What is a Adhesion Failure

Adhesion failure is the loss of bonding between a pipe rehabilitation material and the internal surface of the existing pipe. It occurs when a coating, resin, repair patch or bonded lining separates from the host pipe, either locally or across a larger area. This separation can reduce the effectiveness of the repair by allowing water to penetrate behind the material, creating pathways for leakage or exposing the original pipe surface to further deterioration.

In drainage and sewer rehabilitation, adhesion failure is particularly relevant to spray-applied coatings, bonded repair systems and certain lining technologies that depend on contact with the original pipe wall. The consequences depend on the material, the extent of separation and the purpose of the rehabilitation. A small area of debonding in a protective coating may have different implications from separation affecting a repair intended to restore watertightness.

Not all pipe liners require adhesion to function. Some cured-in-place pipe (CIPP) liners are designed to form a structurally independent or close-fitting pipe within the existing drain, without relying on a continuous adhesive bond. For these systems, a gap between the liner and host pipe does not automatically represent adhesion failure, although excessive gaps or other installation defects may still require investigation.

Adhesion in Different Pipe Rehabilitation Systems

Adhesion is the mechanism by which one material remains bonded to another through physical and chemical interactions at their interface. In pipe rehabilitation, the interface is usually between a prepared internal pipe surface and the repair material applied to it. The required bond strength depends on the product, substrate and loads the repaired section is expected to withstand.

Epoxy and polyurethane coatings are examples of systems where adhesion may be important. These materials can be applied to suitable prepared pipe surfaces to provide a protective or sealing layer. If the coating loses contact with the underlying material, water or contaminants may enter behind it, reducing the effectiveness of the protection.

Cementitious rehabilitation materials can also depend on adequate bonding to the existing substrate. Their performance is influenced by surface preparation, moisture conditions, material compatibility and curing. Poor adhesion may lead to hollow areas, cracking or detachment, particularly where the repair is exposed to groundwater pressure or movement.

Localised repair systems require separate consideration. A bonded repair patch may rely partly on adhesion to maintain its position and sealing performance, while another patch system may achieve its intended function through mechanical confinement and the cured material’s structural properties.

The main distinctions are summarised below.

A critical distinction exists between adhesion failure and delamination. Adhesion failure describes separation at the interface between the host pipe and the applied material. Delamination can describe separation between layers within a composite liner, which is a different defect with potentially different structural consequences.

The distinction is particularly important during CCTV surveys. A visible gap at the edge of a liner, a blister within a coating and separation between laminate layers should not automatically receive the same diagnosis. The rehabilitation method must be identified before the defect can be interpreted correctly.

Why Pipe Linings and Repair Materials Lose Adhesion

Successful bonding requires the repair material to make suitable contact with a compatible substrate. In drainage systems, this can be difficult because pipe interiors may contain grease, sediment, corrosion products, biological deposits and moisture. Existing pipe materials also vary considerably in surface texture, porosity and chemical characteristics.

Surface contamination is a major cause of poor adhesion. Fats, oils and grease can form a barrier between the pipe wall and a coating, preventing the repair material from bonding properly. Cleaning may remove visible deposits while leaving a thin film that continues to interfere with adhesion.

Moisture can also affect performance, particularly when a product requires a dry or specifically conditioned substrate. Active infiltration through cracks or displaced joints may introduce water during application or curing. Some rehabilitation products are formulated for damp conditions, but this does not mean they can tolerate unrestricted groundwater entry.

Common causes of adhesion failure include:

• Inadequate surface preparation. Grease, biofilm, loose deposits or deteriorated pipe material remain beneath the repair.

• Unsuitable substrate conditions. The original pipe surface is too weak, unstable or incompatible with the bonding material.

• Incorrect material preparation. Mixing proportions, application timing or handling conditions do not meet product requirements.

• Incomplete curing. Temperature, moisture or curing time prevents the material from developing its intended properties.

• Excessive groundwater pressure. Water enters behind the lining through cracks, joints or other openings.

• Thermal movement. Differences in expansion and contraction create stress at the bonded interface.

• Structural movement. Settlement, joint displacement or deformation imposes loads the bond cannot accommodate.

These factors can act together. For example, an older concrete sewer may have a weakened internal surface and several leaking joints. Applying a bonded coating without addressing these conditions may leave it attached to unstable material while groundwater continues to enter behind the repaired surface.

Temperature is another installation variable. Resin viscosity, working time and curing behaviour can change with temperature, sometimes considerably. A material applied outside its specified temperature range may not develop the physical properties or bond strength demonstrated under controlled conditions.

Even a correctly applied lining may experience subsequent stresses. Wastewater chemistry, cleaning operations, abrasion and repeated hydraulic loading can affect certain protective materials over time. Resistance to these conditions must be established for the particular rehabilitation system rather than assumed from the generic description of the resin.

How Adhesion Failure Develops Inside a Drain

Adhesion failure may begin in a small area where the original bond is weak or where water enters the interface. Once separation develops, hydraulic pressure, moisture migration or continued movement can increase the affected area. The progression depends on whether the lining remains mechanically stable and whether the underlying pipe continues to deteriorate.

One characteristic defect is blistering. A bonded coating may lift away from the pipe wall and form a raised area when pressure or another mechanism acts between the coating and substrate. The blister may remain intact initially, but subsequent loading or deterioration can cause cracking or rupture.

