Holes for drainage and overflow are cut into the mould, handles are welded on, and enamel is sprayed – finely ground glass mixed with water. At around 850 °C, the enamel melts and bonds with the steel. We describe the production according to the German manufacturers Kaldewei and Bette.

Prepared by: TGB Kúpeľne team, bathroom showroom in Senec since 1991updated 9. 11. 20265 min read

Illustrative image: Steel bath shells on the production line before enamelling

A steel enamel bath combines two materials: steel, which provides shape and strength, and enamel – a layer of glass fired onto the surface. It is produced on pressing and enamelling lines. We describe the process according to manufacturers Kaldewei from Ahlenu and Bette from Delbrück. How to choose a bath based on material and size can be found in the article Bath for the bathroom: how to choose.

Summary of steps

Enamel: glass made from borax, feldspar and quartz

Enamel is essentially glass. Kaldewei states that the raw materials are borax, feldspar, quartz and soda. The mixture is melted in rotary kilns at a temperature of around 1,300 °C. The molten material is cooled in cold water and breaks down into small glass grains – frit. This is then mixed with water, additives and pigments into an enamel slurry that can be sprayed. Bette also prepares its enamel emulsion in-house.

Steel and deep drawing

The bath is made from a single sheet of steel. Kaldewei uses micro-alloyed steel with titanium and shapes the sheet on a pressing line with a force of up to 1,200 tons. In deep drawing, the press pushes the flat sheet into a mould and stretches it downwards – the bath thus has no weld or joint. Bette uses its own drawing tools and states that the edges of the bath are turned downwards.

Holes, strips and handles

Holes for the drain and overflow are cut into the mould – partially automatically at Kaldewei. Then, grounding strips, transport strips and handles for the legs are welded on. Holes for handles, taps or hydromassage jets are drilled by Kaldewei using lasers according to order. Everything is done before enamelling, so handles or hydromassage must be selected when ordering the bath.

Enamelling and firing at 850 °C

At Kaldewei, robots spray a base layer of enamel onto the moulds. This is fired in U-shaped kilns at a temperature of around 850 °C – the enamel melts and bonds with the steel into one unit. Then follows the top layer, which gives the surface its final appearance, smoothness and durability. In its brochure, Kaldewei states that the enamel is fired at 850 to 900 °C and for its steel enamel, a thickness of 3.5 mm.

Bette dries and fires the products in the oven at a temperature above 850 °C after applying the enamel. According to the manufacturer, three very thin layers of enamel are applied, which are fired twice. Three layers of enamel are also mentioned for its steel baths by Jika.

Inspection and standards

Every Kaldewei product undergoes quality control and is sold only after that. Production is serial: Kaldewei produces in Ahlen up to 8,000 baths and shower trays daily, while Bette produces about 2,000 products daily in its factory. The requirements for baths for households are set by the European standard EN 14516.

Can enamel be repaired?

A small chipped area can be covered with a repair kit for enamelled baths – such kits are commonly sold. However, this is not fired enamel. Bette warns in its repair instructions that new enamelling would require the bath to be removed and fired at high temperature in production. When enamel is damaged, it is therefore a matter of whether a cosmetic repair is sufficient or if a new bath is better.

What this means when choosing

• Surface – enamel is hard and scratch-resistant. However, without sound insulation, a steel bath is noisier when filling and cools down faster, as mentioned in the article Bath for the bathroom.
• Weight – the Kaldewei Saniform Plus steel bath 170 × 75 cm weighs about 50 kg according to vendor data, while the Polysan Marlene acrylic bath 170 × 80 cm weighs 27.3 kg according to the manufacturer.
• Holes for handles and hydromassage are made before enamelling – select them when ordering. We describe hydromassage baths in the article Hydromassage bath.
• Grounding strip is welded from the factory – an electrician will connect it during installation according to applicable regulations.
• Dimension check before ordering – see Dimensions of the bath.

How a laminate bath is made and how it differs from an acrylic one is described in the article How a laminate bath is made.

Sources: Kaldewei – Inside Kaldewei: the birth of the bath; Kaldewei – Saniform brochure (firing enamel, thickness); Hospitality Interiors – Kaldewei in Ahlen; Bette – BetteFactory plant; Bette at the ISH fair; Bette – repair instructions; Jika – catalogue; Czech buildings – bath renovation; QS Supplies – Kaldewei Saniform Plus (weight); Polysan – Marlene, technical sheet; EN 14516; our article Bath for the bathroom: how to choose.

Terms in the glossary: Overflow · Hydromassage bath · Acrylic bath