Mortar is a mineral construction material that bonds components, compensates for unevenness, closes joints, and protects surfaces. It forms the link between masonry units, natural stone blocks, or components made of concrete. In deconstruction, building gutting, and cutting operations, the mortar layer often acts as the weakest zone or as a deliberately usable separation joint. This property significantly influences the selection and operating method of tools such as concrete demolition shears, stone and concrete splitters, or stone splitting cylinders from Darda GmbH in fields such as concrete demolition and deconstruction, rock excavation and tunnel construction, as well as natural stone extraction.
Definition: What is meant by mortar
Mortar is a mixture of a binder (e.g., cement, lime, or blended binders), fine aggregates (sands, powders), water, and, if necessary, admixtures or additives. It is used for masonry laying, jointing, plastering, grouting, and repair. In contrast to concrete, mortar contains no coarse aggregate (gravel, chippings). Hardening occurs depending on the binder through hydration (cement), carbonation (lime), or a combination of both processes. Depending on the formulation, workability, bond tensile strength, compressive strength, water uptake, and durability are specifically adjusted.
Fundamentals: Composition and properties of mortar
The performance of a mortar arises from the interaction of binder, particle size distribution, water content, and admixtures. Decisive factors are the consistency during application, adhesion to stone or concrete, shrinkage and deformation behavior, and resistance to freeze–thaw with de-icing salts, moisture, chemical attack, and abrasion. A low water–binder ratio typically increases density and strength but can limit workability. Well-graded fine sands improve packing density and reduce pores. Lime content increases plasticity and wetting of the joint flanks, while cement provides early strength development and high final strengths.
Types of mortar and typical applications
Mortar is tailored to requirements—from masonry mortar in solid construction to grout or repair mortar in existing structures. The selection influences not only new-build processes but also deconstruction strategies and tool-conserving separation techniques.
- Masonry mortar (e.g., lime mortar, cement mortar, lime-cement mortar): for exterior and interior masonry; key parameters are compressive strength, deformability, and bond tensile strength.
- Thin-bed mortar: very fine, for planar masonry units; thin joint thicknesses, targeted brittleness—relevant in selective deconstruction.
- Plaster mortar: as protective and leveling layer; influences dust and fracture behavior during removal.
- Joint mortar: for closing and shaping joints; abrasion resistance and water uptake are decisive.
- Grout and anchor/injection mortars: from flowable to expansive, for undergrouting, machine foundations, anchors, and cavity filling.
- Repair mortars: matched to the existing fabric, from low-reactive lime mortars to polymer-modified systems.
- Expansive mortar (non-explosive): generates stresses through volumetric expansion to drive cracking and fracture in rock or concrete; as a chemical demolition method alternative or complement to mechanical methods.
Mortar in concrete demolition and special demolition
In deconstruction, mortar is often used as a planned sequence of weak zones. Joints can be opened, connections separated, and composite action between components deliberately released. Concrete demolition shears engage at edges, joints, and layer interfaces to initiate crack formation in a controlled manner. Hydraulic rock and concrete splitters use boreholes and existing mortar or transition zones to promote brittle fracture. This minimizes vibrations, noise, and secondary damage, while material fractions (concrete, stone, mortar) can be collected more cleanly separated by type.
Selective deconstruction: Open joints instead of destroying components
Where masonry, natural stone bearing surfaces, or composite joints are present, it pays to focus demolition forces on mortar zones. Lower density and brittleness of mortar often lead to more defined fracture lines compared to the stone or concrete matrix. Concrete demolition shears can be applied with moderate forces to shear or crush joints before addressing load-bearing areas. This reduces crushing forces, dust, and rework.
Expansive mortar as an alternative or complement
Expansive mortar builds pressure with a time delay and can pre-relieve or separate components. In massive, hard-to-access areas, it can be combined with mechanical methods: first inducing cracking with expansive mortar, then controlled opening with concrete demolition shears or subsequent splitting with stone and concrete splitters. Processing conditions (temperature, drilling pattern, curing time) are decisive. Chemical procedures always require careful work and compliance with product-specific instructions and disposal routes.
