Many applications within flooring technology can often be carried out technically the same using different product systems. If there is the possibility to choose between one-component and two-component systems, the installer will mostly prefer to one-component products. They are more user-friendly as they do away with the mixing process. Mixing errors are excluded and there is no problem in the use of part quantities. The result of this user preference is that newly developed products are mostly planned as one-component and system recommendations are based on one-component products where possible. One-component and ready to use are, therefore, often considered as synonymous.

Installation materials, depending on their intended use as, for example, primers, levelling compounds or adhesives, are composed of different classifications of substances. The result is that different products, even if they are all offered as ready to use, demonstrate completely different drying and setting characteristics. The drastically different effect of relative humidity on the different groups of materials, that is clearly unknown to most users, is stated here by way of example. Ignorance of the typical drying and setting performance of materials, under unfavourable construction site conditions, can quickly lead to damages, generally unexpected as far as the user is concerned as he has worked with ready to use products.

Below are described the most important materials classifications for use in flooring technology with their typical product groups as well as their application properties. Practice shows that knowledge of the underlying materials classifications for the installation materials is not only of academic interest but can also be helpful in the assessment of problematic installation situations and in avoiding damages and claims.

1-component dispersion products: dispersions are by far the most used non-mineral installation materials. They comprise of fine polymer particles suspended in water and often fillers, such as chalk, are also added. The area of use ranges from almost water-thin products such as dispersion primers through to thick-paste products like dispersion adhesives or acrylic sealants. They set physically in that the water content evaporates or is absorbed into the substrate. Most often, both factors apply. They harden in that they dry (the term “dry” appears, in this case, quite trivial. That is it completely wrongly understood and used is shown below in the section on reaction resins). Basically: 1. the higher the temperature, the faster the drying 2. the higher the relative humidity, the slower the drying. This drying performance is generally known.

However, a potential damage situation also occurs, although fortunately only on a small scale, if resilient coverings are to be bonded in cellar areas with dispersion adhesives. The minimum temperature of 15°C required for installation is often barely achieved, at floor level it falls below, and the air exchange, that can accelerate the drying, is lacking. Therefore, the relative humidity moves quickly up to the critical level of 75% or above. “Complaints”, that the adhesive is still not adequately aired after 4 or even 8 hours are the result, but in the view of the adhesive manufacturer, they are unjustified due to inadequate climatic conditions in the area.

1-component solvent-based products: they are used either low-viscosity as solvent-based primers or high-viscosity as solvent-based adhesives, predominantly as wood flooring or contact adhesives. Due to the apparent risks from the point of view of workplace protection and ecology, they should fundamentally be viewed as problematic and should, where technically possible, be replaced with solvent-free products. Like the dispersions, they harden physically through evaporation of the solvents, i.e. they dry. The higher the temperature, the shorter the drying time. The temperature dependency is less marked than with water-based dispersion products. Therefore, at lower temperatures, they offer greater usage potential, a criterion that can be crucial to the selection of products, e.g. when bonding skirtings in low temperature areas (stairwells). The drying is achieved regardless of the level of relative humidity.

1-component polyurethane: 1-component polyurethane is used in low-viscosity as primers and in high-viscosity as wood flooring adhesives. They harden through reaction with water from the surroundings by formation of gaseous carbon dioxide. Therefore, they are totally dependent on a minimum air moisture content (approx. 40% relative humidity).

In their use as primers on dry surfaces, it is especially important to note that the required moisture for setting will predominantly be taken from the surrounding air. Thus, the primer will not cure consistently from inside outwards but gradually from the upper surface. The thickness of the coat applied is, therefore, a quite decisive factor for satisfactory results. If the primer-coat is too thickly applied, it will harden on its upper surface and the transfer of moisture through to the base of the coat will be arrested. As a result, the complete cure-time can be drastically extended – doubling of the cure-time due to exceeding the recommended thickness is then not unusual. If the primer is used as a moisture-barrier, usually requiring a two- or three- coat application, then the quantity prescribed by the manufacturer can never be applied in a single coat. The uncontrolled complete cure then not only extends the hardening time but also the effectiveness as a moisture-barrier can be considerably impaired, e.g. due to formation of bubbles.

