In Alsfeld, a historic building has been given a new lease on life: Villa Raab was renovated under the direction of the architectural firm Weppler-Jungermann. Building systems manufacturer SAKRET played a crucial role in the project.

Exemplary Renovation of Villa Raab in Alsfeld in the Spirit of Historic Preservation

The stately villa, built in the French palace style during the Gründerzeit era, was to undergo a comprehensive renovation in accordance with historic preservation guidelines after years of standing vacant and beginning to fall into disrepair—in retrospect, an extraordinarily successful project by the entrepreneurial couple Ralf and Tanja Bohn. Under the direction of the architectural firm Weppler-Jungermann, Sachs Baudekoration from Lauterbach, Hesse, and the historic preservation authorities, partners from a wide range of fields were coordinated: SAKRET as the system manufacturer of the necessary building materials and a partner for plastering, painting, and tiling work, Scheerschmidt and Schneider (Stadtallendorf) for the tiling work, and the specialty firms Golem (Sieversdorf) and Replicata from Freiburg recreated the historic décor and produced reproductions of historical originals.

The interplay of magnificent Neo-Baroque with the then-modern Art Nouveau style can be seen and felt everywhere, both inside and out. Photo: © sakret.de

To repair and replace historic tiles both indoors and outdoors, they had to be crafted using period-appropriate materials and expertly installed. These tiles had to be able to withstand extreme temperature fluctuations while also being waterproof, frost-resistant, and highly durable. Photo: © sakret.de

Valuable historic tiles, including some from Villeroy + Boch, in the hallways and stairwells were almost completely preserved. Photo: © sakret.de

The round arches of the vaulted ceiling (approx. 120 cm in span) were plastered with SAKRET MAP-SL+ machine-applied exterior plaster. This material could be applied and troweled to the required thickness of up to 5 cm in a single coat. In the basement rooms, SAKRET KIP // KPM I lime interior plaster was also used.

After standing vacant for years and beginning to fall into disrepair, this architectural gem was comprehensively restored true to its original form by a team of selected experts and specialists. Photo: © sakret.de

A Successful Team Effort

The renovation of Villa Raab can now be considered a prime example of the synergy between dedicated contractors and rigorous historic preservation standards. Lead architect Jochen Weppler also spoke highly of the success of this collaboration: “A truly successful team effort that allowed us to meet even the most complex requirements of historic preservation in the best possible way.”

Photo: © sakret.de

The shared goal: to restore the property to its original condition

The property’s special value lay in its numerous original interior and exterior details. These included, for example, the magnificent exterior facades with their rich ornamentation of decorative elements and moldings, as well as the stucco cornices and friezes in the main rooms. The valuable, historic tile flooring in the hallways and stairwells was also completely preserved, with only a few missing sections. To meet the requirements for materials in the areas of plastering and tile installation, SAKRET was able to offer system-based product solutions that—in accordance with historic preservation regulations—ensure a long service life. These included, for example, materials such as felt plaster, lime interior plaster, and marble-based fine-finish putty.

Fortunately, the villa remained largely in its original condition, enabling a faithful reconstruction of the house with its numerous moldings, stucco cornices, and friezes. Photo © sakret.de

The Exterior Work

The overall condition of the building required extensive preparatory work: Cracks running through parts of the masonry had to be grouted, and many of the stone balcony railings had to be removed for restoration. After cleaning the entire facade, it was plastered with SAKRET KAM adhesive and reinforcing mortar.

Next, SAKRET KAM felt plaster (0.8 mm grain size) was applied as a decorative topcoat. For smooth surfaces such as building corners, walls, window surrounds, etc., SAKRET MFS Fine Marble Filler was used. This made it possible to fill unevenness of up to 1 cm in a single pass.

The property’s special value lies in its numerous interior and exterior details that have been preserved in their original state. For example, the magnificent exterior facades with their rich ornamentation. Photo copyright: © sakret.de

The Renovation of the Interior

Inside the villa, the entire wall plaster had to be removed due to moisture that had penetrated the structure over decades.
SAKRET KIP lime interior plaster—awarded the Blue Angel label for its environmental compatibility—was used as the base coat. To plaster the old brick walls, SAKRET KIP was applied in two passes, wet-on-wet, using the G4 plastering machine, to a layer thickness of up to 7 cm.
After the drying period, the wall surfaces were completely finished with SAKRET KIP Multi Interior Lime Plaster KPM I, 6 mm thick, with an alkali-resistant SAKRET mesh embedded within to prevent cracking. The final coat was applied using SAKRET Edelfilz Plaster EFP 0.5 mm.

