Preventing Roots From Growing Through a CIPP Liner

The author provides some valuable lessons about the wet-out process learned from a failed lining job

Preventing Roots From Growing Through a CIPP Liner

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Have you ever experienced a root growing through a CIPP liner? I have, and while it’s considered a failure, it is also a great teaching moment.

So how did it happen? My wet-out and installation crew was fully seasoned. They’d installed over 1 million feet of CIPP liner, yet there was a root growing through an 8-inch lined pipe, clearly visible in the CCTV inspection images. I got called out because of the root intrusion in our supposedly “root proof” liner. My job was to figure out why and, more importantly, what I was going to do about it.

After getting all the necessary permits to open up the street, our first job was to come up with a fix before we started on the remedy. We agreed on a point repair of the liner, but the agency wanted to see why the problem occurred in the first place, hence our digging out the failed section of liner and analyzing it.

Our bury depth at this location was only 8 feet, so we used a smaller excavator that got us down to the pipe. We had to include shoring to prevent a cave-in, and then sent a crew in to cut out a 4-foot section of pipe. 

Once we got it to the surface to analyze, the cause was easy to determine. There was no resin in the area on the tube where the root pushed its way through. These were the days before we added pigment to the resin to more easily identify full saturation. Our resin color was similar to the color of the tube, and the crew obviously missed a dry spot in the tube during wet-out. As the tube offers no structural strength to the completed composite, the absence of resin in a dry spot would be easy for roots to penetrate.

There are a couple of lessons to take away from this experience. The first is to make it easy to identify wetted-out tube from dry tube. The addition of pigment takes care of this issue. During wet-out, it’s much easier to see a dry spot than it is when the tube and resin are close to the same color.

The second lesson is that we need to regulate the speed of the tube passing through the pinch roller. We have to allow the vacuum pump time to withdraw the air in the liner tube. If we let the liner move through the pinch roller with an air pocket left in the tube, that pocket may never fill in with resin. We need to ensure we don’t overrun what the vacuum pump can extract. Nor can we allow the resin slug holding a vacuum break breach the vacuum. In other words, let air in past the resin slug by dropping the slug so air can pass through the liner.

Hopefully the lessons we learned the hard way can keep you from repeating the same mistake.


About the Author: John Heisler is the owner of Pipe Lining Supply and Quik-Lining Systems. He has more than 20 years of experience in the CIPP lining industry and over 40 years in the underground construction industry.



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