The mortar layer is seemingly narrow yet in practice a structurally important component in construction. It bonds components, compensates tolerances, distributes loads, and influences the behavior of masonry and concrete elements in operation as well as during deconstruction. For concrete demolition and special demolition, interior demolition and concrete separation/cutting as well as in rock excavation and tunnel construction or natural stone extraction, the mortar joint often acts as a natural separation or weakness zone. This has immediate effects on the selection and guidance of tools such as concrete demolition shears or rock wedge splitters and concrete splitters from the Darda GmbH portfolio.
Definition: What is a mortar layer
A mortar layer is the intermediate or bedding layer of mineral mortar between components. Typical applications are bed and head joints in masonry, adhesive layers in thin-bed construction, grouting and undergrouting zones on a machine foundation, leveling layers under screeds, and bonding and leveling layers under plaster. Mortar essentially consists of binder (e.g., cement or lime), aggregate, and water; admixtures and additives control properties such as workability, strength, adhesion, and durability. Depending on the method, thickness ranges from thin-bed (approx. 1–3 mm) to classic bed joints (approx. 10–12 mm) and beyond for grouting tasks.
Properties and key parameters of the mortar layer
For planning, repair, and deconstruction, key parameters such as compressive and flexural tensile strength, shear strength in the joint, pull-off strength to the adjacent material, modulus of elasticity, porosity, water absorption, and state of carbonation are decisive. High-strength, dense mortars transfer loads efficiently and produce a hard, more brittle joint; softer or aged mortars often show lower shear and bond strengths, which can be used deliberately in selective deconstruction. Applicable standards and test methods can vary depending on use case (e.g., masonry mortar, repair mortar, or grouting mortar); they should be checked on a project basis and, if in doubt, validated by appropriate investigations.
Structure, composition, and typical thicknesses
Depending on the use, the composition of the mortar layer differs: cement or lime mortars in masonry, thin-bed mortars with fine aggregate, hydraulically setting grouting mortars under machine plates, or polymer-modified systems in refurbishment applications. Typical thicknesses are:
- Thin-bed mortar: approx. 1–3 mm
- Conventional bed joints: approx. 10–12 mm
- Leveling and grouting mortars: often 10–50 mm (project-specific)
The actual mortar bed thickness influences load distribution behavior, joint stiffness, and the subsequent guidance of separation joints in demolition and cutting work.
Role of the mortar layer in load-bearing behavior and deconstruction
In masonry, the mortar layer as a bond zone governs load transfer between units. In composite elements (e.g., overlays or masonry-to-concrete connections), it controls adhesion between layers. For deconstruction, it is crucial whether the mortar layer dominates the bond or is already weakened:
- Weakened or carbonated mortar layers facilitate controlled release of bonded components.
- High-strength, dense mortars often require targeted pre-separation, e.g., by splitting or shear demolition with high edge precision.
Tools such as concrete demolition shears can grip masonry bonds along the joints and break them in a controlled manner. Rock wedge splitters and concrete splitters use the joint as a weakness zone and produce low-stress separations in masonry or in transition areas to concrete. Hydraulic power packs supply these tools efficiently and enable reproducible process parameters in concrete demolition and special demolition.
Distinction by function: joint, adhesive layer, grouting, injection
Bed and head joints
They serve to transfer loads and to compensate unevenness. Their properties (thickness, strength, moisture content) largely determine how a component behaves during separation, splitting, or shear demolition.
Adhesive layers (thin-bed)
Thin-bed mortar creates a stiff bond at small thickness. During deconstruction, the bond is often so high that concrete demolition shears with defined jaw openings or precise split points are advisable to initiate cracks in a targeted manner.
Grouting and undergrouting mortars
Under machine plates and foundations they create full-surface contact. When releasing such plates, the grouting zone can be pre-split by rock wedge splitters and concrete splitters to minimize vibrations and avoid settlements in adjacent areas.
