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KNOWLEDGE · CONSTRUCTION AND EXPANSION JOINTS

Expansion joints: watertightness while retaining movement

The repair must stop water and retain joint movement. Plan the full filling zone, flow monitoring and a flexible finish.

AssessmentProcedure and optionsSelection and next step

EXPLORE THE METHOD

Expansion joint: from preparation to a watertight moving joint

The cross-section explains layer functions, while subsequent illustrations show preparation and separate injection options: gravity-fed, in a wall, in a suspended slab and beside a waterstop. Select the option matching the assessed joint; these are not operations all performed in every expansion joint.

The layers must retain material in the defined zone and preserve joint movement.

01 · Cross-section

Repair principle: deep filling and a flexible face

The blue band represents AcrylGel + Polymer filling. The lighter lower layer limits escape during further injection; the main layer lies above it. The Backer Rod supports the finish, and PU Sealant means the flexible compound at the face.

The drawing shows a solution for a specific geometry. Read the 120 mm label as a dimension of this option, not a universal repair depth. Cross-section, joint movement, water pressure and protection of the gel against drying determine the actual detail.

  • Establish filling boundaries and movement directions.
  • Distinguish the working seal from the final finish.
Material selection and joint movement →Volume of the assessed expansion joint →
Exposing the joint enables assessment of its actual cross-section.

02 · Preparation

Remove loose layers and ineffective compounds

Remove loose fragments and ineffective old compounds from the planned zone. Expose the joint using a method suited to edge condition, waterstop position and other joint components. The aim is to prepare a controlled space for filling.

Check whether removing layers reveals voids or additional flow paths. Do not damage sound sealing while trying to enlarge access.

  • Assess the exposed edges.
  • Mark revealed voids and previous repairs.
Injection zone boundaries →
Brushing removes residues that must not support the backing or seal.

03 · Preparation

Clean the joint surfaces

Clean deposits and residues from the previous stage off the joint sides and accessible base. Select the brush and method for the edge material. An even, assessed space makes backing placement and discharge restriction during injection easier.

Pay attention to areas concealed by old filling. Remaining loose fragments may change the flow path or hinder a durable finish.

  • Check the entire accessible depth.
  • Remove detached residues before continuing.
Preparing a confined zone →
Water in this illustration is used for cleaning before injection material enters the joint.

04 · Preparation

Flush dust and debris from the joint

Remove dust and debris left after cleaning. The option shown uses water; select flushing method and intensity for substrate and seal condition. Do not damage prepared edges.

Observe drainage. Water appearing beyond the planned section may indicate connection to a void or adjacent fissure. Account for that path before confining the zone and injecting material.

  • Check residue removal.
  • Record unintended drainage paths.
Water path assessment →
Four components form two working mixtures; check their reaction before injection.

05 · Preparation

Prepare two mixtures and check the reaction

The illustration separates A1 + A2 and B1 + B2. In the AcrylGel + Polymer variant, prepare two mixtures separately. The pump assembly delivers them through two lines; four product components do not mean four pump lines.

A trial under conditions similar to the works must confirm the time needed for material to reach the farther part of the joint. For the gravity-fed option, prepare a batch according to the product data sheet and its usable time. Shorter and longer reactions in subsequent illustrations describe layer functions, not a ready-made formulation.

  • Check product variant and trial temperature.
  • Record trial results before preparing a larger batch.
Mixing AcrylGel →Cleaning according to product chemistry →
Gravity-fed option: the shorter-reaction layer restricts escape of the next batch.

06 · Gravity-fed option

Top-open option: create a preliminary layer

This option concerns a joint accessible from above where the applied material can be retained. The lower gel layer with a shorter reaction time provides confinement for subsequent filling.

First confirm that the batch remains in the planned zone and is not carried away by water. Rapid material loss requires checking the drainage path and joint confinement before main application begins.

  • Check retention of the first batch.
  • Observe discharge beyond section boundaries.
Access depends on geometry →
The longer-reaction layer must spread within the confined cross-section.

07 · Gravity-fed option

Top-open option: fill the prepared space

Once material retention conditions are achieved, apply the main layer. In the drawing, SLOW-REACTING means gel with a longer reaction time that can fill the prepared space above the preliminary layer.

Monitor filling level and continuity along the joint. Material disappearing in an unknown direction is not proof of progress. After filling, leave space for the designed backing and flexible finish shown in the first cross-section.

  • Relate uptake to observed filling.
  • Retain space for the final detail.
Checking the full cross-section →
Points must deliver material to different cross-sectional zones and allow observation.

08 · Wall option

Wall option: drill access holes to the joint

Plan boreholes according to actual joint width and depth. Holes on both sides must provide access to the filling zone and observation points, not merely deliver material beside the visible face.

Account for waterstop, reinforcement and service positions. Ends and deeper joint areas must also be accessible for inspection. Drilling angle and length follow the assessed cross-section.

  • Confirm where the hole intersects the joint.
  • Provide access to section ends.
Access geometry →
Prepare a clear path from the packer to the target zone.

