Why branch drains are a different lining problem
Drain pipelining in Denver means lining the two, three and four inch branches that collect a kitchen, a bathroom group, a laundry or a floor drain and carry it to the stack or the building drain. A sewer lateral is mostly straight; a branch drain in a house of any age turns a corner every few feet. Code prefers long-sweep fittings on drainage, but what is actually in the wall is often a tight-radius elbow, a sanitary tee where a wye belonged, or two 45s set close together to make an offset. Every one of those has to be passed by a liner that would rather stay straight, and each is a place where the liner can fold, thin out, or stop.
Inversion or pull-in-place through a bend
Small liners go in one of two ways. Inversion turns the resin-saturated tube inside out with air or water pressure from an access point, so the liner rolls itself along the pipe and around each bend with the resin on the outside pressed against the wall. Because the tube is unrolling rather than being dragged, it follows a 90 more willingly and does not scrape resin off against the fitting. Pull-in-place draws a flat liner through on a line, then inflates a bladder inside it to press it against the wall for the cure. It gives more control over where the liner ends and suits short sections between two access points, but a tight elbow can bunch the liner on the inside of the turn. For a branch with several bends, inversion is generally favored; for a straight run between a cleanout and a fitting, pull-in-place wins. Either way the liner is sized slightly under the host diameter so it can stretch around the outside of a bend rather than crumple on the inside.
Controlling wrinkles
- Liner construction. Flexible, stretchable felt or knitted tubes built for bends, not the stiff glass liners used on straight mains; a liner that cannot elongate on the outside of a 90 will wrinkle on the inside.
- Resin quantity. Too much resin pools on the inside of a bend and cures as a lump; too little leaves the outside dry. Wet-out is calculated for the liner length, not eyeballed.
- Inflation pressure. Held at the figure the liner maker specifies for the diameter, high enough to press out folds, not so high that the liner thins on the outside of the bend.
- Cure timing. The liner stays at pressure until fully cured; a bladder released early lets a bend relax and fold.
- Camera afterward. The post-cure video runs every bend in both directions looking for fins and folds.
A crew offering drain pipelining in Denver should be able to name the liner product it uses for bends and the cure pressure, because those two figures are most of the difference between a smooth 90 and a wrinkled one.
Transitions, traps and cleanouts
A branch drain rarely keeps one diameter from end to end. Where a two-inch branch joins a three-inch collector, the installer either uses a stepped liner built with the change in it, or lines the larger pipe first and inverts the smaller liner into it with an overlap of several inches, so the second liner cures onto the first. Overlaps are placed on straight pipe, not in a fitting, and the downstream liner goes in first so the lap faces with the flow. P-traps are not lined through: the trap is removed, the liner is inverted from the trap arm, and the trap is replaced afterward. A cleanout is the preferred launch point on any branch in Denver; where none exists the liner goes in through a pulled fixture. The description at how a small liner is inverted through a bend shows what an inversion looks like as it reaches a fitting.
Every branch and vent the liner passes must be cut back open. A liner inverted along a horizontal collector seals over the tee where the vent rises and the wye where the next fixture joins. A vent sealed shut siphons traps and lets sewer gas into the room; a sealed fixture branch simply stops draining. Insist that the proposal lists every connection to be reinstated and that the post video shows each one open.
Reinstating vents and branches on small pipe
On a four-inch lateral the branches are reopened with a robotic cutter that drives to the footage. In two and three inch pipe the cutters are smaller, pushed on a rod, and slower, and reaching a connection just past a bend is often not possible. Installers plan for that by ending a liner short of a fitting the cutter cannot reach, launching a second liner from the far side, or opening the connection from the fixture end after the cure. Vents deserve particular care, since a partially reopened vent may look fine on camera and only show itself as a gurgling trap months later. The reinstatement list in the proposal should include the vents, not just the drains.
When a bend is too tight to line
Some fittings should not be lined. A short-radius 90 in two-inch pipe, two 90s within a foot of each other, a sanitary tee taken from the branch side, or a bend that the camera shows is already crushed or offset will fold any liner pushed through it, and the fold becomes a permanent catch point that clogs more reliably than the original pipe. The honest answer at that fitting is a short open cut to replace it, a new cleanout there so the runs on either side can be lined separately, or leaving that section alone if it is sound. Any of the verified CIPP installers serving Denver who take on branch work in Denver should carry the small-diameter liners and cutters this work needs, and the ones worth hiring will point to the bend on the video they are not going to line and say why.
Common questions in Denver
Can drain pipelining in Denver go around a 90-degree bend?
Usually, with a flexible liner built for bends, correct resin quantity, and inflation held at the maker's specified pressure through the full cure. Inversion follows corners better than pull-in-place. A short-radius 90 in small pipe, or two 90s close together, may still be too tight and is better replaced.
What causes wrinkles in a lined branch drain?
A stiff liner that cannot stretch on the outside of the bend, too much resin pooling on the inside, inflation pressure below the maker's figure, or a bladder released before the cure is complete. Each shows on the post video as a fin or fold at the bend.
How is a diameter change handled?
With a stepped liner made for the change, or by lining the larger pipe first and inverting the smaller liner into it with an overlap on straight pipe. The downstream liner goes in first so the lap faces with the flow and does not catch debris.
Is the P-trap lined too?
No. The trap is removed, the liner is inverted from the trap arm, and the trap is reinstalled after the cure. Lining through a trap would leave a tight double bend with no way to reach it with a cutter and no way to clean it later.
What happens to the vent connections the liner covers?
Each one is cut back open from inside with a small cutter or opened from the fixture end after the cure, then shown on video. A vent left sealed siphons traps and lets sewer gas into the building, so the reinstatement list should name every vent, not only the drains.