Peeling is another possible manifestation. Where the edge of a coating or bonded repair becomes detached, flowing water or mechanical contact may contribute to further separation. This is particularly relevant where the exposed edge faces the direction of flow or where cleaning equipment can catch the loose material.

In a gravity sewer, detached material can also affect hydraulic performance. A coating that projects into the pipe may trap wipes, sediment or other solids, creating a local obstruction. Fragments that break away can move downstream and accumulate at bends, junctions or existing restrictions.

The consequences are not limited to blockages. If the repair was intended to seal cracks or defective joints, loss of adhesion may reopen a pathway for groundwater infiltration or wastewater exfiltration. Water movement can also contribute to deterioration behind the coating, especially where the host pipe material is already damaged.

In pressurised pipelines, the conditions can be different. Internal pressure variations may affect the lining, while pressure reversal or external groundwater pressure can place additional demands on the bonded interface. The relevant failure mechanism depends on the pipe design and the way the rehabilitation system resists these loads.

A visually detached coating does not necessarily mean the host pipe has lost structural integrity. Conversely, a coating that appears intact from the inside may conceal deterioration of the underlying substrate. The condition of the repair and the condition of the original pipe must therefore be assessed separately.

Identifying Adhesion Failure During Drainage Inspections

CCTV inspection is often the first method used to investigate suspected rehabilitation defects in accessible drainage pipes. A camera can identify visible coating irregularities, raised sections, loose edges, cracks and material projecting into the flow. It can also document whether defects occur near joints, bends, lateral connections or other locations where the lining may be exposed to additional stresses.

However, CCTV inspection cannot directly measure bond strength. A smooth-looking coating may contain areas of poor adhesion that have not yet produced visible deformation. Equally, an apparent gap beside a structurally independent liner may be compatible with the original rehabilitation design.

The interpretation should account for the installed system, the condition before rehabilitation and the observations made during commissioning. Installation records may contain information about cleaning, surface preparation, groundwater control, application conditions and curing. These records can help identify whether a suspected defect is related to installation or developed later.

Where the condition of a bonded lining is critical, more detailed investigation may be required. Depending on the product and access available, this could involve examining exposed material, removing a representative sample or performing an appropriate adhesion test. Destructive tests must be planned carefully because they may damage a lining that is otherwise functional.

Pull-off adhesion testing is one method used to assess the strength of certain bonded coatings on accessible substrates. The test applies a controlled tensile load to a defined area and records the force required to produce failure. The result must be interpreted alongside the failure location, since the coating, adhesive interface or underlying substrate may fail first.

Such tests are not automatically suitable for every buried drainage lining. Limited access, curved surfaces and the risk of damaging the repair can restrict their use. Acceptance criteria should come from the relevant system specification rather than an arbitrary universal bond-strength value.

A useful investigation should establish whether the observed problem is:

1. Separation between the coating and the host pipe.

2. Separation between layers within a composite lining.

3. Cracking or deterioration of the rehabilitation material itself.

4. Failure of the original pipe beneath an otherwise intact lining.

5. An expected interface condition associated with a non-bonded lining system.

These distinctions determine whether the defect affects appearance, hydraulic performance, watertightness or structural capacity. They also help prevent unnecessary replacement of a lining that was never designed to adhere continuously to the host pipe.

Repairing Failed Adhesion and Preventing Recurrence

The appropriate response to adhesion failure depends on the size of the affected area, the repair material and the condition of the original pipe. A small local defect in an otherwise sound bonded coating may be suitable for a manufacturer-approved repair. Widespread separation can indicate a more fundamental problem with surface preparation, material compatibility or operating conditions.

Local repair commonly requires removal of loose material and preparation of a sound substrate. The replacement coating or repair compound must be compatible with the existing system, and the application must follow the required preparation and curing procedures. Applying fresh resin over detached material will not restore the missing bond to the host pipe.

Where groundwater is entering through the pipe wall, the infiltration may need to be controlled before a bonded repair can succeed. Otherwise, water may continue to act behind the new material. The method used to address infiltration must be suitable for the pipe and the rehabilitation specification.

If the original substrate has deteriorated substantially, repeating the same bonded repair may be ineffective. For example, a coating applied to weak or crumbling concrete cannot restore the underlying material’s strength simply by adhering to its surface. Structural rehabilitation may be necessary where the host pipe can no longer provide the support required by the proposed repair.

Prevention starts with selecting a rehabilitation system suited to the condition and function of the pipe. For bonded applications, cleaning alone is not always sufficient; the surface must also have the required strength, texture and moisture condition. The installer should establish that these conditions are achievable before application begins.

Quality control should cover material preparation, application thickness, environmental conditions and curing. Where the specification requires adhesion testing or other acceptance checks, these should be carried out using appropriate methods and documented results. Particular attention is needed at pipe joints, lateral connections and transitions between different materials.

A repair’s success ultimately depends on whether the selected technology requires bonding and whether that bond can remain effective under the expected service conditions. For coatings and bonded repair systems, separation at the pipe wall can directly undermine sealing and protective performance. For structurally independent liners, the more important assessment may instead concern liner integrity, deformation, connections and the loads the rehabilitated pipe must withstand.