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CMU Block Walls

Mountain Grout Strong

Polyurethane Resins For CMU Wall Waterproofing

CMU (block) walls present a unique challenge compared to poured concrete walls.  They often experience seeping leaks in small voids between the mortar and the block, but exhibit no obvious cracks. Additionally, waterproofing membranes installed at construction fail due to mechanical damage during backfill or due simply to age.

Finally, the blocks are most often hollow, making it even more difficult to inject resin into the specific void area without accidentally filling the void in the block and potentially causing damage to the CMU wall. Therefore, the most common application method using polyurethane resin is to create a waterproof membrane along the back side of the wall to stop leaks before moisture reaches the CMU wall.

The biggest advantage to the curtain grouting method is that no expensive excavation is necessary on the positive side of the wall.  Grout Curtains can be installed behind the wall whether or not a waterproofing membrane was installed during initial construction.  Installers can drill through the mortar joint from the negative side and pump grout with low pressure through packers into the voids and soil on the positive side.  The polyurethane resin reacts with the moisture present in the soil and void to react and form an impermeable barrier, keeping the water where it belongs and the subgrade wall dry. 

It is important to remember that polyurethane doesn’t make water go away. Grout curtains merely stop waterfrom infiltrating voids in walls. Installers (and owners) should be prepared for the groundwater to build head pressure and find a new void if one exists. Therefore, a large grid pattern covering the greater area around a wet spot on the wall is recommended to avoid “chasing” the water for several installations.

If a grout curtain is properly installed, it should mean the end for damp walls, mold, and other common problems associated with subgrade CMU walls.  Call Mountain Grout with any questions.


  • Mountain Grout HL-100
  • Mountain Grout SLV
  • Mountain Grout Flexible
  • Mountain Grout Flex Classic
  • Mountain Grout Ultra
  • Mountain Grout Gel Foam I

(Call a Mountain Grout Rep for recommendation)


  • Mountain Grout Resin of Choice
  • Mountain Grout Pump Flush
  • Injection Pump
  • High Pressure Injection Gun with extra couplers
  • Hammer Drill
  • Drill Bit to match diameter of Packers (3/8”, 1/2”, 5/8”)
  • Socket Set (Deep well, thin wall sockets)
  • Packers
  • Clean 5–gallon buckets
  • Paddle Mixer
  • Personal Protective Equipment (PPE)
  • Plastic Sheeting
  • Tape
  • Assorted Hand Tools
  • Mountain Grout Ureclean Wipes or Rags

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Green Mountain Grout International LLC, Member of the ICRI & Member of the ASDSO.