The interior spaces required extensive preparation and planning, as not only did the wall and ceiling designs need to be restored true to the original, but new installation and piping systems also had to be installed to meet modern standards. Photo: © sakret.de

The special value of the property also lay in the numerous design details on the walls and ceilings. These were mostly removed and then reinstalled after restoration. Photo: © sakret.de

Details on Tile Work

SAKRET Universal Primer UG and SAKRET Special Primer SG were used as a primer on mineral plasters, concrete, and cement screed, as well as for priming cement-based building boards. For waterproofing damp and wet areas, SAKRET Alternative Waterproofing AA was recommended as a tested system component.
SAKRET Flex Tile Adhesive FFKs and the multifunctional SAKRET Euroflex EF flexible mortar enabled efficient tile installation. Finally, the fast-setting SAKRET Flex Grout FFM was used to grout the tiles.

In Alsfeld, a historic building has been given a new lease on life: Under the direction of the architectural firm Weppler-Jungermann, Villa Raab was renovated. System manufacturer SAKRET played a decisive role in the project.

Gabions are among the most versatile structural elements in landscaping: wire mesh baskets filled with natural stone or other bulk materials are used to create retaining walls, fences, noise barriers, and decorative room dividers. Anyone who chooses to set gabions in concrete is departing from the classic logic of a flexible, drainable gabion system and is consciously opting for a more dimensionally stable, durable connection to the subgrade or between individual components. This decision has far-reaching consequences for load-bearing capacity, drainage, reparability, and service life, and it must be technically justified.

• What it means to encase gabions in concrete and when it makes sense
• How to properly construct a gabion structure set in concrete
• What concrete grades, foundations, and fasteners are used
• What structural and drainage requirements must be considered
• Where concrete-encased gabions are used in the context of open space and urban planning
• What advantages they offer over unfounded or simply placed gabion systems
• What typical errors occur during planning and construction and how to avoid them
• How to assess maintenance, repair, and deconstruction of gabions encased in concrete

What it means to embed gabions in concrete: Definition and distinction

A gabion (from the Italian “gabbione,” meaning “large cage”) is a wire mesh basket enclosed on all sides that is filled with stones or other bulk materials. In traditional applications, gabion baskets are placed on a compacted bed of gravel or crushed stone without mortar and connected to one another using binding wires or clips. The system’s strength lies in its flexibility: it can compensate for settlement, is permeable to water, and can, in principle, be dismantled. In contrast, embedding gabions in concrete refers to the deliberate integration of gabion baskets or entire gabion walls into a concrete foundation, the grouting of connection points with concrete or mortar, and, in certain cases, the partial filling of gabion baskets with concrete instead of loose fill material.

This distinction is important because the two approaches result in different system properties. A gabion wall set on a gravel bed is a flexible, gravity-retaining structure that derives its stability from its own weight and friction. A gabion structure encased in concrete, on the other hand, is rigidly connected to the subgrade and behaves structurally more like a conventional retaining wall made of concrete or masonry. This rigidity is expressly desired in certain situations, such as for high support heights, structures subject to traffic loads, or sites with uneven ground that are prone to differential settlement.

In landscape construction practice, embedding gabions in concrete is often chosen when there are heightened requirements for structural stability, when the structure is intended to be permanent and low-maintenance, or when adjacent infrastructure requires a dimensionally stable structure. It is not a one-size-fits-all solution, but rather a technically sound decision that influences planning, execution, and maintenance in equal measure.

Structure and Design Principle: Foundation, Basket, and Connections

The construction of a gabion structure set in concrete always begins with the foundation. Without a load-bearing foundation, any gabion wall—whether set in concrete or not—is at risk in the long term. For systems set in concrete, a reinforced concrete strip foundation is typically constructed, with dimensions determined by the wall height, soil class, and expected loads. As a general rule of thumb, the foundation width should be at least half the wall height, although precise dimensioning requires a structural analysis. The foundation depth must extend below the frost line, which in Germany ranges from eighty centimeters to one meter depending on the region.

Anchor rods or threaded rods are embedded in the still-fresh concrete foundation; these will later connect the gabion baskets to the foundation. These connecting elements are made of stainless steel or hot-dip galvanized steel and are positioned so that they can be threaded through the base plate of the gabion basket and secured with nuts. The baskets themselves consist of galvanized steel wire mesh, often with an additional plastic coating (PVC sheathing) for enhanced corrosion protection. The mesh size of the netting depends on the size of the stones used as fill material; common mesh sizes range from fifty to one hundred millimeters, with stone sizes selected to match.

