Curing the Liner

Best Practices – 10th in the Series

Ambient & Heat Cure

When it’s time to cure the CIPP liner we have 3 methods that are proven and tested and a 4th one that is emerging. We will explore the ambient and heat cure methods. With any of these systems, we want to stretch the liner to fill in voids, smooth out wrinkles in any turns and bends, and expand to fit tightly to the host pipe.

  1. After the inversion of the calibration tube, while the calibration tube is still connected to the inversion unit, slowly increase the air pressure up to 30 psi.
  2. Hold the pressure for 30 seconds which allows the fabric-soaked resin to stretch out filling voids, smoothing wrinkles and expanding the fit tightly to the host pipe.
  3. Reduce pressure, disconnect from the Quik-Shot ™ or inversion device and connect to the heat or air curing manifold.

We’ve formulated our resin formulations for curing at ambient temperatures however heat can speed up the process to a point. If we allow the addition of heat to drive the temperatures above 210F, we can cause the formation of the resin chains to form too quickly and form stress cracks. The ground temperature is partially controlling our exotherm by cooling the resin and not letting the temperature to rise above the 210F temperature.

Ambient Cure: Using the ambient temperatures to allow the resin chains to form through the exothermic process. We’ve formulated the chemistry in all three approved resin systems to cure under these conditions. A couple of considerations for using any of the resin systems that fall into this category. All resin systems may be formulated to cure overtime at ambient temperature but heat accelerates the curing of these resin systems.

Portable Compressor
  1. After stretching the tube while still connected to the inversion gun, the pressure is dropped to zero and the tube is removed from the inversion unit.
  2. An air manifold is attached to the calibration tube, again using two hose clamps torqued to 60-inch pounds.
  3. A small compressor may be used for this purpose as the amount of air needed is to inflate and hold pressure as opposed to processing a volume of air
  4. Slowly inflate the calibration tube to a level of 5 psi to 8 psi and hold
    • This pressure will push the tube out to the level it was stretched to when held to 30 psi for the 30 seconds mentioned above
    • Overpressuring the tube at this point will drive resin out of the tube and away from the liner into defects in the pipe. If any tie-ins that have no pre-liner covering the opening will drive a resin slug up the tie-in and be very difficult to remove.
  5. Follow the resin suppliers timelines for various temperatures for curing
  6. When you reach the prescribed curing time schedule, deflate the calibration tube but do not remove it
  7. Insert your camera down the line between the calibration tube and the liner to see if you have cured the tube to the point it will stand on its own.
  8. If you observe and soft areas, re-inflate the tube and continue waiting, checking hourly until cured.
    • Soils temperatures may vary throughout the length of the lined pipe
    • Groundwater moving through the ground may be affecting the temperatures inside the pipe
  9. Upon finishing the curing process, you can disconnect the tube from the manifold and reconnect the line to the rest of the plumbing
    • Salvage and label the length of the calibration tube for future use as a pre-liner
    • A best practice here is to install a clean-out at the installation point for future maintenance
    • As you connect the old plumbing to the newly lined pipe you will most likely use Fernco style connectors. A good practice here is to bury root control chemicals near the connectors to prevent roots from trying to penetrate the Fernco connectors in the future.
  10. Backfill or restore the area and clean-up the site for departure

Heat Curing: Hot Water and or Steam Curing can accelerate an ambient cure resin system. Hot water is pretty straight forward in that your only monitoring is to watch the pressure during the curing process adding make-up water to cover any leakage in the calibration tube while steam curing requires the operator to monitor the temperature inside the tube to make sure the steam temperatures remain below the 210F temperature by cutting steam and adding air when needed to control the exotherm.

  1. Hot Water Curing
    1. Remove the calibration tube from the inversion gun.
    2. Connect the recirculation hose to the manifold making sure that you have not twisted the hose to ensure circulation
    3. Connect the calibration tube to the manifold
    4. Connect the red supply hose to the manifold and to the supply side from the heater
    5. Connect the black return hose to the manifold but do not connect the return hose to the heater
    6. Connect the supply water hose to the fill port on the heater
    7. Start the water flow and fill until the return water exits the open black hose without air bubbles
    8. Stop the water flow fill valve and connect the return hose to the return port
    9. Set the Temperature desired     
      • 180F recommended
      • If the supply water is extremely cold as found in northern climates, the boiler may be started during the filling process to raise the water temperature
    10. Monitor the pressure and hold pressure between 5 psi and 8 psi.
    11. We expect the return water to be at or above 125F return and time for 1 hour
      • If there is groundwater present, the time may take longer to cure and there’s no effective way to measure the amount of groundwater nor temperature
      • If the boiler cycles within the first 10 minutes of curing and shows a high return temperature, disconnect the return waterside and measure flow by filling a pail of water. If less than 5 GPM, check flow rates of your system for kinks in hoses
    12. Upon completion of curing you have two methods of handling the water in the calibration tube 
      • Remove the calibration tube from the manifold
      • Using a razor blade attached to the camera insert the camera to the far end and cut the end of the calibration tube allowing water to drain into the downstream line.
      • Using a tub, sump pump and hose, pull the water back into the tube and pump out of the area to an outdoor disposal area.
    13. Salvage
      • Salvage the calibration tube and mark the length for future use as a pre-liner
      • Salvage the recirculation hose and mark length for future use
    14. Clean up the area and return the sewer to service by reconnecting to the existing sewer line.

For more information regarding this post contact Pipe Lining Supply at 1+-888-354-6464 or write to

Tags: , , , , , , , , ,