09 · Wall option

Wall option: clean the completed holes

Remove drilling debris from the holes. The illustration shows water flushing for this purpose; arrows do not represent the actual injection material. Check clear passage and communication locations before installing and connecting packers.

If water reaches beyond the assessed section, explain that path before sealing the face. Cleaning the hole entrance is insufficient if the farther section remains blocked.

  • Check the entire injection path.
  • Account for unintended communication.
Checking the full cross-section →
Backing and face sealing retain gel inside the planned band.

10 · Wall option

Wall option: confine the working zone

In the diagram, a rod deep in the joint and backing near the face define the working space. CrackOn.5 seals the face during injection. Observation points remain accessible to monitor communication between sections.

The seal must not conceal material escaping into an unknown void. The 120 mm label describes band width in this option; the actual dimension and permanent finish are established for the specific joint. The rigid seal is temporary here.

  • Check working boundary continuity.
  • Do not close every observation path.
Role of the working seal →
Communication to the next point confirms a connection, assessed together with uptake and pressure.

11 · Wall option

Wall option: track filling of successive sections

Inject in sections that allow material spread to be observed. The blue band represents the target filling zone, while discharge at the next point reveals a connection to the injection location.

Discharge or a pressure rise alone does not confirm complete filling. Compare quantities, communication locations and changes in water behaviour. If uncontrolled escape or a pressure rise without uptake occurs, stop injection and check the cause.

  • Record the sequence of material communication.
  • Check the whole band, not just the visible face.
Pressure, uptake and observation →
The end borehole covers the farther part of the expansion joint.

12 · Wall option

Wall option: deliver material to the end of the cross-section

The upper access shown leads to the end zone beside the suspended slab, which cannot be assessed solely from discharges below. Hole position and angle follow the joint path and its boundaries.

Check section ends and connections to adjacent seals. A remaining gap at an end may still carry water even if the middle appears filled. Do not copy an illustrative angle without assessing the detail.

  • Check the zone near the suspended slab and section boundaries.
  • Confirm access before drilling the last hole.
Expansion joint repair acceptance →
The preliminary layer prepares conditions for filling the deeper zone.

13 · Suspended slab option

Suspended slab option: restrict discharge with a shallower layer

With access from below, the first, shallower approach allows injection of shorter-reaction gel. A backer rod and temporary CrackOn.5 seal form the lower working boundary.

Check that material remains in this zone and available points allow flow observation. This option concerns access through a suspended slab; it is not another mandatory stage after filling the wall.

  • Distinguish shallower and deeper zones.
  • Confirm retention of the confining layer.
Selecting reaction time →
Deeper access allows material distribution beyond the zone near the face.

14 · Suspended slab option

Suspended slab option: fill the deeper cross-sectional zone

The second borehole leads to the main layer, where longer-reaction gel must spread through the prepared cross-section. Backing and the preliminary layer restrict escape from below.

Monitor communication to observation points and the ends of the sealed section. Select hole depth and position for actual slab geometry. The uniform image in the diagram is an objective whose achievement must be assessed during work.

  • Check communication in the deeper area.
  • Assess section ends before finishing injection.
Pressure, uptake and communication →
Rigid mortar needed during injection must not block joint movement.

15 · Completion

Remove the temporary seal

After injection, remove temporary mortar wherever it would restrict joint movement. Follow the final detail while preserving the actual filling deeper inside.

Check that no rigid bridges remain between edges. Prepare space for backing and a flexible finish; do not treat exposed gel as the final, unprotected surface.

  • Check the entire seal line.
  • Retain room for the flexible detail.
Inspection after filling →
The finish protects the sealing zone and must permit the intended movement.

16 · Completion

Form a flexible face and inspect the joint

Remove packers, prepare surfaces and seal the holes as specified. PU Sealant means the flexible compound at the face; its geometry and backing follow required movement and joint conditions.

Include protection of the gel against drying. Acceptance covers watertightness of the whole section, connections to adjacent seals and retained movement. A finished face does not replace inspection under representative water conditions.

  • Check continuity of the finish and connections.
  • Confirm watertightness and retained movement.
Repair acceptance →
Repair beside a waterstop requires a separate access detail.

17 · Waterstop option

Waterstop option: identify and fill cavities

The black ribbed wings represent the waterstop, and yellow areas represent voids at its interface with concrete. The drawing shows a specific option of drilling through the waterstop to an identified cavity. It does not instruct random drilling through sound sealing.

Material selection follows water conditions, the space to be filled and movement. HydroGum needs water to react and forms a foamed fill: distribution, confinement of expansion and retained joint movement must be confirmed. Flexible AcrylGel + Polymer gel is another option; do not automatically transfer the injection method between them.

  • Establish waterstop position and cavity extent.
  • Check injection effects on the waterstop and joint movement.
HydroGum: reaction conditions →AcrylGel + Polymer →
Deep injection and surface sealing serve different functions.

