Choosing a primer for construction and finishing works

Recommendation points

• Primers: types and purpose
• For concrete and stone substrates
• “Finishing” primers
• For facade work
• For wood and metal
• Trusted manufacturers
• How to make sure of quality

The building materials market is literally flooded with a variety of products, in particular, the range of primers is counted in hundreds of positions. Today we will try to understand this assortment and learn how to distinguish real primers from ineffective liquids.

Primers: types and purpose

Most primers have two purposes, both ultimately boil down to improving adhesion – the quality of adhesion between the substrate and the coating applied to it. One of the mechanisms of action is to strengthen the top layer with the formation of a sticky film on it, which acts as an adhesive. Some compounds have an additional effect – they penetrate deeply into the thickness of the porous material and strengthen it at the structural level.

Most construction primers are universal in their application, based on an acrylic binder or a polyvinyl acetate suspension. Water acts as a solvent in such compositions, which facilitates the preparation of solutions of different concentrations for more economical consumption. Primers can also have a mineral filler, due to which the crust becomes rough after drying, as well as all kinds of additives: corrosion inhibitors, surfactants, dyes to control the uniformity of application, antiseptics and others. Virtually all water-borne primers do not contain volatile solvents, which makes them suitable for indoor use.

There are also special primers with a number of specific functions. Typically, they are designed to handle complex materials between finishing steps. Such primers are based on various complexes of alkyd, epoxy and formaldehyde resins, respectively, organic solvents such as alcohols, toluene or ethyl acetate are used to obtain the required consistency. Such compositions are used exclusively in exterior decoration, less often in the process of overhaul. The main purpose is to increase adhesion before applying paintwork materials or waterproofing, as well as to reduce consumption and normalize the absorption of finishing and insulation materials.

For concrete and stone substrates

When performing “wet” construction and repair work, primers are used everywhere. When pouring all types of screeds, as well as when applying plaster on walls and ceilings, the properties of cement, cement-polymer and gypsum binders are usually insufficient. The primer in such cases works as a highly diluted adhesive, effectively binding dust and strengthening the surface. When redissolved, the adhesive does not lose its properties, contributing to the formation of additional polymer bonds along the entire contact plane between conventionally homogeneous layers, due to which the swelling and delamination of materials is almost completely eliminated, even under extreme loads.

Primers for rough finishing works are commonly called “Betonkontakty”, under which they are produced by some well-known manufacturers. The composition is an aqueous dispersion of acrylic and its copolymers, sometimes calcium or sodium silicate additives are added to improve the strength properties. Almost all primers of this type have a mineral filler in the form of quartz sand, it is necessary to fill the pores of loose materials and additionally strengthen the base structure.

As a rule, Betonkontakt is supplied in the form of a concentrate and, depending on the density of the base, can be diluted up to 20 times with pure water. Application is carried out mainly in bulk – for such primers, high-quality impregnation is extremely important for a long time before drying. Walls and ceilings are treated with a roller in small areas, all the while keeping the surface moist. The duration of this method of application can be up to 1-2 hours..

“Finishing” primers

The most common class of primers is intended for the preparation of walls before puttying, wallpapering or coating with water-dispersible paints, that is, before finishing. Such primers simultaneously perform two functions: they impregnate all layers of the rough finish and hold them together, preventing the formation of cracks, and also form a film that promotes better adhesion between the base and the finish. In this case, the primers work in such a way that the separation of the top layer is possible only forcibly as a result of directed mechanical action.

Most primers for interior use are based on acrylic water dispersion or vinyl acetate suspension. There are also formulations with the addition of modified silicone, which contributes to quick setting and the formation of a durable hydrophobic surface. Such compositions are ideal for use before wallpapering, due to the silicone component, the removal of the cloths in the future is facilitated.

The main difference between internal primers and concrete contact lies in the reduced concentration of the polymer binder. Another characteristic feature is a high variety of all kinds of additives and an almost complete rejection of the mineral filler, although in exotic options the presence of mica or marble dust is possible. Primers of the “light” class are distinguished by their ability to maintain natural gas exchange of materials and provide additional properties such as resisting the formation of mold and mildew, penetration of moisture into deep layers or improving adhesion for a specific type of finish coating.

For facade work

Almost any exterior finish done with the “wet” method is not complete without the use of primers. Moreover, the primers are special and, depending on the regulations of the finishing technology, they can only be used between certain layers of the facade cake.

A significant part of the facade primers are based on aqueous suspensions of polymers; they differ from universal primers for interior work only by a relatively coarse quartz filler and various additives, because of which they cannot be used indoors. Additives are added to give the material impregnated with the primer additional resistance to acids and alkalis, as well as to enhance the adhesive properties of the base.

Recently, compositions based on synthetic resins in organic solvents, including two-component ones, are gaining popularity. The main field of application of such a primer is as a primer before applying a coating or overlay waterproofing. Another purpose is the preparation of concrete surfaces before painting and the processing of natural stone to increase frost resistance.

For wood and metal

Primers used to prepare wood and metal structures for painting are fundamentally different from building primers. First of all, the fact that all of them, with rare exceptions, are based on alkyd or polyurethane resins on an organic solvent. In essence, these are paints of the same type that are planned to be applied during finishing, but without film-forming agents and with a variety of additives..

Metal primers contain a wide range of corrosion inhibitors, and sometimes also rust converters, which allows their application without preliminary surface cleaning. It is also practiced to coat metal structures with passivating and phosphating primers – a kind of analogue of cold galvanizing for local application. Lead and iron mines are often used as filler in metal primers, but not as pigments, but for passivation of structural steel.

Wood primers have a less viscous consistency and penetrate well into wood vessels. Due to this, the length of the polymer chains that form when the paint dries increases. It is due to the high variety of paints for wood, most of which retain the texture or texture of natural wood to the detriment of the density and strength of adhesion, and preliminary impregnation of the surface with a special primer is required, but its type must be compatible with the base of finishing paints.

Trusted manufacturers

Knauf, Weber and Ceresit are deservedly considered the most responsible suppliers of primers and other construction chemicals on the CIS market, as well as another Henkel subsidiary, Moment. The range of these manufacturers has formulations for any application that may be required in civil engineering, however, these brands only supply one or two types of special and facade primers. As a rule, these are universal compounds for increasing the frost resistance of tile cladding or the device of the base reinforcing layer of wet facades..

For finishing facade work, use the primers recommended by the manufacturer of the finishing coating used. For a long-lasting facade paint application, it is better to give preference to Dufa, Tikkurila or Caparoll products with the appropriate base formula. For applying decorative plaster, it is allowed to use universal compounds, you can also give preference to deeply penetrating facade primers Bostik, Baumit or Polirem.

As for primers for alkyd enamels, it is better to purchase them of the same brand as the paint itself. Due to this, the maximum compatibility of the compositions of soil and paintwork materials is ensured, however, the instructions should provide for the joint use of materials of certain brands.

How to make sure of quality

One of the problems of the building materials market is considered to be the dominance of counterfeit products of common brands, as well as products of little-known brands, which are positioned as full-fledged analogues of lower cost, but in fact do not perform the assigned functions. To guarantee the durability of the finish, you should purchase only high-quality compositions that have been tested by time and the experience of other craftsmen..

In principle, the effectiveness of a primer can be verified visually. To do this, you need to pour a small amount of it into a plastic bag and wait until it dries completely. The resulting film is easily separated; its thickness and density can be used to judge the concentration and strength properties of the polymer complex used to create the suspension. It is clear that this does not apply to primers based on synthetic resins, their effectiveness can only be verified by real operating experience..