This may be due to Amine Blush or Blooming.
Most epoxy resins that have a long working time may be prone to blush or blooming. Due its long open time, UltraCast XT is susceptible to Amine Blush1 and Polymer Bloom2 under the following usage conditions:
- high humidity
- low ambient temperature (15°C or below)
- draughty or windy conditions including air-conditioning.
To avoid this effect from occurring it is recommend the resin component (Part A) is pre-warmed before mixing with the Hardener. The temperature and humidity of the working area should be kept as consistent as possible while the resin is curing.
1 Amine Blush is a sticky, waxy or oily appearance on the surface of cured epoxy. It can also be spotty, milky or salt-like. This deposit is water soluble and can be wipes/scrubed away with warm, soapy water.
2 Polymer Bloom is caused by the segregation of additives from the polymers which migrates to the surface.
Do not use solvents like acetone or mineral spirits to remove the blush. Using a solvent may worsens the problem, spreading the blush around and possibly embedding it into the cured resin.
Blush can prevent additional coats/layers to stick to your work. See removal above.