Relevance of the mortar structure for concrete demolition shears and stone and concrete splitters
For the working strategy, the structure is crucial: binder type, joint width, moisture level, and state of aging govern the crack pattern. Cement-rich, dense mortars transmit higher shear forces; lime-rich, more porous mortars favor more brittle separations. Concrete demolition shears exploit these differences at joint flanks, recesses, or plaster runouts. Stone and concrete splitters as well as stone splitting cylinders work efficiently when drilling pattern and wedge direction are aligned with joints and stratification; hydraulic power packs (power units) provide uniform pressure build-up for reproducible splitting results.
Drilling pattern and mortar structure
Boreholes are ideally placed to create stress concentrations along joints or transitions. Closer spacing and alignment parallel to mortar layers promote crack propagation. In heterogeneous masonry, a variable drilling pattern is advisable to bypass hard inclusions or reinforcement. Damp mortar damps crack propagation; dry joints break more brittly—this affects the force required and the sequence of attack points.
Natural stone extraction, rock excavation, and tunnel construction: Mortar as auxiliary and stabilizing material
In geotechnical applications, mortars are used as grouts or anchor fillers to close voids, transfer loads, or consolidate surfaces. When releasing blocks in natural stone extraction, natural bedding planes and existing separation joints favor the use of stone and concrete splitters; mortar can serve as a temporary support or grouting material. In tunnel construction, grouted mortars stabilize contact zones before controlled splitting or cutting work takes place.
Building gutting and cutting: Assess mortar in existing structures deliberately
Existing buildings often present heterogeneous mortars: historic air lime mortars, trass-bearing mixes, cement-rich joints, or modernized repair spots. For building gutting and cutting, knowing this variety is essential. Soft mortars can be sheared and raked out; hard joints demand higher point loads and precise starter cuts. Concrete demolition shears can initiate breaks on component edges with plaster-and-joint packages before separating load-bearing layers; with a dense joint matrix, pre-drilling and splitting is advisable.
Production, handling, and quality assurance of mortar
The mixing sequence (first homogenize dry constituents, then add water and any admixtures), mixing time, and temperature determine consistency. Too much mixing water increases porosity and reduces strength; re-tempering already stiffening mortar is to be avoided. Uniform curing (keeping moist, protecting from drafts and solar radiation) reduces shrinkage and cracking. For quality assurance, simple spot checks (consistency, density) and—if required—test specimens for compressive or pull-off testing are used.
Environmental and health protection
Cement-containing mortars are alkaline and can irritate skin and eyes. Dust exposure must be limited; appropriate personal protective equipment, low-dust processing, and proper disposal of mineral residues must be planned. During deconstruction, emissions (dust, noise, vibrations) are to be minimized and adjacent components protected.
Typical damage patterns and repair
Cracks due to shrinkage, salt loading, freeze–thaw/de-icing attack, or improper mortar formulations are common failure causes. Repair mortars must match the existing structure in stiffness, strength, and water balance. Repairs that are too stiff on soft substrates lead to edge spalling; mortars that are too porous increase water uptake. Before interventions, sampling and testing are advisable to assess bond and compatibility—especially if concrete demolition shears or splitters will subsequently work at cut edges.
Standards and classification
For masonry mortars and plaster mortars, European standards specify requirements for compressive strength classes, bond strength, water uptake, and frost resistance (e.g., classifications such as M2.5, M5, M10). For grout and repair mortars, additional requirements for flow behavior, shrinkage, and early strengths apply. Standard-compliant selection and documented processing facilitate later deconstruction, construction waste sorting, and planning of tool-appropriate separation methods.
Practical guide: Selection, use, and demolition strategy
- Survey the existing structure: masonry type, joint widths, mortar type (visually, by feel, and by sampling if needed).
- Define the goal: separating, releasing, notching out, opening—depending on the component and follow-up work.
- Set the strategy: use joints as separation lines, pre-drill hard composites, shear soft joints.
- Tool selection: concrete demolition shears for controlled crushing and shearing at joints; stone and concrete splitters for linear separations along drilling patterns; stone splitting cylinders in thick sections; hydraulic power packs for uniform pressure build-up; supplement with expansive mortar as needed.
- Plan the drilling pattern: align direction and spacing with mortar layers, stratification, and reinforcement layout.
- Execution: increase stress progressively, monitor crack propagation, vary attack points.
- Finishing: selectively remove joint residues, secure fracture surfaces, separate materials cleanly by type.