Often, when buying paints and varnishes or plaster compositions, one hears the phrase: “the product provides good adhesion” or “excellent adhesive properties”. The meaning of the term is often unclear. Let's find out what adhesion is, why is it necessary and why is it so important?
Determination of adhesion
Thanks to this phenomenon, paint and plaster are firmly held on the walls and ceiling, concreting is possible. As it becomes clear, it is responsible for bonding the surface or substrate to the coating.
Adhesion is the adhesion of dissimilar substances. In construction, this term refers to the ability of a particular coating (for example, paintwork, plaster) to firmly adhere to the base surface.
Adhesion is divided into physical and chemical:
- In the first case, the bond arises due to the adhesion of the molecules of the materials.
- In the second - due to the chemical effects of substances.
Bonding intensity is measured in MPa (megapascals). This figure indicates the force that will have to be applied to separate the coating from the base. For example, if the label says that the agent provides adhesion of 1 MPa, then in order to tear it off, you will have to apply a force of 1 N for each mm2 (about 100 g / mm2).
Adhesion properties are one of the main characteristics for any coating, decorative or protective. The strength and reliability of the connection, the possibility of gluing certain types of materials, the comfort or laboriousness during the work depend on them.
For which materials is adhesion important?
This indicator is of primary importance for building and finishing compositions. Be sure to pay attention to the level of adhesion for the following types of coatings:
- Lacquers and paints. This property affects the quality of adhesion, the depth of penetration and the durability of the coating. The higher the indicators, the better and longer the paintwork materials on the base will hold.
- Gypsum mixtures. The quality of adhesion determines the possibilities of decorative finishing.
- Cement-sand compositions. The safety of the building often depends on the reliability of gluing. For example, when using substances with poor adhesion, brickwork will not last long.
- Sealants and other adhesives. Here you need to know between which materials the agent is able to provide adhesion. When using unsuitable mixtures, the quality of the connection deteriorates, and in some cases it becomes completely impossible.
To measure the adhesive ability of materials and to control the quality of adhesion of the coating to the base allows a special device - an adhesive meter.
Adhesion enhancement methods
The adhesive properties of materials can be both improved and worsened. This is a non-constant value. For example, various impurities are added to the compositions applied to the surface, which increase the ability to penetrate and adhere. Substances that play the role of an intermediate layer are used, for example special primers or contact fluids.
Degreasing the surface is another sure way to enhance the bonding ability.
To increase adhesion, a whole range of measures is used to influence the physical and chemical properties of the material. There are 3 surface preparation methods that improve adhesion:
- Mechanical. This can be abrasive treatment for roughening, notching, as well as cleaning from dust and any contaminants.
- Chemical. Mixing special additives and plasticizers into the applied solution.
- Physical and chemical. It includes processing with primers, as well as puttying.
Such methods are most effective when bonding dissimilar surfaces with different physical and chemical properties.
In addition, there are a number of factors that reduce the quality of adhesion of materials:
- It is almost impossible to glue dusty or greasy surfaces without pre-treatment with cleaning and degreasing compounds.
- The quality of adhesion will be very low even if one or both surfaces are treated with a composition that reduces porosity.
- Adhesive properties may deteriorate during setting and drying of materials. During the transition from a liquid to a solid state, the chemical and physical properties of substances can change. For example, many solutions shrink. As a result, the area of contact with the base is reduced. Then tensile stresses appear, due to which, in turn, cracks form. As a result, the adhesion of materials becomes less durable, unreliable.
A simple example. If you plaster a concrete wall without proper preparation, the coating will quickly fall off. This is due to many factors, which include:
- surface dusting;
- shrinkage of the plaster layer;
- no additives that enhance adhesion, etc.
Therefore, when working with old concrete, an integrated approach should be used, for which you need:
- thoroughly clean the surface;
- apply notches with an ax or perforator;
- treat with a special primer that enhances adhesion;
- add a plasticizer to the plaster, which increases the elasticity of the solution.
Adhesion properties of paints and varnishes
The ability of coatings to adhere depends primarily on the surface on which they are used.
- Adhesion reaches its maximum values when processing rough materials. This is due to the fact that for a smooth surface, the area of contact with the paintwork material will become much smaller.
- Another factor is the structure of the processed material. So, when coating a porous surface of paintwork materials, the composition penetrates into the base. Therefore, it will be possible to remove a layer of paint or varnish only if it is possible to break the molecular bonds of the coating or base (for example, as when grinding).
In addition, the adhesion ability is increased by various modifying additives that are used in the manufacture of paints and varnishes:
- organosilanes that prevent corrosion and have a hydrophobic effect;
- organometallic substances acting as catalysts for chemical processes;
- polyesters;
- various fillers and ballast substances (for example, talc);
- esters of rosin and phosphoric acid;
- polyamide resins;
- polyorganosiloxanes.
Adhesion to concrete
Currently, concrete is one of the most famous and widely used building materials. It is concrete slabs that most often act as the foundations of walls, ceilings and floors in an apartment. Due to the smoothness of the surface of these boards, the adhesion of various finishing compositions to them is often very weak.
To ensure good adhesion to this material, many points must be considered:
- Adhesion to a dry surface is several times higher than to a wet one.
- Such a characteristic of the concrete itself, as the compression limit, directly determines the quality of adhesion of various polymeric materials to it.
- The use of special compounds and primers can significantly improve the quality of adhesion of the surface to the coating.
- When applying various compositions (glue, putty, paint, plaster), the humidity and temperature of both the substrate and the air in the room should be taken into account.
- To a rough surface, adhesion is always higher than to a smooth one.
Roughness can be achieved in different ways, one of them is applying special primer "Betonokontakt" (“Betokontakt”, “Concrete contact”, etc., the name varies depending on the manufacturer). Due to the content of cement and quartz sand, the primer turns a smooth surface into a rough, reminiscent of fine-grained sandpaper.
Thus, thanks to the phenomenon of adhesion, high-quality adhesion of the coating materials to the base is ensured. Without this, paints and varnishes would immediately fall off the treated surface, it would be impossible to apply decorative finishes or plaster walls. Each type of material has a certain level of adhesion ability. At the same time, many external conditions can both increase it and reduce it.