Injection and filling mortars
They increase the bond in cracks or joints. During interior demolition and concrete separation/cutting, the increased bond effect should be considered to avoid unexpected load redistribution.
Investigation and assessment of the mortar layer in existing structures
A systematic investigation reduces risks during deconstruction and improves the planning of cutting and splitting processes:
- Visual inspection of joint pattern, cracks, efflorescence, and hollow areas
- Simple field tests (knife test, scratch hardness) to estimate strength
- Sampling small drill dust to indicate moisture and binder
- Pull-off or shear tests at representative locations (if feasible)
- Assessment of moisture, freeze–thaw de-icing salt effects, and carbonation depth
The results guide the choice of separation lines and the tuning of tools. A brittle-hard joint often requires higher initial energy when initiating separation cracks; softer joints provide entry points for concrete demolition shears with controlled fracture guidance.
Influence of the mortar layer on equipment selection
The joint condition is a central parameter for selecting the approach in concrete demolition and special demolition as well as in interior demolition:
- Concrete demolition shears: For masonry walls and composite zones when joints are to be used as guide lines. Suitable for separating components step by step with low vibration.
- Rock wedge splitters and concrete splitters (incl. rock wedge splitter): For massive elements, foundation bearings, or natural stone bonds where the mortar layer serves as a weakness and splitting wedges define the separation joint.
- Multi Cutters and hydraulic shear: When reinforcement, inserts, or mixed composites also need to be cut.
- Steel shear: For cutting exposed rebar after breaking up the mortar layer or for selective deconstruction of steel components.
- Hydraulic power packs: For constant, finely metered power to the attachments, especially for sequential splitting and shear operations.
Work preparation: separation/cutting, splitting, and shear demolition depending on the joint
A structured procedure increases the safety and quality of separations:
- Analyze the existing structure: record joint type, thickness, strength, moisture, and bonding partners.
- Define separation lines: use the joint course as a natural line, observe edge distance.
- Coordinate equipment selection: concrete demolition shears for controlled fracture guidance, rock wedge splitters and concrete splitters for low-stress pre-separations.
- Plan the sequence: pre-separate/split, expose reinforcement, separate metal with steel shear.
- Low-emission execution: minimize dust, noise, and vibrations; consider dust extraction and shoring.
- Continuous control: check fracture progress, adjust parameters at the hydraulic power pack as required.
- Safe removal: consider unit weights, load paths, and support conditions.
Such standardized procedures support reproducible quality in special demolition and reduce the risk of consequential damage to adjacent components.
Challenges with historic and high-strength mortars
Historic masonry with lime-bound mortars often shows different fracture behavior than cement-bound systems. Softer, porous joints may break out unevenly; here a careful, step-by-step approach with concrete demolition shears helps. For high-strength thin-bed or grouting mortars, by contrast, introducing targeted split points with rock wedge splitters and concrete splitters is useful to activate the joint in a controlled manner. In rock excavation and tunnel construction as well as in natural stone extraction, mortar joints resemble geological weakness zones: splitting cylinders can act effectively there without excessively loading surrounding structures.
Damage patterns, repair, and deconstruction concepts
Cracking, efflorescence, voids, spalling, or frost damage in the mortar layer change load-bearing and separation behavior. In refurbishment, renewing or strengthening the joints (e.g., repointing, undergrouting) influences future disassemblability. Deconstruction concepts should consider this in advance: a strengthened bond may require additional separation steps; a weakened bond, on the other hand, allows larger cycles with concrete demolition shears and reduces the need for pre-cuts.
Material separation and documentation in special demolition
The mortar layer determines how cleanly materials can be separated. Clean separation joints make it easier to separate brick, natural stone, concrete, and mortar residues. Structured documentation of joint qualities, equipment parameters, and demolition steps supports quality assurance and the future reuse of materials. Requirements for disposal and recycling must be checked on a project-specific basis and should always be implemented in compliance with the applicable regulations and framework conditions.