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.
Water staining on an internal wall consistent with penetrating damp through the external masonry.
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
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
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
Download Inspection Checklist- 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.
- 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.
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.Remove internal plaster and finishes affected by moisture — allow the wall to dry fully before reinstating with a breathable plaster or render.
- 11.Reinstate internal finishes using breathable paints and materials compatible with residual moisture vapour movement.
- 12.Monitor the repaired areas for recurrence over one to two full winter seasons before closing out the defect.
Before / After Repair
Typical penetrating damp condition before and after external repointing, sealant replacement and water repellent treatment.
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 →
Related Materials
- Silane and siloxane water repellents
- Low-modulus silicone and polyurethane sealants
- Repointing mortars and repair compounds
- Backing rods and bond breaker tapes
- Breathable masonry paints and renders
Open Materials →