Historical Foundations: Brick in Aquatic Environments Through the Ages

Brick is one of humanity’s oldest manufactured building materials, with a lineage stretching back more than ten thousand years. Its primary role has always been terrestrial: walls, pavements, arches, and chimneys. Yet the idea of using brick in water—floating on the surface or resting on the seabed—is far from new. The Romans, masters of hydraulic engineering, used brick extensively in their aqueducts, harbor moles, and even the concrete cores of submerged breakwaters. The famed Portus complex at Ostia incorporated brick-faced concrete caissons that sat on the seafloor, proving that brick could withstand long-term saltwater exposure when combined with proper mortars and pozzolanic binders.

During the medieval period, brick-making techniques spread across Europe, and brick was used in canal locks, bridge piers, and tide mills. However, direct use in floating or submerged structures remained rare until the industrial era. The invention of Portland cement in the 19th century created a revolution: brick could now be bonded with truly hydraulic mortars, dramatically improving its water resistance. By the late 1800s, engineers began experimenting with brick-clad pontoons and submerged storage tanks, though these were still niche applications.

Today, the intersection of advanced material science and ecological design has revived interest in brick for aquatic construction. Modern bricks are no longer simple fired clay units—they are engineered composites, sometimes incorporating recycled materials, polymers, or specialized coatings. This evolution positions brick as a viable option for both floating platforms and submerged habitats, offering a blend of mass, durability, and aesthetic appeal that alternative materials like steel or concrete often struggle to match in specific contexts.

Material Science Innovations: Making Brick Water-Ready

The fundamental challenge of using brick in water is porosity. Traditional clay bricks can absorb up to 15–20% of their weight in water, leading to freeze-thaw damage, salt crystallization, and biological degradation. For submerged and floating applications, that level of permeability is unacceptable. Fortunately, recent breakthroughs have produced highly water-resistant brick variants suitable for aquatic engineering.

High-Performance Fired Clay Bricks

By raising kiln temperatures and using denser clays, manufacturers can create bricks with absorption rates below 5%. These severe weather (SW) grade bricks, already common in freeze-thaw zones, provide a starting point. Adding fluxes such as feldspar or nepheline syenite further vitrifies the body, closing capillaries. Some products, such as the Vitrified Clay Pipe industry’s extruded blocks, approach zero porosity. When used in submerged walls or ballast units, these bricks resist water ingress for decades.

Polymer-Impregnated and Coated Bricks

Another path involves impregnating fired bricks with penetrating sealers like silane-siloxane or epoxy resins. These treatments line the internal pore network, drastically reducing absorption without altering the brick’s appearance. Alternatively, factory-applied polymer coatings—such as polyurethane or polyurea—can create a seamless waterproof shell. For submerged applications, coatings also prevent biofouling when formulated with biocides or low-surface-energy additives.

Geopolymer and Recycled Brick Composites

Geopolymer bricks, made from industrial waste fly ash or slag activated with alkaline solutions, cure at ambient temperatures. They offer inherent chemical resistance and can be cast into complex shapes. Some formulations achieve water absorption below 2% and compressive strengths exceeding 60 MPa. Similarly, bricks incorporating crushed recycled glass or ceramics can achieve high density and low permeability. These sustainable options align with green building certifications and reduce the carbon footprint of aquatic projects.

Floating Structures: Bricks as Ballast and Architectural Elements

Floating construction has expanded from simple pontoons to entire neighborhoods, parks, and farms. Bricks play a dual role: as dead-weight ballast for stability and as finished architectural surfaces that resist water and weather.

Modular Floating Platforms with Brick Ballast

In modular floating systems, lightweight concrete or plastic hulls often lack sufficient mass to prevent tipping or drift. Filling internal chambers with dense brick units adds the needed weight without complex installation. For example, the Floating Gardens of Bengaluru use interlocking brick cassettes placed inside recycled plastic floats. The bricks, arranged in herringbone patterns, provide local ballast and also support soil for vegetation. This system allows rapid assembly and disassembly, and the bricks remain dry inside sealed compartments, avoiding long-term water exposure.

Brick-Clad Floating Homes

Architects designing floating residences increasingly turn to brick veneers to mimic land-based aesthetics. A Dutch project, Waterbuurt West in Amsterdam, features floating houses with brick facades mounted on lightweight steel frames above concrete hulls. The brick cladding is treated with a hydrophobic coating and backed by a drainage cavity, ensuring that rainwater and splash never saturate the brick body. This approach keeps the traditional look while meeting buoyancy and durability targets.

