CIPP GAPPING (STOP-AND-START) IS SAFE, EFFECTIVE, AND LEGAL WHEN DONE TO ASTM F1743

If you’ve heard someone argue that “gapping” is inherently unsafe or “not allowed,” you’re usually hearing a word problem, not an engineering problem. In the field, “gapping” is commonly used to describe stop-and-start sequencing: lining in phases, lining reach-by-reach, and working around operational constraints (occupied buildings, limited shutdown windows, access limitations, bypass pumping needs).

The real issue is not what you call it. The issue is whether the finished liner quality meets the governing installation practice. For pulled-in-place cured-in-place pipe (CIPP), the central practice is ASTM F1743, which describes installation of a resin-impregnated fabric tube pulled into an existing conduit and inflated via a calibration hose before curing.

WHAT ASTM F1743 ACTUALLY REQUIRES: “CONTINUOUS” AS A QUALITY OUTCOME

ASTM F1743 uses “continuous” in two related ways.

First, it describes the cured result as “continuous and tight fitting.”

Second—and this is the part that matters for the “continuous means what?” debate—ASTM F1743’s workmanship language treats “continuous” as a workmanship/acceptance condition: the finished CIPP should be continuous over the entire length of an installation and free of dry spots, lifts, and delaminations.

ASTM F1743 also defines the defect terms so everyone is talking about the same thing. A “dry spot” is an area deficient or devoid of resin, “delamination” is separation of layers, and a “lift” is a portion of CIPP departing from the host wall creating reverse curvature.

In other words: “continuous” is not a slogan. It’s tied to finished-liner integrity and the absence of recognized defect conditions.

WHAT “GAPPING / STOP-AND-START” MEANS IN PRACTICE

In real projects, stop-and-start usually means one or more of the following:

Sequenced installations. The contractor lines one reach during a controlled shutdown window, restores service, then lines the next reach in a later window.
Reach-by-reach work between access points. The project is broken into manageable segments based on cleanouts, manholes, bends, or building access constraints.
Operational constraints management. Bypass pumping, temporary flow control, and occupant communications are used to line without creating backups or extended downtime.

None of that conflicts with ASTM F1743. It’s simply project sequencing. The controlling question remains whether each installed CIPP section meets ASTM F1743 workmanship: continuous over the installation length and free from dry spots, lifts, and delaminations.

WHY STOP-AND-START CIPP IS SAFE

Safety with CIPP comes from control: trained crews, correct equipment, correct resin handling, correct cure protocols, and verification. ASTM F1743 explicitly recognizes that atmospheric hazards may exist in access structures and directs users to evaluate for toxic/flammable vapors or oxygen deficiency before entry, consistent with applicable safety requirements.

Stop-and-start sequencing can improve safety because it reduces “all at once” pressure. Crews can isolate one reach, control the work area, manage bypassing and access, complete curing, verify results, and then move to the next reach with documented lessons learned.

WHY STOP-AND-START CIPP IS EFFECTIVE

Effectiveness means the rehabilitation performs in the ways owners actually care about: reduced leakage, improved flow reliability, corrosion resistance, and (where designed) structural renewal.

ASTM F1743 is designed for rehabilitation across a broad set of applications (including sanitary sewers, storm sewers, process piping, conduits, and ventilation systems), which is another way of saying it’s a mainstream engineered method—not a fringe workaround.

When installations follow F1743 workmanship criteria—continuous over the installation length and free of dry spots, lifts, and delaminations—you’re targeting the failure modes that actually undermine CIPP performance: resin starvation, separation of layers, and loss of tight fit against the host pipe.

WHY IT’S LEGAL

“Legal” in construction means a permitted, inspected, standards-based method accepted in the jurisdiction where it is installed.

ASTM F1743 is expressly written for use not only by contractors, but also by designers/specifiers, regulatory agencies, owners, and inspection organizations involved in rehabilitation using pulled-in-place CIPP. That matters because it underscores what the standard is: a recognized practice that regulators and inspectors can evaluate against.

So the legality story is straightforward: when a CIPP project is permitted/inspected as required locally and the work is executed to ASTM F1743 workmanship and performance expectations, it is a standards-based installation—not an improvisation.

A PRACTICAL “COMPLIANCE” CHECKLIST THAT DOESN’T RELY ON BUZZWORDS

If you want to separate serious stop-and-start CIPP from marketing noise, ask for documentation that tracks directly to ASTM F1743 outcomes:

1)      Pre-install CCTV and cleaning verification (so the liner can fit tightly and cure correctly).

2)      Wet-out controls and resin tracking (to prevent dry spots).

3)      Cure monitoring and controlled cool-down (to reduce defect risk).

4)      Post-install CCTV demonstrating the finished liner condition (looking specifically for dry spots, lifts, and delaminations).

When you see those items in a project file, “gapping” stops being a debate term and becomes what it should be: a sequencing strategy that still produces a continuous, defect-free finished liner.

FAQs

Does ASTM F1743 require “continuous” lining?

-        ASTM F1743 treats “continuous” as a workmanship result: the finished CIPP should be continuous over the installation length and free of dry spots, lifts, and delaminations.

What does “continuous” mean in this context?

-        In ASTM F1743 workmanship terms, it is tied to liner integrity and the absence of defect conditions like dry spots (resin starvation), lifts (loss of tight fit/reverse curvature), and delaminations (layer separation).

Is stop-and-start CIPP safe?

-        Yes—when crews control access hazards, follow cure protocols, and verify the finished liner condition. ASTM F1743 addresses safety considerations for access structures and inspection expectations for defect conditions.

Is “gapping” legal?

-        When the work is permitted/inspected as required locally and executed to ASTM F1743 workmanship expectations, it is a standards-based method evaluated against a recognized practice used by regulators and inspection organizations.