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 (Image 1)

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 (Image 2), 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 (Image 3).

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.

The most important properties of the product types presented are summarised in Table 1. This shows that 2-component reaction resin systems, dependent on the underlying resin type, have many common features but also, in part, they have drastically different properties. If these characteristics are taken into account in the usage, then the full potential of this versatile product group can be utilised in practice.

Materials Group Typical Product Groups Exterior Use Recommended Temperature Range Mix Tolerance
2-Component Polyurethane Resins Adhesives, Levelling Compounds, Coatings restricted use 18 - 25 °C max. 10 %
Epoxy Resins Primers, Damp-Proofing, Adhesives, Levelling Compounds, Coatings possible 15-25 °C max. 10 %
Methacrylate / Unsaturated Polyester Resins Screed Repairs, Adhesives possible 10-30 °C 300% and more

Table 1

Author:

Dr. Norbert Arnold - Technical Product Services Manager