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MASONRY-TO-SLAB JOINT · SEALING

Old masonry, new slab.
Water at the joint.

After the basement was deepened, a new slab met the existing masonry. Sealing required assessment of the cross-section, control of inflow and preparation of access to the joint.

Removing a floor strip beside the wall exposed the slab and provided access to the leaking joint.Material by Piotr Kobus, “Reverse Joint Context”, Injection(s) Case Studies. Fig. 2pkcs, p. 40.
Warsaw · building dating from 1913Basement refurbishmentBrick masonry + new concrete slab

01 · PROBLEM AND ASSESSMENT

Waterproof slab.
Leaking joint.

During refurbishment, the basement was deepened and a new waterproof concrete slab was constructed. The old brick walls remained supported on footings. Their junction with the new slab received no additional sealing. At high groundwater levels and after heavy rainfall, water appeared at the joint, periodically flooding the rooms.

Incomplete documentation and earlier alterations made the cross-section difficult to interpret. Exploratory holes revealed voids in the masonry. Removing a floor strip and pumping out water exposed the repair zone and revealed the actual inflow locations.

02 · DECISIONS AND WORK SEQUENCE

Each stage had a defined task

Substrate preparation, reduction of active flow and main injection formed a single repair sequence.

  1. 01 / PREPARATION

    Exposure and closure of defects

    Visible brick and mortar joint defects were initially closed with rapid-setting mortar. Holes were drilled through the slab towards the masonry, and packers were installed.

    CrackOn.5 →
  2. 02 / PRELIMINARY INJECTION

    Controlling inflow and voids

    WaterStopper was injected into the joint zone and masonry voids. Local seepage remained after this stage — reduced inflow allowed work to continue.

    WaterStopper →
  3. 03 / MAIN INJECTION

    Sealing the remaining water paths

    HydroGum was used in the second stage. Pressure and material consumption were monitored during injection, adapting delivery to the structure's behaviour.

    HydroGum →
  4. 04 / FUTURE ACCESS

    Preparing for further intervention

    After injection and before floor reinstatement, hoses were laid for potential future work. Limited access and possible changes in ground and water conditions were taken into account.

ACCESS AFTER THE REPAIR

Hoses prepared for future intervention

Hoses were laid after the main HydroGum injection and before floor reinstatement. They provided prepared access for possible later material delivery.

Injection hoses — planning access →
Hoses were laid after injection, preparing access for possible later material delivery. This stage preceded floor reinstatement.Material by Piotr Kobus, “Reverse Joint Context”, Injection(s) Case Studies. Fig. 4pkcs, p. 43.

03 · RESULT AND LESSON

Joint assessment determines the repair scope

Watertightness achieved, as reported by the author

Piotr Kobus reports complete watertightness after the main injection. The waterproof concrete floor layer was then reinstated, allowing room refurbishment to continue.

The water resistance of a new slab alone does not ensure a watertight junction with old masonry. In this case, the solution also addressed voids, inflow paths and access after refurbishment. This scope must be considered when planning the method.

Source: Piotr Kobus, “Reverse Joint Context”, Injection(s) Case Studies, pp. 37–44. Adapted from the author's case study of ResinBau product applications.

CASE RECORD

From inflow assessment to floor reinstatement

Water in the basement before sealing. The assessment covered the actual inflow path at the junction of old masonry and the new slab.Material by Piotr Kobus, “Reverse Joint Context”, Injection(s) Case Studies. Fig. 1pkcs, p. 38.
Preliminary WaterStopper injection covered masonry voids and the slab joint zone. Its purpose was to reduce active inflow before the main sealing stage.Material by Piotr Kobus, “Reverse Joint Context”, Injection(s) Case Studies. Fig. 3pkcs, p. 41.
Rooms after sealing and floor reinstatement, before further refurbishment work.Material by Piotr Kobus, “Reverse Joint Context”, Injection(s) Case Studies. Fig. 5pkcs, p. 44.

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