Thermalstrandbad Baden: Where stainless steel has been meeting thermal water and sand for 30 years

Thermal water, sulphur, thousands of square metres of sandy beach and around 225,000 visitors in a single season: the Thermalstrandbad Baden places particular demands on materials, cleaning and operations. For around 30 years, stainless steel pools from Berndorf Bäderbau have been part of this extraordinary, listed complex.

Opened in 1926, the Thermalstrandbad Baden Baths will celebrate their 100th anniversary in 2026. Historic architecture, thermal waters and a sandy beach covering some 3,700 m² continue to give the baths their distinctive character to this day.

The visitor figures also show that this character has lost none of its appeal. Around 225,000 people visited the thermal lido last season alone.

However, what looks like a holiday and a summer retreat for bathers presents particular challenges for the operators and technical staff. This is because sand, varying water qualities, sulphurous thermal water and intensive daily use place considerable demands on the materials used.

This is precisely where the story of Berndorf Bäderbau at the Baden swimming pool complex.

A refurbishment carried out in several stages

The collaboration with Berndorf Bäderbau began as early as 1995. The modernisation of the pool complex was deliberately carried out in stages.

During the first phase of refurbishment, from November 1995 to April 1996, the mineral pool and the two sulphur pools were rebuilt. This was followed, from November 1999 to April 2000, by the sports and diving pool, the multi-purpose pool and the children’s paddling pool. Finally, in 2004, the slide landing pool was added.

Over several years, this resulted in a stainless-steel pool complex with a total water surface area of around 2,876 m².

The largest pool is the 60-metre-long mineral pool with a water surface area of 930 m². These are complemented by, amongst other things, a 50-metre sports and diving pool, a multi-purpose pool just under 48 metres long, the children’s paddling pool, two sulphur pools and the slide landing pool.

Today, this means that the first pools refurbished by Berndorf Bäderbau have been in operation for around three decades.

Not all water poses the same challenges

One of the technical features of the thermal lido is the use of different grades of stainless steel. The composition of the pool water and the operating temperature are decisive factors in the choice of material. Depending on the pool water, special tests and specific analyses by our experts are required.

For the pool facilities in Baden, the materials 1.4404 and 1.4462 were used. The reason for this lies in the varying water qualities and compositions within a single bathing facility.

Whilst conventional swimming pools have different chemical conditions, the thermal beach pool also utilises mineral water and sulphurous thermal water. The sulphur pools, in particular, place increased demands on the material’s durability.

The 1.4404 grade is a tried-and-tested stainless steel for swimming pool facilities. With 1.4462, a high-alloy duplex steel is also available, which offers particularly high corrosion resistance.

The thermal beach pool thus clearly demonstrates that the choice of material should not be made on a one-size-fits-all basis. The decisive factor is always the conditions to which the material will be exposed throughout its entire service life.

Stainless steel meets listed buildings

In Baden, a particular challenge lay not only beneath the water’s surface.

The thermal lido, with its historic architecture, is a listed building. The modernisation project was therefore never simply a matter of posing a new pool complex with the existing lido. Rather, new technical solutions had to be integrated into a complex that had evolved over time.

It is precisely at this interface that another strength of stainless steel becomes apparent: The material can be individually shaped and adapted to existing geometries and architectural specifications.

This is particularly evident in the area of the sulphur pools. There, stainless steel meets historical and design elements made of stone and marble directly. Solutions for these material combinations were developed specifically by Berndorf Bäderbau for this project. (Cascades)

Such transitions require meticulous attention to structural detail. Different materials have different properties and must be joined together in such a way that function, watertightness, durability and design work in harmony over the long term.

The aim was not to alter the listed character of the thermal lido, but to utilise modern pool construction technology in such a way that the identity of the historic baths is preserved.

In this way, stainless steel does not become a foreign element within the existing structure, but rather part of its ongoing development.

Hygiene is a daily task

Sand differs significantly from many other types of debris found in swimming pools.

Whilst light materials can be carried across the water’s surface towards the overflow channel, grains of sand sink to the bottom of the pool due to their weight.

This means that what appears to be a minor feature of the lido becomes a daily consideration for cleaning and operations.