Once the baskets have been placed on the cured foundation and secured with anchor rods, they are filled with fill material. For visible exterior surfaces, hand-selected natural stones are typically used and carefully placed in the outer layers, while the core area is filled with loose stones either mechanically or manually. In multi-layer constructions, the baskets in the upper layers are connected to those below using connecting wires or special clamps. If the entire structure is to be additionally secured with concrete, mortar can be applied to the joint area between the top edge of the foundation and the bottom of the basket, which, once hardened, creates a form-fit connection.

Concrete Grade and Binding Agents

Selecting the correct concrete grade is crucial for embedding gabions in concrete. For outdoor foundations exposed to freeze-thaw cycles, exposure class XF2 according to DIN EN 206 is recommended as a minimum; for exposure to de-icing salts, XF4 is recommended. Concrete of strength class C20/25 is sufficient for most gabion foundations, provided there are no exceptional load assumptions. For the connection between the basket bottom and the foundation, a trass cement mortar is also suitable, as it develops good adhesion to the concrete substrate while retaining a certain degree of flexibility.

Fastening elements between the baskets and to the foundation must be permanently corrosion-resistant, as they are inaccessible inside the structure and, in the event of damage, could only be replaced by dismantling the structure. Hot-dip galvanized steel in accordance with DIN EN ISO 1461 provides sufficient protection in most applications. In locations with aggressive environments, such as near road salt or in industrial settings, A4-grade stainless steel is preferable. These additional costs pay for themselves over the structure’s service life, which can span several decades if properly constructed.

Structural Principles and Drainage: What Designers Need to Know

Gabion walls, whether set in concrete or not, are gravity walls that derive their stability primarily from their own weight. Depending on the type of stone and the degree of filling, the weight of a filled gabion ranges between twelve thousand and twenty thousand kilograms per cubic meter, which is significantly more than that of concrete (approximately twenty-four thousand kilograms per cubic meter), but this is offset by the structure’s greater volume. For the structural analysis, resistance to sliding failure, overturning failure, and foundation failure must be verified. In structures set in concrete, anchoring in the foundation significantly improves resistance to overturning failure, which allows for taller retaining walls or steeper wall slopes than with unfounded systems.

Earth pressure considerations play a central role in gabion retaining walls. The active earth pressure acting on the rear wall surface depends on the slope angle, the unit weight of the soil, and the angle of internal friction of the surrounding soil. Due to their porosity, gabion walls can relieve water pressure, which is a significant advantage over solid concrete walls. This advantage is retained even in structures encased in concrete, as long as the baskets themselves are not filled with concrete and the fill material is sufficiently permeable. A drainage layer of gravel at the rear, connected to a drainage pipe, is a standard feature of any professionally designed gabion retaining wall.

An aspect that is often underestimated is the drainage of the foundation level. Standing water beneath the foundation can cause heaving during frost, which damages the connection between the gabion and the foundation. Therefore, the foundation should rest on a drainage layer at least twenty centimeters thick, consisting of crushed gravel or crushed stone, which is drained laterally or connected to a drainage system. This measure is particularly important for gabions encased in concrete, because the rigid connection no longer allows for settlement compensation, and even minor frost damage to the foundation can lead to cracks in the connection zone.

Applications in Open Spaces and Urban Planning

Concrete-encased gabions are used in a wide range of applications, ranging from small-scale garden design to large-scale infrastructure planning. In public open spaces, they are used as retaining walls on slopes, as edging for playing fields, as amphitheater-style seating structures, and as barriers around traffic areas. Their robustness and resistance to vandalism make them particularly suitable for heavily trafficked public spaces, where lighter structures would be quickly damaged.

In road and path construction, gabion walls set in concrete are used as slope stabilization on hillsides, as retaining walls alongside bike paths and sidewalks, and as noise barriers. The advantage over precast concrete elements lies in their aesthetic quality: the natural stone surface blends into the landscape, provides habitat for plants and animals in the gaps between the stones, and ages in an aesthetically pleasing way. At the same time, embedding the gabions in concrete makes the structure more durable and requires less maintenance than simply stacked systems, which can become unstable due to vibrations from traffic or construction work in the neighborhood.

In urban planning and urban open spaces, gabions are gaining importance as multifunctional elements. They can serve as a substructure for seating, as supports for greenery, or as a foundation for pergola structures. Gabions set in concrete provide the necessary structural stability to safely bear live loads. Projects that combine gabions with extensive greening utilize the voids in the stone material as a substrate for pioneer vegetation, thereby creating ecological benefits in densely built-up urban areas where every plantable surface counts.

