Primers, as a preparatory layer, create a reliable bond between the substrate and the subsequent system—whether repair mortar, surface treatment, corrosion protection, or shotcrete. In the environment of Darda GmbH, where concrete, steel, and natural stone are processed, separated, or selectively removed with concrete demolition shears, hydraulic rock and concrete splitters, or other hydraulic tools, the correct primer determines the adhesion, durability, and functional reliability of the subsequent work steps.
Definition: What is a primer
Primer refers to a preliminary coat or preparatory treatment of the substrate that consolidates its surface, regulates absorbency, improves adhesion, and, depending on the product, also provides corrosion protection or acts as a barrier. In practice, this includes reactive resin primers (e.g., epoxy, polyurethane), mineral bond coats and pore densifiers (e.g., silicate systems), aqueous dispersions for dust binding, and zinc-rich primers for steel surfaces. The objective is a defined, reproducible interface zone between substrate and subsequent system that withstands mechanical, chemical, and climatic influences.
Use and significance in concrete demolition and specialized deconstruction
When removing material with concrete demolition shears, rough fracture edges, exposed reinforcement, and locally compacted edge zones are created. Controlled splitting with rock and concrete splitters produces sharp joints and fracture faces. These substrates require targeted priming to ensure the reliability of subsequent tasks such as reprofiling, crack injection, waterproofing, or establishing a bond. This is particularly relevant in concrete demolition and deconstruction workflows.
Follow-on tasks after removal
Typical follow-on tasks include tying in repair mortars, applying surface treatment systems, leveling prior to coatings, or preparing adhesive bonds. A suitable primer reduces dust, binds loose particles, regulates absorbency, and provides the necessary bond coat. On highly absorbent or porous concrete surfaces, capillary-active or reactive primers have proven effective; for damp substrates, moisture-tolerant systems must be selected.
Corrosion protection for exposed reinforcement
If reinforcing bars are exposed during shear work, temporary or permanent corrosion protection is required. Cementitious passivating coatings or reactive corrosion protection primers are applied to derusted, sound steel. The primer must be compatible with the planned mortar or coating system and must not impair adhesion at the concrete edge.
Substrate analysis and preparation
Any priming follows the rule: only as good as the substrate. Before selection and application, the condition and properties of the surface must be determined—especially after mechanical removal with demolition shears or after splitting operations.
Checks on concrete
- Strength and cohesion of the surface zone (pull-off strength, scratch test)
- Cleanliness: free of dust, laitance, release agents, oils, bitumen, coating residues
- Moisture content and moisture transport (capillary, residual moisture, standing water)
- Surface texture and roughness (fracture faces, edge breakouts, voids)
- Chloride contamination and carbonation in the area of exposed reinforcement
Preparatory measures
- Mechanical cleaning and dust removal (vacuuming, brushing, blasting where appropriate)
- Removal of unsound areas, breakup of sintered layers
- Establish a uniform surface texture to achieve defined consumption
- Mask adjacent components; protect against moisture and soiling
On steel surfaces that become visible after separation work on reinforced-concrete elements, suitable mechanical surface preparation is followed by immediate priming to prevent flash rust.
System types and selection criteria
The choice of primer depends on the substrate, environmental conditions, and the subsequent system. Frequently used types are:
- Epoxy resin primers: high pull-off values, good pore consolidation, partly barrier-forming; sensitive to residual moisture.
- Polyurethane/hybrid primers: broader moisture tolerance, more elastic, suitable for temperature fluctuations.
- Mineral bond coats: cementitious systems for bonded mortars and reprofiling, often applied fresh-on-fresh.
- Silicate/silane primers: hydrophobizing, pore-consolidating, to reduce water uptake and dusting.
- Zinc-rich steel primers: cathodic corrosion protection for exposed reinforcement and steel parts.