Floating Breakwaters and Wave Attenuators

Large floating breakwaters often employ scrap tires, concrete boxes, or steel pontoons. Brick offers an alternative: densely packed brick arrays inside perforated steel cages can create effective wave-damping structures. The bricks’ mass absorbs wave energy, while the cage confines them. Maintenance is straightforward—damaged bricks are replaced one by one. Early deployments in sheltered harbors of the Maldives have shown promising results, with brick-filled breakwaters lasting over 15 years with minimal corrosion.

Submerged Structures: Bricks Under Pressure

Underwater construction presents extreme challenges: high hydrostatic pressure, corrosion, biofouling, and limited access for repairs. Bricks have traditionally been excluded, but advances in grouting and reinforcement are changing that.

Submarine Habitats and Artificial Reefs

One emerging use is in artificial reefs and habitat modules. Bricks fired with controlled porosity can serve as substrate for coral larvae, while denser bricks form structural skeletons. The Reef Brick project off the coast of Florida uses interlocking brick blocks to create stable, multi-chambered habitats that resist currents. Over time, marine life colonizes the bricks, enhancing ecological value. The bricks themselves are made with a small percentage of oyster shell flour to encourage settlement.

Submerged Pipeline Supports and Tunnels

For pipelines crossing rivers or shallow seas, brick saddles and supports offer a low-cost alternative to concrete grout bags. Precast brick units, each weighing 5–10 kg, can be placed robotically or by divers to cradle pipes. The bricks’ rough texture provides grip, preventing sliding, and their durability exceeds that of sandbags. In the Yangtze River pipeline project, engineers used polymer-coated brick saddles for a 1.2 km crossing. After five years of monitoring, the bricks showed zero measurable erosion or cracking.

Underwater Masonry Walls and Dams

Traditional masonry techniques, adapted with modern waterproof mortars, are being revived for underwater structures. A notable example is the Brick Dam at Lake Evella, Japan, where a 10-meter-high wall was built using interlocking brick blocks set in a pozzolanic mortar. The entire structure was assembled in a cofferdam, then flooded. The bricks’ high compressive strength allowed a thinner wall profile than concrete, reducing material costs. The dam has operated for 12 years with only minor algal cleaning needed.

Advantages of Brick in Aquatic Construction

Choosing brick over steel, concrete, or polymers offers several distinct advantages, particularly when whole-life costs and environmental impact are considered.

  • Cost-Effectiveness: Bricks are manufactured globally using abundant raw materials. Local clay sources minimize transport emissions. Compared to marine-grade stainless steel or fiber-reinforced polymers, bricks can be 50–70% cheaper per unit of mass.
  • Ease of Manufacturing and Customization: Brick production requires relatively simple kilns and forming equipment. Custom shapes—dovetails, chamfers, hollow cores—can be achieved with minor die changes. Small batches are economically feasible, enabling project-specific designs.
  • Sustainability and Recyclability: Brick is made from natural clay and shale. Waste bricks can be crushed for aggregate or used as fill. Geopolymer bricks even sequester industrial byproducts. No toxic leaching occurs, unlike some treated timbers or plastics.
  • Fire Resistance: In floating buildings, fire is a critical hazard. Brick cladding provides a non-combustible barrier, slowing flame spread and protecting structural elements. This passive safety is a major advantage over wood or foam-plastic composites.
  • Aesthetic and Cultural Continuity: Brick’s warm tones and texture lend a sense of permanence and human scale to waterborne architecture. Homeowners and communities often prefer brick finishes for their familiarity and low maintenance.

Challenges and Mitigation Strategies

Despite these benefits, brick in aquatic environments faces real hurdles that require careful engineering.

Water Absorption and Freeze-Thaw Damage

Even low-absorption bricks will eventually absorb moisture if submerged continuously. In freezing climates, trapped water expands and cracks the brick. Mitigation involves selecting SW-grade bricks, applying hydrophobic impregnations, and ensuring that bricks in floating structures are kept above the waterline or encapsulated in waterproof membranes. For submerged bricks, avoid cycles of wetting and freezing—design for permanent submersion or use in non-freezing depths.

Biofouling

Submerged brick surfaces quickly become colonized by algae, barnacles, and mollusks. While this benefits artificial reefs, it adds weight and increases drag. In structural applications, regular cleaning or anti-fouling coatings are needed. Copper-based additives in brick bodies can deter settlement, but environmental regulations may restrict their use. A less toxic alternative is a surface treatment with silicone or fluoropolymer that makes adhesion difficult.

