Mapping the under-slab system first
Trenchless cast iron sewer pipe repair in Denver begins with a map, because the pipe under a slab is not one line but a tree. Fixture branches from tubs, showers, toilets and sinks feed a building drain that runs under the floor to the footing, and none of it can be seen. The crew films from every reachable opening and pushes a sonde with the camera so each run can be located and marked on the floor. The result is a sketch with footages, branch positions, the exit point and, critically, which opening gives the straightest path into each run. That sketch governs which segments get lined, from where, in what order, and how long each fixture is out of service.
What the camera typically shows in old cast iron
- Bottom-of-pipe roughness. The flow line is pitted and channeled while the upper wall looks intact, so the camera appears to be riding in a rough trough.
- Scale ledges. Rings of hard deposit narrow the bore at intervals and catch the camera head, often mistaken for offsets.
- Weeping joints. Dark staining or a thin water line at each hub where the lead has loosened.
- A dip near the exit. The building drain often sags where it passes from compacted fill under the slab to the trench outside, and standing water on video marks the spot.
- A change of material. Somewhere just beyond the footing the picture changes to clay or PVC, and the footage where that happens is recorded.
The survey also notes whether each segment can be cleaned to a lineable wall or has already lost its bottom, since that decides spot repair against full liner early.
Choosing the access points
The whole trenchless case rests on getting a liner into a pipe that has no exposed end. The options, roughly in order of preference, are an existing cleanout, a toilet flange with the fixture lifted, a tub or shower drain with the trap arm disconnected, a roof vent for a vertical run, and finally a new cleanout cut in through a small opening in the floor or outside the foundation. A lining crew in Denver will usually try to run the main building drain from an exterior cleanout back toward the house and the fixture branches from their own openings, so that no branch has to be lined through a tee. Where the house has no exterior cleanout, installing one just outside the foundation is often the first task, and that one small excavation becomes the launch point for the building drain and the tie-in to the lateral. For trenchless cast iron sewer repair in Denver, the proposal should list every access point by fixture or location, because that list is what the crew will actually use.
Cleaning to a lineable wall
Under a slab the descaling step is limited by the same openings. A flexible shaft descaler is fed through a toilet flange or cleanout in short passes, followed by a camera to confirm that the scale is off and the wall is still there. Debris is flushed toward the exterior cleanout for recovery rather than pushed into the lateral. Small branch lines are cleaned with smaller heads, and the crew is careful at every hub, because a shaft tool that catches on a joint step can wander into the wall. This stage is where the plan gets revised: a segment expected to take a liner may prove too thin, and one written off may clean up well.
Line the branches before the main, not after. A branch liner terminating into an unlined building drain can be trimmed flush at the tee; a branch liner installed after the main is lined has to be cut through the new main liner and sealed at the junction. Crews sequence the small lines first so every junction is made once.
Spot repair versus full liner under the slab
A single failed joint or a short section of channeled invert on an otherwise sound run can be covered with a sectional liner placed from the nearest opening, cured on a packer and left as a short sleeve. That is the right answer when the defect is isolated. Once the camera shows two or three problem areas on one run, or the invert is channeled end to end, a full-length liner from opening to exit costs little more than the sections and leaves no seams. Pull-in suits under-slab work in Denver because the liner is drawn between two openings, a toilet flange and the exterior cleanout for example, and inflated with a calibration hose rather than inverted through a fixture. A description of how under-slab drains are accessed and lined shows the pull-in setup between openings and how the liner is trimmed at each end.
Through the foundation wall and into the lateral
The building drain leaves the house through or under the footing and, within a few feet, becomes the lateral in a different material. Lining through that transition takes care. The liner is sized for the cast iron bore and can pass into slightly larger clay or PVC, but a step down, a reducer or a badly offset joint at the material change will stop or wrinkle it. The exterior cleanout is placed at or just past the transition so the cast iron liner terminates there cleanly and the lateral can be inspected and, if needed, lined as its own segment. Where the pipe passes through a foundation wall rather than under it, the sleeve or the wall may pinch the pipe, and the crew films that spot before committing a liner. A collapsed section at the footing is the one place under-slab work in Denver sometimes needs a small exterior dig, made from outside so the floor stays whole. Installers among the verified CIPP installers serving Denver document the transition footage and the termination point on the final video, which the next owner's inspector will want to see.
Common questions in Denver
How does trenchless cast iron sewer pipe repair in Denver get into a pipe under a slab?
Through openings the house already has: cleanouts, toilet flanges with the fixture lifted, tub and shower drains, and roof vents for vertical runs. Where no exterior cleanout exists, one is installed just outside the foundation and becomes the launch point for the building drain.
Are the branch lines or the main drain lined first?
The branches. A branch liner finished into an unlined main can be trimmed flush at the tee, whereas a branch lined afterward must be cut through the new main liner and resealed. Sequencing the small lines first means every junction is made only once.
When is a spot repair enough under a slab?
When the camera shows one isolated defect on a run that otherwise cleans to sound wall. A sectional liner is placed from the nearest opening and cured on a packer. Two or more defects, or an invert channeled end to end, tip the decision toward a full liner from opening to exit.
What happens where the cast iron changes to clay or PVC outside?
The liner can pass into a slightly larger pipe but not through a step down, a reducer or a badly offset joint, so the exterior cleanout is set at or past the transition. The cast iron liner ends there and the lateral is handled as its own segment in its own material.
Does the floor ever have to be opened?
Rarely. A collapsed section right at the footing or a run with no usable fixture opening may need one small access hole, and where possible it is made outside the foundation rather than through the slab. Everything else is done from existing openings.