Properties of one-component installation materials
Many applications within flooring can often be carried out in the same way using different product systems. If there is the possibility to choose between one-component and two-component systems, the installer will mostly prefer to use 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, is largely unknown to most users. 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 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.
Properties of two-component installation materials
Two-component product systems consist of two reactive components exactly matched with each other and which are kept and transported separate from each other. Immediately before use, they are mixed together and then they react largely independent of external influences to produce construction material with well-defined properties. As both the components, as a rule referred to as A and B, are specially matched with each other, they produce reaction products that, when used as intended, meet the highest level of requirements. Due to the high reactivity of the individual components, the use of 2-component systems requires the strict observation of the prescribed work protection conditions! After curing, the products present no health or ecological hazards.
Basically, hydraulic setting, mineral systems (cement and calcium sulphate based dry mortars) are, just like reaction resins, 2-component systems. However, it is usually only the reaction resin systems that are grouped under the term 2-component systems. This last-named group is also restricted to the following types.
2-component polyurethanes: 2-component polyurethanes are predominantly used in a paste-consistency form as adhesives for wood flooring, resilient coverings and occasionally also for ceramic tiles. Low-viscosity versions are also used for high-performance, self-levelling compounds. Their main feature is that they have high strength and, at the same time, they are flexible. In order to achieve their full performance, it is absolutely essential to maintain exactly the mixing ratio of A to B (resin to hardener) as prescribed by the manufacturer. This mixing ratio varies according to product and is in the range between 5:1 and 10:1 parts by weight. To exclude any mixing errors, 2-component PU products are always offered in system, i.e. the manufacturer always supplies the materials in a quantity ratio matched to each other.
Often, these products are supplied in so-called combi-cans. This is a packaging unit that contains the A and B components in two chambers separated from each other. By use of appropriate methods immediately before mixing, e.g. punching through one of the chambers, the two components are combined, automatically in the correct mixing ratio, and are then thoroughly mixed. With this technique, mixing errors practically never occur.
During application, the temperature determines the recommended area of use due to two different effects. High temperatures accelerate setting and, therefore, shorten the curing time. In the same ratio, they also shorten the pot-life. The working time reduces rather less as the substrate can work to cool the applied adhesive and, therefore, delay setting. If temperature reduces the setting time e.g. by half from 24 to 12 hours, then the pot-life reduces accordingly from 30 to 15 minutes. As a rule, the shortening of the pot-life restricts the recommended maximum working temperature to 25°C. Conversely, low temperatures extend the pot-life and setting time. With low temperatures, a secondary effect also occurs: the viscosity of 2-component PU systems increases significantly with decreasing temperatures and the ease of spread deteriorates considerably. Therefore, the manufacturers often recommend a minimum container temperature of 18°C. Hence, in comparison with 1-component products, 2-component PU systems have a relatively small application window of only approx. 18 – 25°C. For the installer, this means: always pay attention to the storage temperature! If the storage temperature varies greatly from the recommended working temperature (e.g. low store-room temperatures in winter or higher interior vehicle temperatures in summer) then, before use, the containers must be given sufficient time for temperature acclimatisation. For example, a 6 kg can of 2-component PU adhesive requires approx. 8 – 10 hours in order to warm up from 10 to approx. 20°C.
2-component PU systems can differ in their resistance to saponification. Dependent on the system, use outdoors and in wet areas can therefore be possible and the relevant manufacturer’s recommendations should be observed.
Freshly applied, not yet completely dried cement levelling compounds have a very high pH value. If 2-component PU materials are applied too early onto such surfaces (which fortunately very seldom occurs), it can lead to damage due to saponification.
Epoxy resins: installation materials based on epoxy resins are exclusively offered in two-component format. They are used in low viscosity as primers for adhesives and levelling compounds (for the latter, grit-coated) as well as for resin-bonding of screed cracks. Due to their low coefficient of water vapour permeability, they also often serve as damp-proofing as a sealer-primer on damp substrates and as damp-proofing in accordance with DIBt (German Institute for Construction Technology) regulations. By mixing with suitable aggregates, high strength synthetic resin screeds and levelling compounds can be produced. In addition, they are used in large quantities for coatings and industrial flooring. In high viscosity, they are used as adhesives in heavy wear areas as well as under large and small format tiling in areas exposed to chemicals. The mixing performance is similar to that of 2-component polyurethanes: the mixing ratio between resin and hardener must be strictly maintained and therefore, also with the epoxides, many are offered in combi-cans; the ratio is product-specific and is in the range from 1:1 to 1:5. When using as a sealer-primer or for visually critical surfaces, in order to achieve optimum thorough mixing, the combined resin / hardener system, immediately before application, should be poured into a second container and mixed through once again. In this way it is ensured that inadequately mixed resin, e.g. from the corners of the original container, are also 100% blended into the mix.
The temperature properties are also analogous to the 2-component PU systems. The low viscosity products should be used at between 15 and 25°C; at below approx. 10°C, a reliable cure can no longer be guaranteed.
As primers, levelling compounds / screeds or adhesives, they can usually be used in interior or exterior locations without restriction and some special products can even be used on wet substrates. So long as the prescribed conditions are maintained, installation materials based on epoxy resin are very reliable in use.
Methacrylate and unsaturated polyester resins (MA und UP): in their basic composition,MA and UP resins are very similar. Into the resin component, a reactive synthetic resin is cross-linked with the reactive thinner that acts as the solvent; with MA resins, the reactive thinner is methyl methacrylate and with UP resins it is styrene. As the application properties are largely derived from the curing mechanism, MA and UP resins can be treated as one group. Their curing properties differ fundamentally from the polyurethane and epoxy resins with corresponding impact on the application conditions. The low viscosity resins are predominantly used for resin-bonding of cracks and joints in screeds and concrete and, in higher viscosity, also for bonding trims, strips and profiles. In addition, by adding sand, reaction resin mortars can be produced for a wide range of repairs, e.g. on concrete stairs.
MA / UP resins cure by the addition of hardener. The hardener starts the so-called polymerisation of the resin component. By reaction of the resin particles with each other, they harden. This is in contrast with the PU / E resins where resin and hardener together form the cured resin structure. Basically, with the MA / UP resins, the hardener acts as a catalyst that activates the curing process with greater or lesser speed. In use, this means that the quantity of hardener added can vary within a considerable range without the end properties of the cured resin being appreciably affected. The permissible hardener quantity lies in the range between 1 and 10% of the resin quantity, though approx. 2 – 6% is most often recommended.
Actual numerical example: the maximum possible range in the resin / hardener ratio for PU / E resins is around 10% but with MA / UP resins it is 300% or more! Therefore, mixing errors are practically excluded.
In practice, there are two particular advantages. First, at a given temperature, the curing time can be varied over a wide range. E.g. at 20°C, the pot-life of a product can be user-defined between 5 and 20 minutes. Second, with selective variation of the hardener quantity, the same pot-life can be achieved at different temperatures. Overall, this gives an extremely wide range of uses from approx. 5 to 30°C. In addition, the time-gap between pot-life and curing time, compared with PU / E resins, is dramatically shorter. An epoxy resin with 30 minutes pot-life has a curing time of between 8 and 24 hours whereas a corresponding MA / UP resin will already accept loading after approx. 1 – 2 hours and this is in both interior and exterior locations.
Disadvantages of the MA / UP resins are the intense odour and their solvent effect on polystyrene. On floating screeds, it must be determined that the material cannot penetrate into the insulation layer. Otherwise, it will dissolve the insulation and compromise its function.