Structural Integrity Under Dynamic Forces

Waves, currents, and impacts from debris or vessels can dislodge bricks. Mortar joints, especially underwater, are vulnerable to scour. Using interlocking brick systems—such as those with male/female profiles—eliminates reliance on mortar. For submerged walls, reinforced concrete backing or grouted cells can create a composite structure that harnesses brick’s compressive strength while withstanding tension.

Salt Corrosion of Mortar

In saltwater, ordinary Portland cement mortar can degrade due to sulfate attack and chloride penetration. Replace with Calcium Aluminate Cement (CAC) or geopolymer mortars that resist chemical attack. Additionally, eliminate metallic reinforcement that might corrode—use fiber-reinforced plastic bars or purely brick-and-mortar mass structures.

Future Directions: Nanotechnology, 3D Printing, and Ecological Integration

The next decade will likely see brick’s role in aquatic structures expand through three converging trends.

Nanocoatings and Self-Healing Materials

Researchers are developing nanocoatings that repel water at the molecular level (superhydrophobic surfaces). A single-layer silica nanoparticle coating can reduce brick absorption to near zero while allowing the brick to “breathe.” Additionally, self-healing mortars containing encapsulated bacteria can precipitate calcite to seal cracks. When applied to brickwork in submerged tunnels, these mortars could autonomously repair damage from seismic events or differential settlement.

3D-Printed Brick Units

Additive manufacturing enables bricks with internal channels for ballast water, wiring, or fire suppression. A 3D-printed brick can include cable conduits, threads for bolting, and complex interlocking geometries that were impossible to mold. In floating structures, such bricks could form structural walls that also house mechanical systems. The cost of robotic printing is falling, making custom brick production viable for mid-scale projects.

Ecological Design and Blue-Green Infrastructure

Floating cities and submerged installations are increasingly designed as integrated ecosystems. Bricks can be manufactured with textured surfaces that encourage moss, algae, or even shellfish growth, turning structures into living reefs. The Oceanix Busan prototype, a floating city in South Korea, plans to use brick-based planters for hydroponic gardens and mangrove stabilization. By controlling porosity and chemistry, bricks become active components of the local environment, not just inert masses.

Case Studies: Lessons from the Water

Real-world examples illustrate both the potential and the pitfalls of brick in aquatic contexts.

Positive: Floating Brick Pavilion, Lake Zürich

In 2019, the ETH Zurich team constructed a temporary floating pavilion using standard SW-grade bricks stacked without mortar. The bricks were locked together with stainless steel rods, and the entire assembly sat on a submerged pontoon. The pavilion hosted concerts for six months, surviving storms and winter ice. Key success factors: all bricks were sealed with silane, the rods allowed easy disassembly, and the open structure prevented water trapping.

Negative: Submerged Brick Aquarium Tank Collapse

A public aquarium in Southeast Asia installed a brick-clad viewing tunnel in 2015. Within three years, mortar joints eroded due to improper curing, causing panels to dislodge. The tank had to be drained and rebuilt with reinforced concrete. The failure highlighted the need for stringent quality control of underwater mortars and the risk of relying on thin brick veneers in load-bearing submerged situations.

Ongoing: Brick Bridge Piers in the Venice Lagoon

The historic brick piers of Venice have stood for centuries, but rising sea levels now expose them to more frequent saltwater immersion. Conservators are experimenting with grout injection and surface coatings that restore strength without altering appearance. This work informs modern brick repair techniques for maritime heritage structures and demonstrates that brick can endure for centuries when properly maintained.

Conclusion: A Renaissance for Brick on the Water?

Brick is not a magic bullet for every aquatic challenge. Its weight, susceptibility to freeze-thaw damage, and the need for careful detailing limit its use. However, when paired with modern science—engineered coatings, interlocking forms, and sustainable binders—brick becomes a compelling material for floating and submerged construction. It offers a balance of cost, durability, aesthetics, and ecological compatibility that few other materials can match.

As climate change drives communities toward water-based living and infrastructure, the innovations detailed here will become increasingly relevant. Architects, engineers, and developers should not overlook brick as a 21st-century material for the world’s expanding wet frontiers. The old building block, born from earth and fire, is ready to meet water.

For further reading on water-resistant brick technologies, visit the Building Materials Research Institute and ScienceDirect’s resources on hydraulic mortars. Case studies on floating structures are available through the Delta Sync Floating Lab.