Products intended for horizontal road marking are designed to be used especially on asphalt surfaces, which are a porous, rough substrate with a high proportion of bitumen.

The principle of adhesion of road coatings is based on the penetration and soaking of the bituminous binder and on the mechanical locking with the installation of asphalt base aggregates in the coating. They dry fast and feature suitable highly elastic properties, adapted to the specific characteristics of asphalt surfaces.

When planning the marking of high-wear concrete surfaces, where the surface is smooth, it is crucial to ensure good adhesion of coatings to such surfaces, as this will also ensure durability and a functional life span of the coating. Adhesion depends on the strength of the bond between the two materials in contact, which can be influenced by different mechanisms. These can be of a physical/chemical or mechanical nature. The basic characteristics of the surface, as well as of the type of coating, must be mutually compatible to guarantee a high-quality joint. The procedures in the final stages of concrete production are in fact those that will determine the key characteristics of the final surface, both in terms of surface composition and topology, and thus determine the possibilities of application and selection of the coatings used.

Pre-treatment of concrete surfaces

Concretes are critical substrates with different pore structures, and are often treated with a fine layer of mortar and means for further processing. In order to ensure compact adhesion, a suitable layer of extracted dry cement laitance must be removed from new concrete surfaces using appropriate methods (e.g. high-pressure water).

The porosity of concrete is one of the key risk factors for its durability, so various system solutions are used for its protection, which bring additional challenges for further colouring. For surface protection of concrete in road construction, we also use hydrophobic protective agents based on silanes, siloxanes and silicones. We must also pay special attention to concrete surfaces that have been additionally treated with water glass. The latter can be found 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 is closed, which prevents the penetration of the coating and its mechanical anchoring to the surface. Surfaces that have been treated in this way are usually problematic for the adhesion of most coatings and require mandatory preliminary testing.

Role in concrete and the occurrence of bubbling

Moisture in the concrete should not exceed 4% (measured by the CM method, up to about 20 mm of measurement depth) in order to achieve adequate adhesion of the marking materials to concrete surfaces. The requirement applies to all types of materials, including primers used for surface preparation. An exception to this rule is the Signocryl 2K epoxy coating, which dries and cures even in humid conditions.

Evaporation of water on the surface of concrete causes the following:

• Water that accumulates on the concrete surface and under the coating weakens the contact between the material and the surface. Freezing and even minor mechanical strain can cause the markings to peel off.
• Interferences in the curing of cold and cold spray plastics due to the changes in the physical properties of materials.
• Possibility of an alkaline chemical reaction as a result of the capillary water weakening the binder and marking characteristics.
• Formation of bubbled due to the osmotic pressure.
• When isocyanate hardeners are used, CO² is formed through the reaction with moisture, which leads to the formation of bubbles and weakens the crosslinking of the film.

In principle, the concrete must be left for at least 28 days for all the components to bind and for the concrete to dry.

Surfaces in parking garages and industrial premises

Heavy work machinery load, temperature fluctuations and spills of various chemicals are daily occurrences in such premises. When considering mechanical loads, the expected load, dynamic factors due to traffic in the premises, resistance to wear and abrasion and, last but not least, resistance to impacts and falls of heavy objects are the important ones. We also need to know if the surface will be exposed to direct sunlight and consequently UV rays. There are no rules on how marking should be made in garages and industrial halls, or which materials should be used. Standards are not used for this kind of work, which is why a clear agreement between the investor and the contractor on the expected execution of work and the expected quality or purpose of the marking is previously required.

Surface preparation

Before application, surfaces intended for marking must be dry, clean, free of dust, oils and grease and without free abrasive sand or other impurities. Contamination poses a high risk in ensuring high-quality adhesion of materials to the surface and is often the cause of problems in establishing responsibility for a poor completion of work.

Adhesion test

The following possible test methods can be used to check adhesion:

• manual adhesion test without determination of values,
• adhesion test by tearing off seals in accordance with EN ISO 4624,
• cross-cut test in accordance with DIN 53151.

The test field where the adhesion of the coating is checked usually consists of a part that is pre-treated beforehand (surface preparation, sanding, cleaning) and a parallel untreated surface. One week for proper curing of the coating is usually required in order to test the adhesion. Tests are performed on both surfaces with a size of 1-2 m², and at least five places for measurements are determined.

Suggested solutions

According to the described situations, expectations and requirements, Helios has prepared three system sets that ensure a suitable implementation of horizontal marking on different concrete surfaces.

1. Standard concrete surfaces without special treatment:

a. use of SIGNO primer 2K PUR, which ensures adequate adhesion of the selected coating;

b. depending on the needs, we can choose standard paints, such as Signocryl, or cold type plastics, such as Signodur.

2. Concrete surfaces which are additionally cured and smoothed with quartz sand – the surfaces are not chemically treated:

a. a primer is only needed when curing old concrete surfaces;

b. it is best to use Signocryl 2K PUR, Signocryl Traffic 2K PUR, and Signocryl 2K epoxy.

3. Various industrial floor coatings (epoxy, PU ...) and additionally chemically treated concrete surfaces:

a. Signo primer 2K PUR and the Signocryl 2K PUR coating (mandatory test field with an adhesion test);

b. Two coats of Rezistol enamel 2K PUR; c. first coat of Rezistol E DBS to ensure adhesion, and Rezistol enamel 2K PUR for faster curing.

Warning

We suggest performing test fields and checking the adhesion of the coating to the surface for each item.