Waterproofing & Water Ingress

Penetrating Damp

Penetrating damp is the lateral movement of water through external walls driven by wind-driven rain, hydrostatic pressure against below-ground walls and water ponding at wall bases. Unlike rising damp, which moves upward through capillary action, penetrating damp tracks horizontally through the building fabric via cracks, failed mortar joints, defective sealants, window perimeter failures and porous masonry. It is one of the most common causes of water ingress complaints in strata buildings across coastal and high-rainfall areas of Australia.

Common Signs

Damp patches appearing on internal walls during or after rain
Water staining around window and door frames
Damp areas at the base of external walls
Paint blistering and peeling on internal wall surfaces
Salt efflorescence on external masonry and render
Mould growth on internal wall faces and behind furniture
Open or crumbling mortar joints on the external elevation
Persistent horizontal damp band or mould growth at skirting board level on external-facing walls in masonry construction — a characteristic sign of absent or failed base cavity flashing where water in the cavity has no drainage path and migrates through the inner skin at its base

Common Causes

Failed or absent sealants at window and door perimeters
Open or deteriorated mortar joints in masonry walls
Cracked or delaminated external render
Porous or highly absorbent masonry units
Missing or failed flashings over windows and lintels
Cavity wall ties corroding and carrying water across the cavity
Cavity fill bridging the clear cavity and providing a moisture path
Absent or failed base cavity wall flashing — where no continuous DPC membrane or metal flashing was installed at the base of the outer masonry leaf, or the original flashing has corroded, perforated or been mortar-bridged during construction, water descending the cavity face has no drainage path to weep holes and migrates through the inner skin. Required under AS 3700, AS 2904 and NCC 2022 Part 5.7, absent base cavity flashing is one of the most frequently undiagnosed causes of chronic damp and mould at skirting board level in older cavity masonry construction

Risk of Neglect

Progressive deterioration of masonry, mortar joints and render.
Damage to internal plaster, paint, flooring and furnishings.
Mould growth within the wall cavity and on internal surfaces.
Salt damage and staining on both internal and external faces.
Structural corrosion of embedded wall ties in cavity wall construction.
Ongoing amenity impact and resident complaints in strata buildings.
Escalating repair cost from delayed treatment of the underlying water entry.

Inspection Requirements

Map all affected internal wall areas, noting the relationship to external elements such as windows, lintels and mortar joints.
Inspect the external wall for cracks, failed render, open mortar joints, deteriorated sealants and exposed masonry.
Check window and door perimeter sealants, flashings and sills for failure, gaps and incorrect installation.
Assess the relationship between the damp area and weather exposure — penetrating damp is typically worse on the windward elevation.
Probe mortar joints to assess depth of deterioration and the porosity of the masonry units.
Inspect cavity walls for the presence of wall ties carrying moisture across the cavity and cavity fill that may be bridging.
In masonry cavity wall construction, inspect the first perpendicular mortar joints above floor level on the external face for functional weep holes at the correct spacing — their absence is a strong indicator that no cavity base flashing was installed. Confirm by carefully removing a single brick course in an inconspicuous location to expose the cavity base and inspect for the presence, material and condition of the DPC or metal flashing.
Review evidence of water penetration only appearing during or after rain events to differentiate from rising damp and condensation.
Consider a water hose test on the external face to replicate and confirm the water entry path.

Start Inspection Checklist

Create a project inspection record, add defect locations, upload photos, and save notes for scope writing.

Typical Repair Methodology

Penetrating damp repair must target the specific water entry path. The methodology below covers a typical external masonry wall treatment and internal reinstatement sequence.

01.Confirm the diagnosis and water entry path with a building consultant before commencing works.
02.Repair all external cracks in masonry, render and concrete elements using compatible crack repair mortars or flexible sealants.
03.Rake out and repoint all failed, open or deteriorated mortar joints with a mortar compatible with the existing masonry — avoid excessively hard mortars on older softer brick.
04.Replace failed sealants at all window and door perimeters using a compatible low-modulus silicone or polyurethane sealant over a correctly sized backing rod.
05.Inspect and reinstate all window and door head flashings where absent or displaced, ensuring correct laps and falls to drain water away from the wall face.
06.Apply a penetrating silane or siloxane water repellent treatment to the full external face of the affected masonry elevation.
07.Ensure the water repellent is applied to clean, dry masonry and allowed to penetrate fully before the surface becomes wet.
08.Where the masonry face is too deteriorated for water repellent alone, apply a compatible textured render or masonry coating system.
09.Remove any external elements bridging the cavity — check and clear cavity weep holes to allow drainage.
10.Where cavity base wall flashing is confirmed absent or non-functional: engage a licensed bricklayer to carefully remove the affected section of the outer masonry leaf in working sections of approximately one metre, staging and recording each brick for reinstatement. Clean all mortar debris from the cavity and prepare the inner leaf face.
11.Install a new continuous cavity base flashing — flexible polyethylene DPC membrane, lead, or aluminium — in compliance with AS 3700, AS 2904 and NCC 2022 Part 5.7. The flashing must be a minimum of 20 mm wider than the masonry leaf, turned up and bonded against the inner leaf face, and extend to the outer face of the wall with a formed drip edge or turn-down to direct water clear. Fix at 600 mm centres with a minimum 150 mm lap at all joints.
12.Reinstate brickwork over the new flashing using mortar matched to the existing in type and compressive strength to avoid stress concentration on the surrounding masonry. Form open weep holes at maximum 1200 mm centres in the first perpendicular mortar joint above the flashing, in accordance with NCC 2022 Part 5.3.
13.Remove internal plaster and finishes affected by moisture — allow the wall to dry fully before reinstating with a breathable plaster or render.
14.Reinstate internal finishes using breathable paints and materials compatible with residual moisture vapour movement.
15.Monitor the repaired areas for recurrence over one to two full winter seasons before closing out the defect.

Related Repair Systems

Masonry water repellent treatment systems
Repointing and mortar repair systems
External render and coating systems
Window and door perimeter sealing systems
Cavity wall drainage and flashing systems

Open Repair Systems →