HOW TO USE THE EPOXY RESIN. TRICKS AND GENERAL GUIDE.
Definition: The epoxy resin is a two-component liquid polymer, thermo-hardening.
Beyond the “technical” definitions, the epoxy resin is a liquid product which, if exposed to a minimum temperature of 10-15°C, begins to catalyze thus becoming solid.
Here are some “fundamental” points for those approaching this product for the first time.
How do you dose the resin?
Being a two-component, you have 2 bottles at your disposal, one containing resin “A” and the other hardener “B”.
Equip yourself with an electronic scale to weigh the grams and with a container to combine the liquids
- Put the amount of A that you think you need, trying to get a round figure in grams (e.g. 200g), this will make it easier to count how much hardener you add.
- Each product indicates the application ratio on the falcon of B (or even on both).
- Let’s take an example with 100A: 60B. Multiply the grams of A previously weighed (200g) multiply by 60 and then divide by 100, to obtain grams of B to be added.
Practical example (ratio 100: 60)
40g component A. how much component B should I add?
Solution à 40/100 = 0.40 à 0.40×60 = 24. That is 24g of B.
This formula can be used for any employment ratio, 100:50, 100:30, etc.
How is the resin prepared?
Once dosed accurately, the resin must be mixed in an irregular manner (therefore not always in the usual direction) for at least 2-3 minutes. This part is fundamental, since if it is mixed only for a few seconds, at the molecular level it will not be well homogeneous, and therefore it will remain soft / opaque in some parts
How hard does the resin become?
The degree of hardness depends on the formulation, the resting time and the catalysis temperature.
Furthermore, the mechanical strength of the resin continues to increase up to 4-5 days after application.
So after 24 hours it may still seem soft, but in the following days it will continue to harden up to become like a “hard” plastic (let’s say “plexiglass-like”)
How long does it take for epoxy resin to solidify? Can the hardening process be accelerated?
Also in this case it depends on the formulation and on the temperature.
However being a “THERMO-HARDENING” polymer, the more it is exposed to heat and the faster the catalysis is.
As a general rule, every 10°C more, the catalysis time is reduced by half.
To accelerate the catalysis, it is therefore sufficient to keep the casting close to a heat source (even a simple radiator). Be careful, however, not to heat castings over 1 cm thick. In fact the resin could heat up too much due to the mass effect (which is explained in the guide)
This term is used to describe the exothermic phenomenon (i.e. heat release) that occurs when the resin is poured in high thicknesses (greater than 1 cm). In fact, the A molecules, by binding with the B molecules, release heat, which is immediately dispersed in the event of minimal thicknesses. When instead the thickness of the casting is higher than 1 cm, the heat is dissipated more slowly, then the casting starts to heat up.
This heating further accelerates the reaction, which causes the temperature to rise even more. For this reason it is necessary to avoid pouring too much resin all at once, in order to prevent it from “cooking” (creating cracks, bubbles and darkening).
Does the resin turn yellow?
All resins (even with “advertised” UV filters) sooner or later, if exposed to sunlight, will tend to change color, turning towards an amber shade. It may take a few weeks or many years depending on exposure to sunlight (it will turn yellow on the outside first), on the thickness of the resin (the thicker it will be the more you will see it) and the type of coloring. For example, if the resin is colored in a “strong” color such as red or black, the yellowing will not be seen… while if it is white or pink, you will notice it first.
Resins are usually characterized by low yellowing and can therefore be used for manufactured products that are required not to change color for several years (if kept inside a house), such as paintings, tables or jewelry.
How to eliminate superficial opacities or small ripples formed when solidified?
These superficial opacities (especially in the cold season) are the result of the effect of environmental humidity, which creates a patina on the surface of the casting. At first it is not noticed, but as soon as it is solidified, you can see opaque halos and even a crinkled film, in some points.
To avoid this phenomenon there are several strategies:
- Working in a low humidity (dehumidified?) or heated environment;
- Heat the 2 components before pouring them (for example by holding them over a radiator);
- Mix the resin with the hardener and apply it only when it starts to heat up (so that the reaction starts when it is still in the container). This operation is essential, but requires a minimum of attention
In fact the resin (based on the prepared quantity, due to the “mass” effect) may need a few tens of minutes before heating up. It should be checked every 5 minutes and as soon as it reaches 40°C (that is when it is warmer than our hand), it can be applied. In this way a part of the molecules have already reacted and it is therefore less vulnerable to environmental humidity. But be careful not to wait too long before pouring, otherwise you risk solidifying in the container!
4. It would be a good idea not to apply in the evening or when it rains (as the environmental humidity increases).
5. Do not apply on substrates that still contain moisture such as, for example, fresh cement or not dried wood.
How is the resin polished?
There are several methods. Much depends on the size and regularity of the surface to be polished.
The larger a surface (or irregular, such as a jewel or a miniature), the better it is to use spray paint. The ideal is the transparent polyurethane spray that is used for lacquering furniture. If it is not available (as an easy-to-find fallback) you can use the transparent acrylic spray that is found at the hardware store. However at least 2-3 sprays are necessary for a good finish.
The method that surely guarantees the best aesthetic effect is manual polishing with abrasive paper (up to grain 1500) and then concluding with the classic “polish” (i.e. the polishing paste) that is used to polish the plastic of car headlights. This technique however requires experience and an orbital polishing machine, otherwise scratches and irregularities will always remain. Recommended only for professionals with adequate equipment, and for objects that are not too large and fairly regular.
Another method is to apply with a brush (or by casting) an epoxy resin finish (after having polished up to grain 400).
The advice is to wait for the resin to become more viscous (letting it rest in the container after preparing it) and then reach a consistency close to “honey”. At that point you can start applying it with a brush (or by casting, if you want to get a mirror effect).
How do you eliminate air bubbles from the resin pastes?
Although it is necessary, to eliminate 100% of bubbles, de-gasifiers are necessary, there are some tricks that can help us to minimize the presence of bubbles in the creations.
- mix the resin for a longer time but in a more delicate way
- when the resin is poured, try not to let it fall from above, but pour it closer and closer to the possible surface
- once the resin has been mixed, let it rest for a few minutes, to make the air bubbles rise again
- once poured, pass a heat source (heat gun or flame, NOT hair dryer) to make burst the bubbles on the surface
Once the resin has hardened, can it be sanded, cut or pierced?
Certainly. Once it is well catalyzed (24h-48h) depending on the catalysis temperature, the resin can be processed as normal hard plastic.
With what can the resin be colored?
In practice with anything. Including powders, dirt, metallic pigments. As long as the coloring agents are “dry” (for example powders or sand) there are no problems (as long as they are perfectly dry).
When instead you want to add colors in paste or liquid, you need to check that they are compatible with epoxy resins.
If they are not compatible (for example enamels or tempera), only a few drops can be added, as an excess dosage could compromise the mechanics of the resin and its lucidity (for example, it can make it porous or sticky).
If we summarize… the Three Golden Rules
Given that it is difficult to remember all the tips, for beginners we recommend focusing on 3 fundamental points:
- Correct dosing and mixing with electronic scale and mixing for at least 2 minutes.
- Application at a minimum temperature of 20°C avoiding damp application areas (or surfaces) (if you are not sure of the humidity, allow the resin to warm up before pouring it, as described at the beginning of the guide).
- use a heat gun / flame to eliminate bubbles on the surface.