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Resins: The most important conditions for the successful processing of epoxy resins


Optimal storage of the original container

Storage / Shelf Life: In unopened original containers, dark and above 15 ° C / at least 2-3 years.
Resin / hardener should be stored at room temperature (20-25 degrees) for at least 12 hours, especially immediately before processing.
Only use resin / hardener as long as the best-before date has not yet passed (resins are generally less critical here than hardeners).


Open the original container and remove the components

If original containers are opened, the humidity should be as low as possible (≤ 65% is ideal). The hardeners in particular tend to react with air humidity and then lose their quality the longer or more often the contact takes place. The more often a container is opened, the more often it comes into contact with atmospheric oxygen and moisture and other components that are in the ambient air. The hardeners in particular react with all organic components in the air. Depending on the temperature and responsiveness, more or less quickly and with more or less major effects on the quality of the hardener.
When removing the components, care must also be taken not to contaminate the epoxy resin / hardener with dirty tools (brush, stirrer, mixer)



During processing, the temperature of the epoxy resin systems and the ambient temperature should ideally be around 20 ° C.
Lower or higher temperatures can make processing difficult or impossible. Among other things, however, this also depends on the epoxy resin system used. Special epoxy resin systems can be processed from 5 degrees upwards. Others require processing temperatures well over 25 degrees.
The humidity should also be as low as possible during processing (≤ 65% is ideal) and the ambient air must not be contaminated with foreign substances.Oil mist from compressors or solvent vapors in particular can have a negative effect on the curing process and thus affect the quality of the components.
Air contaminated with foreign matter can also act as a separator and affect the bond between two layers of epoxy or laminate.
For example, the connection / gluing between EP gelcoats and EP laminate can be deteriorated, sometimes seriously.


Mixing resin and hardener

Resin and hardener must be dosed as precisely as possible (+/- 2 parts), preferably by weight, only in exceptional cases by volume. The quantities should not be too small because of the corresponding tolerances (the smaller the amount of resin / hardener used, the smaller the tolerance). Quantities of> 50 g resin + the corresponding amount of hardener are ideal, weighed with a suitable digital scale and mixed in a suitable mixing vessel (to be found in the R&G shop)
The components must be mixed as thoroughly as possible. Here, too, it is advantageous not to use too small batches, because otherwise in practice there will be excess resin or hardener on the walls of the mixing vessels. Practice shows that incorrect hardening increases the smaller the mixed amount. Important: Adding more hardener than prescribed does not result in faster hardening, but only in poorer properties. Likewise, the processing time cannot be extended by adding less hardener. In the case of large deviations, hardening may not take place! Further information can be found elsewhere in our WIKI and also in the processing instructions that are enclosed with the working packs of the epoxy resin systems.

Processing time (pot life)

There are various methods for determining the processing time. It is common to use a gel timer to determine the pot life and gel time.
At R&G we measure the time for a temperature increase of 10 ° C with a resin / hardener mixture of 100 g, starting from 20 ° C until reaching 30 ° C. A mixing vessel (mixing bowl) with a tall shape is used.
The pot life information is to be regarded as a guide, as various influences can lead to deviations.

Hardening - influence of air humidity

During curing, the environmental conditions should be ideal until the epoxy resin system has cured completely. Especially when processing epoxy resin systems that are supposed to cure at room temperature, temperature, humidity, etc. must not fluctuate over a longer period of time. Constant conditions until complete curing are very important in order to achieve the highest possible component quality.


Left in the picture: curing at too high humidity, right in the picture: curing at normal humidity, in this example, mold resin P with hardener EPH 161
The ideal humidity is ≤ 65%, the less the better
In both cases, the room temperature was around 22 degrees Celsius

Explanations of the relative and absolute humidity can also be found on YouTube, e.g. in the following Video (although with regard to structural conditions, but still explained in a generally valid way).

The substrate on which the epoxy resin system is applied

The substrate, for example a negative form, regardless of the material, should generally be at least the same temperature as room temperature, i.e. around 20-25 degrees (this may differ for special epoxy resin systems, special applications).
If the substrate is to be glued, its surface must be free from any contamination and free from all components that could develop a separating effect.
If no connection with the substrate is to be established, e.g. in mold construction, then the correct processing of the release agent must be ensured.
If release agents are used improperly, this can harden the epoxy resin system (for example because the solvents contained in the release agent have not completely evaporated). Materials such as petroleum jelly or grease, which, due to their consistency, contaminate the epoxy resin system, can also lead to faulty curing.


Further processing information

Stir up

Resin components that contain fillers (gelcoat, mold resin) should be stirred thoroughly before use.
Warming up in a water bath / microwave simplifies the homogenization.
Important: fillers settle and separate!


Mixing the resin / hardener components must be done very carefully. The stirring time should be at least 60 seconds. Use a sharp-edged mixing spatula to allow scraping.
Important: Great attention should be paid to the rim and bottom of the mug. Repeated scraping with a stirring stick reliably prevents uneven mixing!

Processing conditions

a.) Temperature: The optimal processing temperature is approx. 20 ° C. A temperature increase of 10 ° C halves the pot life / doubles the reactivity.
Important: At higher processing temperatures, especially with highly reactive systems (short pot life / less than 40 min.), No larger quantities should be mixed. Since the heat dissipation from the mixing vessel is very low, the contents of the container are heated up very quickly by the heat of reaction. This can result in temperatures above 200 ° C, at which the resin mass boils off with a lot of smoke. This also applies to large-volume potting of highly reactive systems.
b.) Humidity: The humidity during processing should be 65% rel. Do not exceed humidity. Moist fillers can also have a negative effect on curing.
Important: PU resins react very strongly with air or ambient moisture, causing foaming (moisture also limits the shelf life). EP resins are accelerated by moisture!

Fillers and additives

The properties of epoxy resins can be improved by various additives. Pigments are used for coloring, fillers to increase the mechanical strength of the molding material.
We recommend the Use of ready-made pigment color pastes (Epoxy color pastes) that can be mixed in easily and without clumping.
Fillers are e.g. glass chips, thixotropic agents, cotton flakes and glass bubbles. Fillers can be spherical, rod-shaped or platelet-shaped.
When mixing the components, we recommend a certain order:

Fillers are added to the finished resin-hardener mixture, as are the R&G universal color pastes and R&G transparent colors. The mixing ratio is not changed.
Especially Metal powder allowed to not directly into the hardener component given, as they form thickenings and hard sediments in the soil.
The addition reactive additives should not in the finished resin / hardener mixture because they change the mixing ratio:
Components that Epoxy groups contained (flexibilizer, active thinner) into the resin component mixed.
Amine-containing additives such as adhesion promoters (amine silanes) are therefore allowed only added to the hardener component become.

Mixing table

A mixed table for posting at the workplace can be found here. There you will find the corresponding mixing ratio for different batch sizes at a glance.

The stirring

Small amounts up to 500 g should be stirred thoroughly by hand for 1 - 2 minutes. We recommend wooden spatulas for this.
Larger batches can only be mixed using a mixing propeller (stirrer with plastic propeller or stirrer with metal propeller) and a drill. Despite intensive mechanical mixing of the components, the bottom and the wall of the mixing vessel should be wiped off with a clean wooden slat.

Tools and mixing vessels

The vessels, devices and tools used for resin and hardener must be clean. There must also be no oil, wax or grease film on the parts. Tools used to handle release agents must be kept separate from tools used for resin and hardener. In order to further exclude the risk of contamination, resin, hardener or the mixture should be covered.