PennCoat, Inc. compliments Epoxy Coatings with Aliphatic Urethane top coats.

Aliphatic Urethanes


Aliphatic urethanes are a top coating that provides an additionally layer of protection to epoxy floor systems and industrial paint coating systems.  It is tough and flexible, adding strength, abrasion resistance and protection.  Because of its resistance to UV, chemicals, and water, aliphatic urethanes are a popular choice for outdoor surfaces that are weathered or exposed to the deteriorating effects of UV sun light.

Breakdown of Aliphatic Urethanes:

  • Performance properties
  • Outdoor Usage
  • Application

Performance Properties

Often, epoxy finishes are created to help maintain and preserve the medium which they are applied to.  Although durable, epoxy finishes, especially if decorative, can be vulnerable to difficult conditions.  Excess water can promote osmotic blistering, sun light can deteriorate and fade epoxy, and vibrations or oscillations from machinery can break down an epoxy application.  So coating specialists will apply a final top coat of aliphatic urethane to help preserve the base coat of epoxy.

Aliphatic urethane is an excellent sealant.  Epoxy coatings that are exposed to a lot of chemicals or water can become vulnerable, promoting deterioration.  An aliphatic urethane top coat can improve the strength and longevity of the coating, preventing these deterioration catalysts from contacting the epoxy.

But not only do aliphatic urethanes prevent water or chemicals, it also protects epoxy coatings from UV rays.  UV rays from the sun can weaken the epoxy coating, and also fade the color, leaving an unpleasant yellowish tint.  Often epoxy coatings are preferred for outdoor work, so they would require a coating of aliphatic urethane to protect it from the sunlight.

Additionally, aliphatic urethane has an excellent tensile strength.  Sherwin Williams’ Acrolon Ultra, a favorable top coat that contains aliphatic urethane, offers a tensile strength of 1766 psi.  This is a powerful bond that won’t separate from the epoxy.  Areas that are subject to constant vibrations or oscillating machines can slowly disband most coats.  But aliphatic urethane has excellent flexibility, making it very tolerant to work environment of heavy usage.

Outdoor Usage

Epoxy coatings are often applied to areas that are permanent outdoor fixtures: water tanks, sports complexes, bridges, marines, stadiums, etc.  The epoxy is a reliably solid coat that can offer protection and preservation.  However, it can be vulnerable to weathering, sunlight, and extensive vibrations, which make aliphatic urethane an ideal top coat for epoxy.  Aliphatic urethane is UV resistant, allowing an epoxy coating to be applied outdoors.  Typically, epoxy by itself can be damaged by too much sun light.  But a protective top coating can increase its versatility, allowing it to be applied in more vulnerable areas.  And not only does aliphatic urethane offer protection from UV, but it is also resistant to water and vibrations.  So if an epoxy coating is being applied outdoors, as long as it is given an aliphatic urethane top coat, then it can with stand the constant weathering that these areas endure.


As a top coat that provides a lot of benefits, aliphatic urethane offers a fairly simple application process.  As with any coat, the substrate needs to be thoroughly cleaned.  Remove any dust, oils, dirt, or residue that can interfere with the bond.  One of the best features of aliphatic urethanes is its ability to bond well with epoxies.  So you’ll want to make sure you don’t prevent this benefit by forgoing prep work.

As far as temperature application, aliphatic urethane top coats have a very broad range.  They can be applied between 40 degrees F to 120 degrees F.  Aliphatic Urethane coatings are very thick, with a high viscosity, making them less vulnerable to temperature range.  However, their cure time can be extensive, especially in the cold, taking as long as 14 days.  However, the cure time will decrease as the temperature increases, requiring about 10 days for 80 degrees F, or 7 days for 120 degrees F (although we don’t recommend working in temperatures that high).

In conclusion, after applying an epoxy coat outdoors, it is recommend that the epoxy coat receives a top coat containing aliphatic urethane.  As mentioned above, its ability to improve an epoxy’s performance will allow that epoxy to last longer with outdoor usage.  And the longer the epoxy coat lasts, the longer the substrate it is protecting will last.