Coating Cast Concrete using EPDM Liquid Rubber
Only true EPDM in Liquid form in the World
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Coating Cast Concrete using EPDM Liquid Rubber

Why do I need to use a primer on cast concrete?

Cast concrete has a more porous surface than concrete that has been trowel finished. This is because ‘bugholes’ (surface voids) form as a result of entrapped air coming to the surface during consolidation, resulting in a pitted surface finish. Whilst bugholes are primarily an aesthetic problem for exposed structural concrete, problems do arise when the surface is to be coated.

If Liquid Rubber is applied directly to a cast concrete surface, then a large number of pinholes or craters will form in the cured membrane, where the liquid has filled the voids on the substrate. In order to avoid the formation of these surface craters in the membrane, it is recommended to seal the concrete. This will also strengthen and reconstitute a leached or spalling surface. 


Choosing a primer

The choice of your primer will be directed by temperature and relative humidity.

IF the:

  • temperature is 15.6°C (60°F) or higher
  • relative humidity is 70% or lower 

Use a water based Acrylic Elastomeric coating (primer or base-coat version) 

IF the:

  • temperature is 15.6°C (60°F) or lower
  • relative humidity is 70% or higher 

Use a solvent based Neoprene Rubber, Chlorinated Rubber or Hypalon product


Priming your cast concrete surface

  • Based on the conditions above, choose your primer and apply a light coat to seal the surface.
  • If using a water based coating, allow this to dry thoroughly, as any remaining moisture will negatively impact on the adhesion of the Liquid Rubber layer. 
  • Apply the Liquid Rubber when the base coat is sufficiently dry, but within 3 days, remembering that a single application of Liquid Rubber is preferable to multiple coats.