The main difference between polyurea and polyurethane coatings, and why Polyurea is more suited for Water facilities and permanent immersion.

The key to understanding when to specify polyurethane vs polyurea two-component 100% solids systems is determined by the features and limitations of the two technologies.
Understanding the chemistry behind it helps to explain these features and limitations.
The following table shows the basic materials used to formulate a polyurea, polyurethane and hybrid (Blend of both). Products/Materials are generally divided into these three categories.


Resin Components Polyurea Hybrid Polyurethane
Primary Polyether amine Polyether amine / Polyether Polyol Polyether Polyol
Extender Aromatic or aliphatic Diamine Aromatic or aliphatic Diamine / Glycol Glycol
Catalyst  None  Yes  Yes


The key difference is the catalyst. The reaction of polyurethane is too slow and requires a catalyst to accelerate the reaction.
The three reactions below are the reaction of Isocyanate with Polyol (polyurethane), the reaction of Isocyanate with Diamine (Polyurea) and the reaction of Isocyanate with Water (Unwanted reaction).
The catalyst accelerates the unwanted reaction of Isocyanate and water.
The polyurea has a higher amount of H present. The increased amount of H-bonding between separate polymer chains results in better physical properties (Tough coating) and thermal behaviour (Higher Modulus at high temperatures - Better flexibility).
Furthermore, the moisture sensitivity of polyurethane/hybrids limits the environmental conditions for application. Polyurea can be used in more extreme conditions. 
The graph below demonstrates Polyurea's performance in extreme conditions compared to a typical PU. So, in low temperature and high humidity environments, which are typical conditions inside a water tank, Polyurea is undoubtedly the preferred option. 


Technology Comparison
Polyurea Polyurethane/Hybrids
Fast cure combined with moisture Insensitivity. Fast Cure is possible with a catalyst but is moisture-sensitive.
Due to the high reactivity rate, low activation energy is needed, resulting in a broader application range (Temp / Relative humidity). A lower reactivity rate results in the need for a catalyst and a limited application range.
Excellent Physical Properties A wide range of physical properties are possible.
Limited formulation range due to a limited range of useable amine functional products. A broad range of polyols and chain extenders are available.
Moderate system Cost Lower System Cost
Very fast back to service time of this area Depending on the system but slower back-into-service times

From an equipment standpoint, many applicators seem to be having issues with using the XP70 (Plural 2:1) without quick build-up through the equipment and often end up losing hoses (due to the sensitivity of the catalyst in the A-side). Polyurea is sprayed through reactors and impingement mixing, which helps keep the reaction clean from any reaction inside of the unit as both parts stay clear of one another all the way through the system. The reaction happens at the tip of the gun through the mixing chamber. So our Graco workshop gets a lot fewer reactor issues than other plural equipment (Mainly XP70) used with slow-set Hybrids or Polyurethanes.

Conclusion - After years spent in the development and testing of Polyurea and polyurethane coatings, we recommend the use of Pure Polyurea when it comes to any application that will be in contact with water, especially in immersion (Water facilities). We also highly recommend Pure Polyurea over Hybrids for waterproofing applications to avoid premature failures, especially externally on concrete and steel roofs.

If you have any other issues, please feel free to contact our technical office at 1300 123 085 and speak to either Bryant or Ben.

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