Selection criteria in practice
- Substrate material (concrete, masonry, natural stone, steel) and condition
- Moisture and temperature at the component, dew point margin, climate control
- Compatibility with repair mortars, coatings, or shotcrete
- Mechanical and chemical loads on the later system
- Application window, open time, and recoat intervals
- Emission requirements and occupational safety (e.g., reduced VOCs)
Application: steps and common mistakes
A careful, straightforward sequence minimizes risks and ensures reproducible results.
Procedure
- Prepare, clean, de-dust, and inspect the substrate.
- Mix the product (homogenize components, observe induction time).
- Carry out a test application on a small area; assess consumption and penetration depth.
- Apply evenly by roller, brush, or suitable spray method; avoid puddling.
- On absorbent substrates, if necessary, apply a second thin layer “wet-on-wet”; the goal is a saturated but not glossy, standing surface.
- Observe waiting times and recoat windows; verify pull-off adhesion values by spot checks.
Common sources of error
- Application on substrates that are too damp or too cold (poor film formation, blistering)
- Over-application and puddling (barrier effect, reduced adhesion)
- Insufficient cleaning after shearing or splitting operations (dust film reduces adhesion)
- Incompatible systems (e.g., solvent-based primer under a water-based mortar)
- Failure to observe recoat times (interface embrittlement)
Priming in rock excavation and tunnel construction
During heading and securing works, primers and bond coats serve as the interface between rock/natural stone and shotcrete or injection systems. On dusty, heterogeneous rock surfaces, dust-binding and pore-consolidating primers minimize the risk of debonding. In damp or water-bearing zones, mineral, moisture-tolerant systems or specific bond coats are advisable to establish a durable connection.
Specifics on natural rock surfaces
Varying mineralogy, joints, and differing absorbency require trial areas. Primers should not unnecessarily restrict vapor diffusion and should remain color-neutral if exposed finishes are planned.
Natural stone extraction and processing
During the extraction and processing of natural stone by splitting techniques, fracture surfaces are created that are later prepared for bonding, consolidation, or protective treatments. Low-viscosity mineral or silane primers penetrate capillary zones, reduce powdering, and improve the adhesion of adhesive mortars or protective layers without altering the appearance.
Strip-out and cutting: steel and composite components
In strip-out, beams, plates, and reinforcement are exposed or separated, for example with steel shears or cutting torches for tanks. After cutting, immediately priming the cut edges is essential to limit corrosion and to prepare subsequent work (e.g., coating, fire protection build-up). Surface preparation depends on the degree of contamination and the required cleanliness level; the primer is applied as soon as possible after surface treatment.
Coordination with rock and concrete splitters and concrete demolition shears
The joints produced by rock and concrete splitters offer a defined, often relatively clean fracture face. Depending on porosity, a low-viscosity primer may be required to penetrate sufficiently. Concrete demolition shears can create locally compacted edge zones; here, light blasting or brushing prior to priming is recommended so that the primer reaches sound microstructure. In both cases, the primer should be chosen to take advantage of the natural roughness without completely sealing capillaries if a mineral bonded system is to follow.
Environmental and occupational safety
During application, protective measures against dust as well as solvent and irritant exposure must be taken. Personal protective equipment, adequate ventilation, and proper disposal of residual quantities are essential. Requirements from technical data sheets and generally accepted rules of the trade must be observed; project-specific requirements may go beyond these.
Quality assurance and documentation
Simple, practice-oriented tests support execution: determining substrate moisture, measuring wet or dry film thickness, pull-off adhesion tests on sample areas, and photo documentation of pre- and post-treatment. Aligning product recommendations with the planned mortar or coating systems prevents incompatibilities. For critical components, trial areas and approvals are advisable.
Demarcation: When is a primer not required?
In some systems, a mineral bond coat applied fresh-on-fresh is used instead of a separate primer. On very dense, dry, and dust-free concrete surfaces, direct application can be permissible if the subsequent system provides for it. Likewise, highly modified repair mortars may require defined pre-treatments without a separate primer. Decisive factors are system compatibility and evidence of sufficient pull-off adhesion values under the expected boundary conditions.