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Technology

The material comes from boatbuilding and offshore.

Glass-fibre reinforced composite has been used in boat hulls for some seventy years and in subsea structures on the continental shelf for decades. Seawater is an aggressive environment — salts, micro-organisms and fouling degrade most building materials over time. A boat hull stands in constant UV radiation as well. Composite handles both, and a swimming pool is a milder environment than either.

Arendal Sjøbad, the floating swimming facility in Arendal guest harbour, with swimmers in the pool

Material

Glass-fibre reinforced composite

Build-up

Sandwich with insulating core

Track record

~70 years in boat hulls

Floating facilities

Vacuum-infused in one operation

Land-based facilities

Panel assembly with membrane

Surface

Part of the laminate — no tiles

The construction

Stiffness without weight.

A sandwich construction is two thin, stiff laminate skins held apart by a light core. The principle is the same as in an I-beam: the strength lies in the distance between the flanges, not in the mass between them.

Layer 01

Outer laminate

Glass fibre in a cured plastic matrix. It carries tensile and compressive loads and forms the finished surface at the same time — there is no coating that can come loose.

Layer 02

Core

A light core material made from recycled plastic. It holds the skins apart, transfers shear between them, and insulates against heat loss from the water — one component with three functions.

Layer 03

Inner laminate

The mirror image of the outer. Bending stiffness grows with the square of the distance between the skins, which is why a thick, light core gives a great deal of stiffness for very little weight.

Everything else hangs on that weight saving. It is why a floating facility floats with margin and can be towed, and why a land-based facility can rest on asphalt or gravel instead of a foundation sized for the weight of concrete.

The core also does something a steel shell cannot: it insulates. Steel conducts heat, and a heated steel pool loses heat through the whole shell all year. The sandwich construction is load-bearing and insulating in the same component — and for an outdoor facility that has to be kept warm, that is an operating cost running every day for fifty years.

Service life

Pools fail in ways composite cannot fail.

Over the past ten to fifteen years, steel pools have largely taken over from concrete and tiles. That is a real improvement — prefabricated, faster to install and without sealant lines that let go. But the question is the same for both: how does the structure stand after thirty years in chlorinated water?

Concrete — the old way

Reinforcement corrosion

Chlorides penetrate the concrete and reach the reinforcement. The rust expands, the concrete spalls from within, and the damage accelerates once it has started. This is the classic failure mechanism in older pools.

Steel — today's standard

Welds, crevices and heat loss

Stainless steel is a large step up from tiles. But chlorides attack at weld zones and in crevices where water stands still and concentration builds. And steel conducts heat well. In a heated outdoor facility the shell is itself a heat leak.

Composite

Neither of them

No reinforcement to rust, no cement paste to carbonate, no welds to attack. The surface is part of the laminate, not a layer bonded on top. And the core insulates rather than conducts — the structure holds the heat instead of giving it away.

The track record is not theoretical. Glass-fibre boats have been produced since the 1950s, and hulls from the 1960s and 70s are still in service in salt water — after sixty summers of UV radiation that degrades most other materials outdoors. For an outdoor swimming facility, UV resistance matters exactly as much as resistance to the water.

Production

Same material, two methods.

How the structure is put together depends on whether the facility is to float or stand on land. The material and the water treatment principles are the same.

Vacuum infusion — floating

Fibre and core are laid up dry in a mould. The entire structure is infused with resin under vacuum in one continuous operation and cures as a single piece. No cold joints, no sealant lines.

Bonding under pressure — land-based

The sandwich elements are bonded under pressure and vacuum, so that skin and core achieve full, even adhesion across the whole surface. The panels are assembled on site, and a continuous membrane is laid over every wetted surface.

Factory rather than building site

Both methods move the critical work indoors, with machined precision and documented quality per unit. A concrete pool is cast outdoors, where season and weather feed straight into the result.

Water treatment per basin

If the water surface is divided into several basins, each gets its own water treatment system. That is the precondition for training, teaching and therapy basins holding different temperatures at the same time.

Climate footprint

Counted across the service life, not per kilo.

Thermoset plastic has high emissions per kilo taken in isolation. But the calculation is not settled there. It is settled by how many kilos actually go into the structure, how long it lasts, and what has to be replaced along the way.

A composite pool uses a fraction of the material mass of an equivalent facility in concrete. The core material is made from recycled plastic. Transport weight follows mass. The surface is part of the laminate and is not replaced. And because the facility stands outdoors, the emissions tied to erecting and operating a building envelope disappear entirely.

If the figure has to be documented for a procurement, the calculation is made in the pre-project for the specific facility.