The pools are therefore cleaned every day during the season. In the case of the two sulphur pools, we go one step further: they are regularly drained completely, cleaned and then refilled. This ensures a particularly high standard of hygiene.

Particularly at a busy lido with a sandy beach, this consistent maintenance is an essential part of the operational concept.

And it is also evident to the eye.

The fact that stainless steel surfaces still look well-maintained and high-quality after decades is not solely down to the material itself. The combination of durable material, expert craftsmanship and consistent daily cleaning helps ensure that the pools have lost none of their appeal, even after many years.

A partnership that doesn’t end with the handover

What is remarkable about Baden is not only the length of time the facility has been in operation, but also the relationship that has endured beyond the initial construction phases.

Even decades after the first refurbishment works, there remains a close and personal relationship between the thermal lido and Berndorf Bäderbau.

Whenever questions arise or support is needed, it is only a short trip to Berndorf. The fact that Berndorf Bäderbau is practically ?on speed dial’ at the lido perhaps describes the collaboration more accurately than any formal term.

Berndorf staff are still regularly on site today. Over the years, a construction project has thus evolved into a partnership in which experience from day-to-day operations feeds back into the project and technical issues can be addressed jointly.

This continuity is of particular value, especially for a facility that has been in operation for decades and is constantly being further developed.

30 years of operation as a long-term test

When it comes to swimming pools, the quality of a solution is not determined on the day of opening.

What matters is how the materials and structures perform after ten, twenty or thirty years of daily use.

The swimming pool complex provides an exceptional example of this. Some of the stainless-steel pools built by Berndorf Bäderbau have now been exposed to the conditions of a heavily frequented outdoor pool for around three decades.

And these conditions are anything but ordinary: thermal water, sulphurous water, around 3,700 m² of sandy beach, intensive daily cleaning, high visitor numbers and seasonal outdoor pool operations all come together here.

Around 225,000 visitors in a single season make it clear that this is no mere theoretical long-term test. The pools are used day in, day out.

And that is precisely what makes this project so significant.

Thermal water as part of our identity

For centuries, Baden has been closely associated with its thermal springs. Today, the town boasts numerous active thermal springs and boreholes. Several million litres of sulphurous thermal water flow out every day.

The Marienquelle is of particular significance to the thermal lido, as it continues to supply the lido with thermal water to this day.

The two so-called ?Wandln’ are an institution in their own right. These small sulphur pools have been in existence since 1951. With water temperatures of around 34 to 36 °C, the focus here is not on competitive swimming, but on relaxing in the warm sulphur water.

It is precisely these different uses within a single facility that make the planning and choice of materials particularly challenging.

3,700 m² of sand right next to the swimming pool

The sandy beach is at least as extraordinary as the thermal water.

Around 3,700 m² of sand creates an almost Mediterranean beach atmosphere right in the heart of Baden. Even when the lido opened in 1926, large quantities of sand were transported to Baden.

For the lido, however, this unique feature means additional work.

After all, when hundreds of thousands of visitors move between the sandy beach and the swimming pools over the course of a season, sand inevitably finds its way towards the pool area.

This begins as soon as visitors enter the water. Showers and hygiene areas therefore do more than simply fulfil their traditional role of rinsing off dirt before swimming; they also help to minimise the amount of sand entering the pool area as much as possible.

Nevertheless, it cannot be prevented entirely.

If you build with stainless steel, you’re building to last for decades

The Thermalstrandbad Baden have been synonymous with summer, water and quality of life for 100 years.

For around 30 years, stainless steel from Berndorf Bäderbau has been part of this story.

Of course, thorough daily cleaning plays a key role in ensuring that the pools still look well-maintained today. However, maintenance alone can only preserve what has been designed and built to last.

Baden therefore demonstrates particularly impressively what durability in swimming pool construction actually means.

A pool must not only impress at its opening. It must accommodate hundreds of thousands of bathers, be cleaned daily, cope with varying water qualities and still function reliably after years and decades.

Anyone who builds a stainless-steel swimming pool is therefore not building for the first day. They are building for decades.

The pools at the Baden Thermalstrandbad show what this can look like after more than 30 years.