Noise Barriers and Special Structures

When used as noise barriers, gabions are occasionally combined with special fill materials, such as recycled concrete, slag, or mineral waste materials, which offer a higher bulk density and thus better sound insulation values than lightweight natural stone. Concrete foundations are virtually mandatory for such structures because the wall heights and wind loads at exposed locations exceed the stability limits of unfounded systems. The sound absorption provided by the rough stone surface is an additional advantage over smooth concrete walls, which reflect sound rather than absorbing it.

Advantages and Limitations: An Objective Assessment

The advantages of embedding gabions in concrete are multifaceted. First, anchoring them in the foundation significantly increases structural stability and allows for wall heights that would not be structurally feasible without a foundation. Second, the form-fit connection prevents individual baskets from shifting or tipping due to uneven loads, vibrations, or frost action. Third, the structure is more durable because the connection points—which are often the weakest link in systems without a foundation—are protected by being encased in concrete. Fourth, the water permeability of the gabion wall is maintained even with a concrete foundation, provided the baskets are not filled with concrete, which preserves the advantage over solid retaining walls in terms of water pressure.

These advantages are offset by clear limitations. The most important is the loss of flexibility: gabions encased in concrete can no longer compensate for settlement of the subsoil. On non-homogeneous ground, such as backfill, peat soils, or on slopes with active creep movements, this rigidity can lead to cracks in the joint zone and ultimately to damage to the structure. In such cases, a thorough soil investigation prior to planning is essential. Another disadvantage is the limited reparability: While individual damaged baskets can be replaced in unfounded gabion systems, partial dismantling of structures encased in concrete involves considerable effort. Finally, deconstruction at the end of the structure’s service life is more labor-intensive and expensive than with flexible systems, which is a relevant consideration in the context of the circular economy and sustainable construction.

The decision for or against embedding in concrete should therefore always be based on a careful assessment of site-specific requirements. For low gabion walls up to about one meter in height on stable, even ground without traffic loads, embedding in concrete is often unnecessary and increases costs and effort without a proportional benefit. For wall heights exceeding one and a half meters, in the presence of traffic loads, or when there are special durability requirements, however, embedding in concrete is technically recommended.

Common Mistakes in Planning and Construction

The most common mistake when embedding gabions in concrete is a foundation that is too shallow or insufficiently reinforced. Failing to account for the frost line or choosing a foundation width that is too narrow risks frost damage and tipping failure as early as the first few winters. Equally problematic is the lack of drainage beneath the foundation: standing water and frost pressure can lift the foundation and damage the anchoring without this being immediately visible from the outside.

Another common mistake is the use of unsuitable fasteners. Plain structural steel without adequate corrosion protection will rust through within a few years when buried in the ground or in damp stone material. The result is a gradual loss of connection between the basket and the foundation, which only becomes apparent through tilting or cracking once the damage is already significant. Proper construction relies on materials with permanent corrosion protection, as described above.

Neglecting rear drainage is also a classic design flaw. Without a drainage layer behind the gabion wall, water pressure builds up during heavy rain or prolonged precipitation, jeopardizing the wall’s stability. Although gabions are water-permeable, if the underlying soil is poorly permeable, the baskets’ inherent drainage capacity is insufficient to relieve the water pressure quickly enough. A carefully planned drainage layer made of coarse-grained material connected to a drainage pipe is therefore not an optional detail, but a structural necessity.

Embedding Gabions in Concrete in the Context of Sustainable Open-Space Planning

Gabions have established themselves in open-space planning as a material with high ecological and design potential. The decision to encase them in concrete is not a departure from this potential, but rather a technical adaptation to specific requirements. However, anyone embedding gabions in concrete should consciously preserve the system’s ecological qualities: water permeability, the joint spaces as habitats, the use of natural materials, and the potential for vegetation. These qualities are lost when the baskets are completely filled with concrete, which in most cases is neither structurally necessary nor ecologically sound.

In the context of climate adaptation for urban open spaces, gabion walls encased in concrete offer interesting possibilities. Whether used as retention elements in retention basins, as edging for infiltration areas, or as a foundation for raised beds that utilize rainwater, they can combine water-sensitive open-space planning with durable construction. The porosity of the stone material supports evaporative cooling and helps regulate the microclimate, which is a significant contribution to heat resilience in densely built-up urban neighborhoods with a high degree of soil sealing.

Professionals planning to embed gabions in concrete should keep the structure’s entire lifespan in mind: from the site investigation through structural analysis and material selection to the question of how the structure can be dismantled or converted at the end of its service life. Gabions are not a “set-it-and-forget-it” solution that works without planning; rather, they are a construction system that only fully realizes its strengths when treated with the same professional rigor as any other civil engineering structure in the outdoor environment. Those who meet these standards will end up with a structure that lasts for decades, is environmentally sound, and is aesthetically pleasing.