18 · Waterstop option

Waterstop option: monitor the top-up path

In this option, angled access directs material into the gap beside an existing or new PU finish. The CONTROL LEAK arrow marks a location for observing material communication; it does not mean a leak should remain after repair.

Observation must confirm that material reached the assessed zone beside the waterstop. After supplementary sealing, assess continuity along the entire section and complete the specified surface seal. Sealant at the face alone does not prove filling of deeper voids.

  • Relate the observation point to the injection zone.
  • Check watertightness after completing top-up injection.
Checking the full cross-section →Cleaning the system after the selected material →

Establish what must remain movable

Record joint width and depth, expected movement directions, edge condition and positions of the waterstop and previous fillings. Identify whether water flows through the expansion joint face, along the waterstop, through a cavity beside it or from an adjacent crack. Visible leakage may be far from the original defect.

Expansion joint movement follows the design and structural behaviour. Elongation at break of a resin specimen is not the allowable movement of the completed joint. Detail performance also depends on geometry, backing, adhesion, deformation mode and water conditions.

The material needs a confined space

Remove loose layers, deposits and ineffective compounds from the planned zone. Select backing and sealing to retain material at the correct depth while preserving observation points. Rapidly disappearing material may be leaving the expansion joint; simply increasing the batch does not control the filling location.

In the diagrams, a backer rod and temporary CrackOn.5 seal form working boundaries. Their positions follow the cross-section. Example sealing band dimensions should not replace detail selection for actual movement and water pressure.

Access depends on geometry

Open horizontal expansion joint

If the zone can be prepared and confined from above, consider controlled gravity application. A shorter-reaction layer can limit escape, while a subsequent longer-reaction layer allows distribution. A trial must confirm that water flow does not wash out the gel.

Expansion joint in a wall or suspended slab

Boreholes must reach planned levels and zone ends. Observation points allow communication along the joint and into the cross-section to be assessed. Injection only near the visible face may leave the farther part unsealed.

Leakage beside a waterstop

First identify the waterstop position and condition. Access to the space beside it is a separate repair detail. Do not randomly puncture sound sealing while searching for a leak.

Strong water inflow

Select an inflow-reduction stage to provide conditions for the main material. Retain space and access for further sealing; uncontrolled filling of the whole zone with fast foam may hinder the next stage.

Reaction time must match the material path

Prepare an AcrylGel trial at material and ambient temperatures similar to the works. A table time helps start selection but does not state how long material will flow in the actual joint. Too short a time may close the path before reaching the farther zone; too long may allow escape or washout.

The ResinBau AcrylGel + Polymer variant requires two mixtures and a suitable delivery assembly. The number of system components does not define the number of pump lines. For HydroGum, ensure water contact for the reaction and select delivery for the zone's moisture conditions. During reaction it forms a flexible foamed fill, so confinement of expansion, material distribution and retained required joint movement must be checked. Do not automatically transfer the HydroGum injection method from the gel option.

Observation covers the full cross-section

Start with a trial section. Record quantities, discharge sequence and changes in water behaviour. Communication to the next point confirms a connection; continue assessing ends, depth and possible escape. A pressure rise without uptake or uncontrolled discharge requires stopping and checking the cause.

After filling, remove temporary rigid bridges according to the detail and install the specified flexible finish. Include gel at an open face in the design for protection against drying. Do not leave working mortar as an element blocking expansion joint movement.

Finishing injection does not complete acceptance

Check watertightness of the entire section and its connections to adjacent seals. Acceptance should account for water pressure conditions and joint behaviour after movement relevant to service. Record material, formulation, temperature, trial result and completed finish.

The volume calculator helps order material for the assessed cross-section. It does not predict cavities beside the waterstop, migration along the interface or actual expansion of material confined within the structure.

RESINBAU SELECTION

Site conditions determine the material

ResinBau AcrylGel + Polymer →

The primary option for flexible filling of a prepared expansion joint. Select reaction time and protection against drying; do not automatically replace the polymer variant with the water variant.

HydroGum →

For zones with water needed for reaction and for limiting its flow. HydroGum forms a foamed fill during reaction; in an expansion joint, confirm confinement of its expansion, material distribution and retained required joint movement.

WaterStopper →

A stage reducing strong inflow before the selected main seal; not a rigid filling of a moving joint.

CrackOn.5 →

Temporary sealing during injection, removed where it would block designed movement.

Calculate what you know

CALCULATORExpansion joint volume →

Calculate the assessed cross-section; separate zones with different dimensions.

CALCULATORMaterial mixing →

Select the specific product and variant. Confirm reaction time with a trial.

CALCULATORLitres and kilograms →

Convert the correct material or mixture, accounting for the stated assumptions.

Next step

READ MOREInjection monitoring →

Combine pressure, uptake and material communication.

READ MORETunnel joints →

Account for water migration and division into sections.

Discuss your project conditions

Prepare a cross-section, a description of water and movement, and results of previous trials. ResinBau helps select the material and application method.

Discuss your project / technical selection ↗