Polyurethane foam also fills the crack or joint with a resin that
expands in the presence of moisture. Unlike epoxy, polyurethane
foam is flexible enough to accommodate movement in the crack or
joint due to changing soil pressures or minor settlement.
Since polyurethane resin systems expand during the injection, less
resin is required to accomplish the repair and can be much more
economical to install especially in wide cracks and loose soil
conditions.
Wet or actively leaking cracks and joints often will have better
results being injected with polyurethane foam. In fact, because
polyurethane resin systems are moisture reactive, they may
actually require the crack to be pre-wet with a small amount of
water in order to activate the full expansion of the resin
There are epoxies that will work well in wet conditions as the
epoxy will displace the water during the injection process, but
extra care needs to be taken to "flush out" any resin that combines
with the water. (More on how this is accomplished later.)
For very wide cracks or joints, the polyurethane expanding foam
systems will fill the crack and do so with a fraction of the resin that
would be required if epoxy was used. When encountering unusual
repairs such as cold joint type leaks or honeycombing, expanding
polyurethane grouts are the material of choice to be able to attack
the hidden unknown of these types of repairs.
Deep subterranean concrete repair in tunnels and municipal
systems often involve actively leaking cracks and joints that will
require specialized fast-reacting polyurethane grouts that can be
employed as "cut-off' grouts to stop high-pressure, high-volume
water flow. Most of these polyurethane g
are mixed with an
optional catalyst that allows the reaction time to be adjusted to
react more quickly if needed to meet the jobsite conditions which
can vary job to job