Annulus Space & CIPP lining

“Why are my liners pulling away from the wall of the host pipe? I know you’ve said that the liner can be designed to be stand alone and I’m not worried that it’s strong enough to stand up, but what about tie-ins and water tracking? Will the roots we’ve tried to eliminate find a path back in if it follows the space between the host pipe and the liner and comes out at the tie-in? I use a polyester resin and one of your competitors liner material. I’m worried about the roots collapsing the liner or plugging the line I just lined. Suggestions?”

There are a couple of things going on here. First of all let’s talk about liner sizing and a possible contributor to the problem. We, as suppliers set a “cut size” for every liner we produce. These “cut sizes” vary depending on a few variables. For liner that is installed using a pull in place method, the liner “cut size” is very close to the actual interior diameter of the pipe. We produce a couple of sizes in this category depending on whether the pipe is cast iron or other types of pipe. Cast iron pipe is cut to a smaller nominal size than the advertised pipe size. 4” cast iron pipe is actually 3.94” inside or 98.5% of a full 4” pipe. When we deduct a 3mm tube thickness we take the finished inside diameter to 3.704”. If the pipe isn’t cleaned down to the original diameter and we produce a liner that finishes 4” after the liner is installed, it will wrinkle. We then produce liner that accounts for this smaller diameter and make an allowance for the material to stretch to the wall of the pipe and not wrinkle. Each manufacturer produces liners to fit the pipe. If your producer is providing you with liner cut for cast iron but installed into clay, ABS or PVC, it may not stretch to the pipe wall and leave the gap or annulus.

Annulus Space

The second contributor is the polyester resin. The ester family of resins including polyester and vinyl ester both tend to shrink during the curing process. If using these resins you will notice a shrinkage of the pipe after curing Epoxy resin also shrinks but usually not as much as the esters, however, some producers add fillers to the resin that may contribute to extra shrinkage. If you are not sure if your provider is giving you a filled resin, a tell-tale indicator is whether or not you need to pre-mix either the base or hardener of epoxy before mixing the components. It’s not necessarily a bad thing to add fillers but it’s good to know if they have been added, for what purpose, and whether the component will add to the shrinkage issue.

There are after market products to add to liners that swell up in the presence of water. Some producers sell liners with hydrophilic seals while some contractors purchase bulk seal material and add them into the liners in the field. These are typically used at the front end and the other end of the liners however usually aren’t available for tie-ins opened after the lining process is complete.

As far as collapsing the liners? Most likely not provided the resin/tube thickness meets the design thickness called for on the job you are doing. This doesn’t mean you can get roots to invade the annulus left when cutting open a tie in that allows water to track between the host pipe and the liner.

For more information contact us at 888-354-6464 or write to for a full listing of materials and supplies that can help you solve your problem.

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