Products intended for horizontal road signalization are primarily designed for use on asphalt surfaces, which exhibit porous and rough structure with high content of bitumen in their composition. The principle of adhesion for road coating is based on surface penetration and partial dissolution of bituminous binder, followed by mechanical incorporation of asphalt base aggregates in the coating. Road marking coatings are characterized by fast drying/curing and suitable viscoelastic properties, adapted for the thermal expansion and contraction of asphalt surfaces. When planning the marking of loaded concrete surfaces, it is crucial to ensure good adhesion of coatings to such surfaces, as this will also determine the durability and functional life of the coating. The adhesion depends on the strength of the bond between the two materials in contact, where the contribution of different mechanisms may be involved. These can be of a physio-chemical or mechanical nature. The basic characteristics of the substrate as well as the type of coating must be mutually compatible for a quality joint. It is the procedures in the final stages of concrete finishing that will determine the key characteristics of the surface, both in terms of composition and topology of the surface, and thus determine the possibilities of application and selection of the applied coatings.
Pre-treatment of concrete substrates
Concrete substrates can exhibit different structure of surface porosity due to different finishing techniques and are often treated with a fine layer of mortar and after-treatment agents. On new concrete surfaces, it is mandatory to remove the layer of extracted dry cement milk by appropriate methods (ex. high-pressure water) to ensure a compact adhesion. The porosity of concrete is one of the key risk factors for its durability, so its protection uses various system solutions, which, however, bring additional challenges for further coloring. Hydrophobic agents based on silanes, siloxanes and silicones are used for surface protection of concrete in road construction. Special attention should also be paid to concrete surfaces that have been additionally treated with water glass, which appears on the market under a wide range of commercial names and is used as a surface protection of porous concrete against the penetration of water, oils, and other liquids. In all cases, the open porosity closes, which prevents the penetration of the coating and its mechanical anchoring to the surface. Surfaces treated in this way are usually problematic for the adhesion of most coatings and require mandatory preliminary pull-off testing.
Formation of defects and poor durability of markings due to moisture content in concrete
The moisture in the concrete should not exceed 4% (measured by the CM method, up to about 20 mm of measuring depth) for achieving adequate adhesion of the marking materials to the concrete substrates. The requirement applies to all types of materials, including primers intended for surface preparation. The exception is Signocryl 2C Epoxy coating, which dries and cures even in humid conditions.
Possible causes and effects due to moisture evaporation from concrete surface:
- Accumulated water at the interface of concrete surface and coating weakens the contact and inter-bonding between material and the substrate. Freezing and even minor mechanical stress can cause the markings to peel off.
- Disturbances in the curing of cold plastics, due to changes in the physical properties of materials.
- Possibility of alkaline chemical reaction due to capillary water, affecting physio-chemical characteristics of binder and durability of marking.
- Bubble formation due to osmotic pressure.
- At polyurethane coatings, cured of isocyanates, reaction with moisture proceeds preferentially, which leads to formation of bubbles and decreases the crosslinking and final hardness of the film.
Thus, there is high importance of leaving the concrete to settle down properly over a period of at least 28 days, to completely cure and dry for further marking purposes.
Substrates in parking garages and industrial premises
Loads of heavy work machinery, temperature fluctuations and spills of various chemicals are a daily occurrence in such premises. In respect of mechanical loads, it is highly important to evaluate the expected daily load and dynamic factors caused by traffic, imposing requirements regarding resistance to wear, to impacts due to falls of heavy objects and abrasions of (fork-lift) trucks. Furthermore, exposure to UV needs to be defined beforehand for selecting type of coating with suitable UV stability properties.
The implementation of markings in garages and industrial halls is not determined by any rules, as well as the choice of materials. The road marking standards are not used/applied in this segment, so a clear agreement between the investor and the contractor on the expected execution of works and the expected quality or purpose of surface markings is previously required.
Surfaces intended for marking must be dry, clean, free of dust, oils and greases and free of abrasive sands and other impurities before application. Contamination poses a high risk in ensuring quality adhesion of materials to the substrate and is often the cause of problems in finding responsibility for poor quality work.
Pull-off adhesion testing of coatings
The following possible test methods may be selected to evaluate quality of adhesion:
- Manual grip test (qualitatively without quantifications)
- Adhesion pull-off test on a single coating or a multi-coat system with the use of dolly in accordance with EN ISO 4624
- Cross-cut test in accordance with DIN 53151
The test field for preliminary evaluation of adhesion quality usually consists of an untreated surface segment, which is tested in parallel to pre-treated substrate (surface preparation; sanding, cleaning, etc.). Adhesion tests are performed on both surfaces in the range of 1-2 m2,
and at least 5 locations are selected for measurements. One week shall be provided for adequate hardening of applied coating before executing test.
Proposed coating solutions
According to the described situations, expectations and requirements, Helios offers three system assemblies that ensure the appropriate implementation of horizontal signalization on different concrete surfaces.
a) Standard concrete surfaces, without special treatment:
- Use of SIGNO Primer 2C PUR, which ensures adequate adhesion of the subsequent selected coating
- Depending on the needs, we can choose standard colors of the SIGNOCRYL type or cold plastics of the SIGNODUR type.
b) Concrete surfaces additionally hardened and smoothed with quartz sand – surfaces not chemically treated:
- Primer coat is only needed if the case of older concrete surface, requiring pretreatment
- Suitable selection of coating paints are SIGNOCRYL 2C PUR, SIGNOCRYL Traffic 2C PUR or SIGNOCRYL 2C Epoxy.
c) Various industrial flooring (epoxy/PU) or additionally chemically treated concrete surfaces:
- SIGNO primer 2C PUR and SIGNOCRYL 2C PUR coating (mandatory test field with adhesion check)
- RESISTOL enamel 2C PUR two layers
- REZISTOL E DBS first layer to ensure adhesion and REZISTOL enamel 2C PUR for accelerated hardening of finishing layer
NOTE: To assure compatibility and suitability of each system assemblies with target concrete flooring to be coated, we suggest performing test fields and checking the adhesion of the coating to the substrate beforehand.