First, it is more difficult to meter and mix the resin and hardener. The cold resin and hardener do not flow through the dispensing pumps easily and the thicker material clings to the surfaces of the pumps, containers and mixing tools. Colder and thicker resin and hardener take much more time and effort to blend thoroughly. The potential for inaccurate metering and incomplete mixing, compounded by a less efficient chemical reaction, greatly increases the possibility of a deficient bond. Second, the epoxy is much harder to apply.
Cold temperatures make it much more difficult to coat and wet-out surfaces with epoxy.
In coating applications at low temperatures, the epoxy mixture will not flow out as easily resulting in thicker, uneven coats that require more sanding to achieve a smooth finish. In bonding applications, the thicker epoxy may not wet out or penetrate porous surfaces enough for a reliable bond. Third, air bubbles may be introduced during mixing or application and held in suspension due to the chilled epoxy's increased viscosity. Air bubbles reduce epoxy's strength in a bond and a coating's effectiveness as a moisture barrier. In addition, air bubbles show through clear coating applications.