WHY DOES EPOXY HAVE AN OPEN TIME?
Epoxies like Sika® MB and Sika® MB Redline are typically two part epoxy resins, and 100% solids. The curing agent (called hardener) reacts with moisture and carbon dioxide in the atmosphere in order to create something called an amine blush. This blush will result in a waxy usually invisible layer and will determine the limits of your open time. In worst case scenarios, a white/yellow layer will be visible on top of the epoxy.
WHAT ARE THE RISKS?
The blush will create an oily and sticky surface possibility resulting in several issues:
- Transfer to the second coat
- Delamination as the amine blush will work as a bond breaker
- Difficulty in re-coating
- Water spotting
WHAT SHOULD YOU DO IF YOUR OPEN TIME EXPIRES?
Lightly sand the epoxy to provide a good texture.
Clean contaminated surface with approved solvent such as acetone, MEK or Xylene.
Allow all solvent wipe residues to completely evaporate, flash off and dry before the next step.
- Cool, humid conditions are the biggest concern. The cold weather will slow the reaction; in addition the humidity will give perfect condition for faster development of amine blush.
- In warmer weather where the curing cycle is shortened, amine blushing tends to happen more inconsistently.