Expanding or Permeating Polyurethane Resin, what’s the big deal?

Expanding or Permeating Polyurethane Resin, what’s the big deal?
Polyurethane Resin Types Defined

By J.R. Crowell
June 18, 2020

Polyurethane resins are not created equal.  There are several different types, each with their own intended projects.  Some projects have an overlap and some projects have their greatest success with one or the other, not either or.  Read along for a brief discussion on the differences.

Expanding Polyurethane Resins:

As the name suggests, expanding resins start off as a liquid and end up as an expanded solid.  These resins are plural component (primarily 2 parts) that mix together creating a chemical reaction that causes expansion.  Expansion takes place as fast as 15 seconds and are ready for regular traffic in as little as 30 minutes (compressive strengths up to 14,000 lbs per sq ft in a free rise state). 98% of the time we are referring to a hydrophobic chemical meaning it is water impermeable and essentially displaces moisture. As these resins expand throughout a treatment area they fill voids and compact soil.  The strength of the soil in treatment areas comes from the compaction and compression from the expanding resin against the soil.  Expanding resins are used primarily for:

  • Lifting settled concrete.
  • Filling voids.
  • Stabilizing soil where permeation is minimal.
  • Supporting and lifting structures.

Permeating Polyurethane Resins:

Any guesses on what this material does? If you guessed “permeate through the soil”, you guessed right.  Unlike its brother, expanding resin, permeating resin actually encapsulates and combines with the soil instead of displacing it.  The low viscosity resin permeates through the soil (just like water does) and encapsulates soil properties to create a solid, rock hard, impermeable mass (compressive strengths around 2,085 psi!). This resin is also referred to as a “single component” resin.  This is because the cure time is manipulated by adding more or less catalyst to the reactive mixture.  This manipulated set time becomes extremely important when working on leak seal and soil stabilization projects where premature cure times could result in a subpar repair.   Permeation resins are primarily used for:

  • Infiltration/inflow repair.
  • Soil stabilization.
  • Negative or positive side side sub grade leak seal.
  • Pre-construction stabilization.

That’s the quick and dirty on expanding and permeating resins.  If you’ve followed us for any length of time, you know we are adamant about education on the differences of these resins and the repairs where they excel.  Make sure you know which resins are being spec’d for your project to guarantee you are getting the most bang for your buck.

Check out our services page for more information on projects where these different resins are used.

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