Prime Practices Manhole

Prime Practices

Sealing Leaks in Brick Manholes with Hydro Gel SX

Call: 1-800-321-7212

Scope of Work: Sealing deteriorated mortar joints and defects in brick manholes by injecting Prime Flex Hydro Gel SX and water using a two-component pump (the M2).


Problem: Deteriorated mortar joints and defects around pipe penetrations allows ground water and soil to infiltrate manholes causing unnecessary treatment, wear and tear on equipment, and cave-ins around the structure.


Solution: Leaks can be sealed and surrounding soil stabilized with injection of Hydro Gel SX, preventing the need for excavation and replacement.


Hydro Gel SX is a hydrophilic, single-component polyurethane resin typically injected with water using a two-component pump that is either fixed ratio (8:1) or variable ratio. This method is called twin streaming. Hydro Gel SX can also be injected as a single component that reacts with groundwater already present. However, experience indicates that less material is used if mixed with water just prior to injection. “Twin streaming” with a two-component pump also generates a better quality gel. A two-component pump that mixes the product just before it enters the wall is needed since it only has a 45-60 second pot life.

Gel Reinforcing Agent can also be added to the water side of the mix. This is a latex additive that increases the strength and flexibility of the Hydro Gel SX. It also helps to reduce shrinkage during dry cycles. Add the Gel Reinforcing Agent at a ratio of 6 to 8 parts water to 1 part Gel Reinforcing Agent. Then use this solution to mix with Hydro Gel SX at 8 parts prepared solution to 1 part Hydro Gel SX using a two-component pump.

Hydro Gel SX can also be used with oakum to seal larger defects or to form a custom fit flexible seal around pipe penetrations. (See Activated Oakum Technique.)




Injecting a hydrophilic, water-activated polyurethane resin into the outside of the manhole will allow the material to migrate and soak into and against the leaking mortar joints and around pipe penetrations, creating an impenetrable gel or foam curtain while also stabilizing the loose soils surrounding the manhole.



Start with the leaking areas and after sealing, check for infiltration that has migrated to other areas.



  • Drill 3/8” to 5/8” injection holes through the manhole at 120-degree angles from each other at (10 o’clock, 2 o’clock and 6 o’clock) on the same plane of elevation. Rows should be separated no more than three vertical feet, and the holes should be staggered with the holes in the rows above and below. Provide additional injection holes near observed defects and at pipe seals.
  • Inject grout through the holes under pressure with a suitable probe. Injection pressure should not cause damage to the manhole structure or surrounding surface features. Grout should be injected through the lowest holes first.
  • Repeat the procedure until the manhole is externally sealed with grout.
  • Injecting through the manhole wall to the exterior will allow the Prime Flex Hydro Gel SX to migrate and be pulled back into the defects by the hydrostatic flow of the leaks. The Hydro Gel SX will flash set to form an impenetrable foam / gel curtain sealing off all leaks and stabilizing soils on the external side of the manhole.
  • The injection holes can be plugged with oakum until resin has set. Holes then can be sealed with epoxy gel or Prime Plug 1, 2 or 3. (See Activated Oakum Technique.)


Safety Considerations:

  • Carefully read MSDS/SDS prior to handling any chemical.
  • Always wear safety goggles when drilling, grinding, flushing, injecting or handling resins.
  • Always wear protective clothing, chemical resistant gloves and safety goggles at all times when handling resins. Blowouts can occur when injecting resins at high pressure.
  • Be aware of potential electrocution hazards when working with power equipment in wet environments. Keep water away from electrical cords and electrical equipment.
  • Make sure no loose clothing can come into contact with moving mechanical equipment.
  • Follow all OSHA confined space entry requirements where applicable.
  • Keep first aid kit (eye wash, bandages, etc.) present on site with easy access.


Materials List (Items listed below in bold are available from Prime Resins):

  1. Prime Flex Hydro Gel SX
  2. Gel Reinforcing Agent
  3. Brass F- Valve
  4. Stainless wall stinger nozzle
  5. Oil-free/dry oakum
  6. Prime Plug 1, 2 or 3
  7. Prime Flex Eco Flush
  8. Empty 5 gallon pails


Equipment List:

Rotary hammer drill
1/2” drill bits for stainless wall stinger nozzle
Two-component low pressure pump (M2 Pump system)
Flathead screwdriver (for applying oakum)
Hammer (for seating wall stinger)
Safety goggles
Chemical resistant gloves
Tyvec suit


Activated Oakum Technique