Although 1-component polyurethanes essentially require moisture for curing, too high an air humidity can also be damaging. With moisture above 75% the cure is so fast that the carbon dioxide given off cannot emit as a gas quickly enough from the primer film. The carbon dioxide stays trapped within the primer-coat and the result is that gas expansion forms as bubbles. Negative effects resulting from low air humidity occur very seldom as, in these cases, the residual moisture from the substrate is drawn out as a curing aid.

In use as a wood flooring adhesive, the air humidity plays practically no role in the curing process as the substrate and the wood contain sufficient moisture to achieve a reliable cure.

It is little known that polyurethane adhesives can also react with other materials from the surroundings. In particular these include ammonia (in smoked oak!) and alcohol. Whilst the effects of these concurrent reactions are insignificant in the case of 2-component PU adhesives, due to the relatively high hardener content, they can lead to disruption of the cure-process in 1-component polyurethanes – fortunately, these occur very seldom in practice. The result is complaints because the adhesive stays permanently soft. A problem that is often blames on “faulty” adhesive although the cause is solely the unsuitable application conditions. If wood flooring is bonded with 1-component PU adhesive, then alcohol-based cleaning agents should never be used at the same time; once the adhesive is fully cured, this restriction no longer applies.

Silane modified polymers (1-component MS / MSP): these systems are used as wood flooring adhesives and as damp-proofing sealers. In use and composition, they are very similar to the 1-component PU adhesives. Like these, they harden by reaction with moisture from the surroundings. As reaction products, they produce small quantities of methanol that evaporate immediately into the surrounding air. With this materials group, therefore, bubbles cannot occur. As even with relatively dry wood flooring (e.g. 5% moisture) the existing wood moisture is more than enough for a reliable cure, the use of SMP adhesives is practically unaffected by the ambient moisture. The temperature influence is the same as with polyurethanes. The higher the temperature, the faster is the adhesive.

Due to the chemism of the cure reaction, the concurrent reactions as described for 1-component polyurethanes are excluded. Therefore, the restrictions with regard to smoked oak and alcohol-based cleaning agents do not apply for SMP systems.

Silicones: silicones are used almost exclusively as flexible mastic sealants, predominantly in connection with natural stone and ceramic tiles. In principle, they cure (1) using the same mechanism as SMP adhesives: moisture from the surroundings reacts with the silane groups by separating off the cross-linking agent. As with all SMP adhesives, this can be methanol; most silicones harden by separating off acetic acid, easily recognisable from the characteristic odour. This reaction is dependent on temperature, consequently silicones also react quicker with increasing temperatures. Even more important is the moisture content of the air so that, in very low humidity (< 30 RH) the reaction can be very greatly retarded. This retardation is problematic at unacceptably low temperatures for flooring work (< 10°C) and at the stated low humidity. As a rule, these conditions are only met by the tile-fixer on construction sites. With increasing temperature and air humidity, the sealant “picks up” again and cures in the fullness of time.

In Table 1, the described curing mechanisms, together with the most important influencing parameters, are collectively shown. All in all, the reputation of the one-component and, therefore, ready to use installation materials as reliable working products is absolutely justified. That the term “ready to use” cannot be equated with “no brainer” is something that the instructions should clearly illustrate. In cases of doubt, the details on the container or in the Product Data Sheet provide further, valuable notes for successful work results.

(1) As the end product is rubber-like and soft-elastic, the term “hardening” is misleading.

Influencing parameters for 1-component materials
Materials Group Typical Product Groups Drying / Setting Process Important Influencing Factors during Application
Dispersions Primers, Adhesives, Sealants, (Smoothing Compounds) Water evaporates Temperature, rel. humidity
Solvents Primers, Adhesives, Contact Adhesives Solvent evaporates Temperature
1-component Polyurethanes Primers, Adhesives, (Sealants) Reaction with moisture Temperature, rel. humidity, ammonia
Silane Modified Polymers Adhesives, Sealants Reaction with moisture Temperature
Silicones Sealants Temperature, rel. humidity Temperature, rel. humidity


Dr. Norbert Arnold - Technical Product Services Manager