Curing CIPP Liners at too High a Pressure

“I cure my liners at 20psi but one of your sales trainers told me I’m curing it at too high a pressure. I don’t think I have a problem and my liners look good after I’m finished. If I don’t cure at that pressure won’t my liner shrink and not adhere to the pipe wall?”

Let’s start with your last statement. CIPP liners regardless of the resin used, do not adhere to the pipe wall. CIPP liners provide a very close fit to the host pipe but there is no binding of pipe molecules with resin molecules that you would find in adhering conditions where you actually have a molecular exchange between materials. No material how high the pressure you will always have a space between the host pipe and the liner although it may be small. But that’s not where the problems start cropping up.

The bigger issue with high-pressure curing is the resin migration out of the lining material and into the cracks, pipe defects and up to any tie-ins you’ve lined over. Think of this way. If I soak a cloth in water and lift it out of the bucket I wetted it the cloth will be full of water or saturated. If I wring out the cloth the water migrates out and runs away. The same effect occurs when curing at high pressure – you squeeze the resin out and it runs away to areas that may not provide any help in repairing the pipe defect you’re trying to fix. If you are using a lining material that features a stitched seam, you also run the risk of pressing the stitching so tightly it penetrates the coating used for the wet-out process.

While in most cases this may not be apparent for years but if you’ve penetrated the stitching during the curing operation at too high a level, you may see the resin ooze out and away from the cured lining material leaving pinholes where the stitches passed through the material to seam it. These pinholes will leak and as soon as roots find the leak in the material they will send small microscopic roots through the holes. Years later a root intrusion occurs and you will have a claim that will require you to fix it.

The final insult to over-pressuring is resin running up into tie-ins. If you’ve never tried removing 2” or 3” or more of hardened resin plugging a tie-in you’ll do anything you can to avoid it. Removing resin slugs cost time and money and your customer won’t pay you more money to remove the slugs.

We recommend curing between 5 psi and 10 psi. This pressure range produces minimal resin migration and still cures the liner. We suggest this protocol for the cure. Once the CIPP liner and calibration tube are in place you should run the pressure of the liner/calibration tube combination up to 25 psi to 30 psi and hold it for 25 to 30 seconds. This stretches the material to its’ full potential and when pressure is relaxed to 5 psi to 10 psi it will remain in the stretched position. It will minimize any resin run up from entering the tie-ins. If you’d prefer no resin run up into tie-ins, using a pre-liner will prevent any excess resin run-up.

For more information, call us at +1-888-354-6464 or write to us at

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