Water Based Epoxy Coatings

Dr. Riadth Shalash

Epoxy resins are widely used as an advanced protective coating for various substrates, due to their high chemical and corrosion resistance properties.

In response to ever changing environmental regulations, demands are being placed on epoxy suppliers and formulators towards environmentally friendly coatings, i.e. lower solvent level or solvent-free coatings, thus allowing the end user to comply with VOC regulations.

In the past 10 years, significant advances has been made in the field of water based epoxy coating systems, which as a result,  are now gaining acceptance in the market. The main advantages of water based epoxy coatings in comparison to solvent-based are:

  1. Better adhesion to damp substrates, including fresh green concrete.
  2. Good acceptance of damp filler such as sands, cements, and oxides.
  3. Lower toxicity and non-flammability.
  4. No hygiene problems due to contact.

No cost in clean up or dilution, because water is used.

Epoxy resins are generally hydrophobic in nature and to render them water borne, there are two approaches: -

  1. Chemical modification of structure.
  2. Emulsification.

The approach to chemical modification of structure is by reacting an epoxy-free radical with a growing hydrophilic polymer, which leads to formation of a water dispersible graft polymer.

The other approach to water dispersibility is by emulsifying the epoxy resin and hardener with a suitable surfactant, in which the resin and harder are effectively separated from water. These systems stay stable until they are mixed together, at which stage cross-linking reaction starts, which leads to film formation.

  1. Water based epoxy coatings are finding increasing applications in many fields: -
  2. Waterproof coating for inside and outside tanks, basements and substations.
  3. Repairing spalled concrete by using in admixture.
  4. Gloss walls and floor coatings, which resist high pressure cleaning in food-processing plants.
  5. Exterior textured and flexible coating over pavements paneling of glass-reinforced and pre-cast concrete.

Due to their environmental acceptability and economic attraction, water based epoxy coatings have a promising future matched against solvent-based coatings in performance, due to the research and development efforts which have improved their properties.