Handling, Measuring and Mixing Epoxies
WHAT IS A MIX RATIO?
Mix ratio is the ratio of epoxy to hardener for a given resin system. Usually given in the format of quantity of epoxy to quantity of hardener, it can be measured by either volume or by weight. All our systems are two part, liquid, thermoset epoxy resins in which an epoxy component is mixed with a hardener to create a chemical reaction. This chemical reaction results in a rigid plastic. It is crucial that the two parts are mixed at the exact mix ratio or an improper cure can occur and cause sub-optimal mechanical or aesthetic properties.
HOW MUCH MIXING IS REQUIRED?
In order for the epoxy to cure properly, a thorough mix is required. Improper mixing, along with mixing at an improper ratio, are the two most common mistakes when working with epoxies. While mixing be sure to scrape the sides and bottom of the mixing container with the mixing tool and mix until the two parts are completely uniform (1-2 minutes for small batches). Usually a tongue depressor is sufficient when mixing 16 oz or less. A larger paint mixing stick (1-2 inches wide) is more efficient when mixing quantities greater than 16 oz.
WHAT IS EXOTHERM?
The chemical reaction between an epoxy resin and its hardener is exothermic, meaning heat is created as a by-product of the reaction. Since heat is also an accelerator for the reaction, over time it will eventually cause the mixture to reach a critical temperature at which the resin will solidify rapidly. The amount of time to reach the onset of an exotherm is given by the GEL TIME and is often referred to as POT LIFE. Usually the greater the amount of mixed resin in a cup, the easier it is for the mixture to reach its critical exotherm temperature. Great care should be taken not to leave large amounts of resin in a bucket beyond its gel time as it could represent a dangerous fire hazard.
WHAT ARE THE AMBIENT TEMPERATURE EFFECTS ON THE RESIN?
In general your ambient working temperature will have an effect on both your gel time and cure time. The higher the ambient temperature, the shorter your gel time will be, but the faster your cure time will be. Try to select an ambient temperature that is applicable to your working time and cure time needs. Working in cold extremely environments (less than 40°F) should be avoided.
WHAT IS BLUSH AND HOW DO I REMOVE IT?
Blush is usually observed as a greasy or tacky surface on a coating. It is usually formed during times of high humidity and/or cold temperature. It can be removed by cleaning the surface with soap and water. A final cleaning with a solvent (denatured ethanol or rubbing alcohol) should leave a smooth, non-greasy finish. Always remove blush before applying additional coats.
WHAT ARE THE APPROPRIATE SAFETY TECHNIQUES WHEN WORKING WITH EPOXIES ?
All reactive chemicals, including epoxy resins and hardeners, are sensitizers; meaning susceptible individuals can become allergic to the material after prolonged direct exposure. Always wear chemical resistant, disposable gloves and eye protection. Since wrists and forearms are most susceptible to sensitization, long sleeves and long gloves usually provide adequate protection. Always work in well ventilated areas but if this is not possible wear an appropriate respiratory mask. Although most epoxy formulations are low to zero-VOC, a slight amine odor may be irritating to some users and a respiratory mask can be worn in those instances.
Be sure to clean any uncured epoxy or hardener off of the skin immediately with a waterless hand cleaner (GOJO or citrus oil-based cleaners) as the epoxy or hardener may cause irritation of the skin, then thoroughly washed with soap and water. NEVER use solvents to remove epoxy from the skin. Acetone should be avoided with all epoxies as it will act as a carrier of sensitizers directly to the blood stream and increases the chances of an allergenic response. Solvents like denatured alcohol or rubbing alcohol can be used to clean tools and work areas while wearing chemical resistant gloves.