HOW TO USE EPOXY RESIN: TRICKS AND GENERAL
GUIDE.
Definition: Epoxy resin is a two-component thermo-hardening liquid polymer.
Apart from the “technical” definitions, epoxy resin is a liquid product which, if exposed to a minimum temperature of 10-15°C [50-59 F], begins to catalyse and then solidifies.
Here are some “fundamental” points for who approaches this product for the first time.
How do you dose resin?
Since it is a two-component product, the package features 2 containers, one with resin “A” and the other with hardener “B”.
Equip yourself with an electronic scale to weigh the grams and with a container to mix the liquids
- Put the amount of A you think you need in the container, trying to get a round number in grams (e.g. 200 gr [0,44 lb]), this will make it easier to count how much hardener to add;
- Each product features on the container of B (or even on both) the usage ratio;
- Let’s make an example with 100A: 60B. Multiply the grams of A previously weighed (200g [0,44 lb]) by 60 and then divide by 100, the result will indicate the grams of B to be added.
Practical example (ratio 100: 60)
40 gr [0,08 lb] component A. how much component B should I add?
Solution A 40/100 = 0.40 A 0.40×60 = 24. This means 24 gr [0,05 lb] of B.
This formula can be used for any usage ratio, 100:50, 100:30, etc.
How to prepare the resin?
After having been accurately measured, the resin must be mixed in an irregular way (so, not always in the same direction) for at least 2-3 minutes. This passage is fundamental, since if you mix it only for a few seconds, the resin won’t be well homogeneous at the molecular level, and therefore it will remain soft/opaque in some parts
How much does the resin harden?
Hardness depends on the formulation, the resting time and the catalysis temperature.
Furthermore, the mechanical resistance 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 until it becomes like “hard” plastic (let’s say “plexiglass-like”)
How long does it take for epoxy resin to solidify? Is it possible to accelerate hardening?
Also in this case, it depends on the formulation and on the temperature.
However, since it is a “THERMO-HARDENING” polymer, the more it is exposed to heat, the faster catalysis is.
As a general rule, every 10°C [50 F] more, the catalysis time is reduced by half.
Example
20°C [68 F] = 3h00’
30° C [86 F] = 1h30’
40°C [104 F] = 0h45’
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 up castings over 1 cm [0,39”] thickness. Resin may in fact heat up too much due to the mass effect (which is explained in the guide)
“Mass” effect.
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 [0,39”]). The A molecules, indeed, release heat when they bind with the B molecules, and it is immediately which is immediately dispersed in minimum thicknesses. When the casting thickness is instead higher than 1 cm [0,39”], the heat is dissipated more slowly, so 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 yellow?
Any resin (even with “advertised” UV filters) sooner or later, if exposed to sunlight, will tend to change colour, turning towards an amber shade. It may take a few weeks or many years depending on exposure to sunlight (outdoor it will yellow sooner), on the thickness of the resin (the thicker it is, the more it will be visible) and the type of colouring. For example, if the resin is coloured in a “strong” tone such as red or black, the yellowing won’t be visible… while if it is white or pink, you will detect it sooner.
Resins usually feature reduced-yellowing characteristics and can therefore be used for manufactured products that should not change colour for several years (if stored indoor), such as paintings, tables or jewellery.
How to remove surface opacity or small ripples that appeared right after solidification?
These surface opacities (especially in the cold season) are the result of the effect of ambient humidity, which creates a patina on the surface of the casting. At first you won’t notice it, but as soon as it solidifies, you will see matt auras and even a crinkled film, in some points.
To avoid this, there are several strategies:
- Working in a low humidity (dehumidified) or warm environment;
- Heat up 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 little care.
Resin (according to the quantity you have prepared, because of the “mass” effect) may in fact need a few dozen minutes before heating up. It should be checked every 5 minutes and as soon as it reaches 40°C [104 F] (that is when it is warmer than our hand), it can be applied. In this way, a part of the molecules has already reacted and it is therefore less vulnerable to ambient humidity. But be careful not to wait too long before pouring, otherwise it may solidify in the container! - It would be a good rule not to apply it in the evening or when it rains (as the ambient humidity increases);
- Do not apply on surfaces that still retain moisture such as, for example, wet concrete or undried wood.
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