Waterproofing

RJ Evans provides waterproofing systems to prevent water penetration through roofs, decks, balconies, terraces, podiums, buried structures, and other exposed or moisture-sensitive areas of buildings. Waterproofing is the creation of a continuous barrier designed to prevent uncontrolled water from passing through the protected construction and reaching substrates, insulation, structural components, internal finishes, or occupied areas. A waterproofing system must remain continuous across both the main surface and every detail where the protected area changes direction, terminates, drains, moves, or connects with adjoining construction. Upstands, outlets, penetrations, movement joints, edges, thresholds, flashings, changes in level, and interfaces between different materials can all interrupt the waterproof barrier if they are not incorporated correctly into the system.

The complete waterproofing assembly may include membranes, liquid-applied systems, mastic asphalt, primers, reinforcement, protection layers, drainage components, insulation, vapour-control layers, substrates, flashings, terminations, and associated detailing. The appropriate construction depends on the area being protected, the substrate, expected water exposure, movement, drainage requirements, access, loading, existing construction, and the way the waterproofing must connect with surrounding building elements. Waterproofing should therefore be considered as a complete water-exclusion system rather than as an isolated membrane, coating, or surface treatment. The performance of the protected area depends on continuity between the principal waterproofing layer, its terminations, drainage points, penetrations, interfaces, and adjoining details so that water is controlled across the complete construction. RJ Evans approaches waterproofing with the primary objective of achieving reliable water exclusion while protecting the underlying building fabric throughout the intended service life of the construction. The required system should provide continuous, compatible, correctly detailed, and appropriately drained protection so that water is prevented from reaching components that depend on the waterproof barrier for their continued performance and durability.

When Is Waterproofing Required?

Waterproofing is required where a building element is exposed to water in a way that could allow penetration into substrates, insulation, structural components, internal finishes, or occupied areas. The requirement depends on how water reaches the construction, whether it can collect or remain against the surface, how the protected area drains, where the waterproofing is interrupted by details and interfaces, and what lies beneath or behind the barrier.

The waterproofing system must provide continuous protection across the complete area exposed to water rather than only across the principal surface. The main waterproof layer, junctions, penetrations, terminations, drainage points, changes in level, and adjoining construction must function together so that water cannot bypass the barrier through an unprotected detail.

Waterproofing may be required where:

1. Building surfaces are directly exposed to rainfall or external water.
2. Water can collect, flow, or remain in contact with the construction.
3. The construction cannot rely on gravity and surface drainage alone to prevent water penetration.
4. Joints, penetrations, terminations, or interfaces interrupt the protected surface.
5. Occupied or moisture-sensitive construction is located beneath or behind the exposed area.
6. An existing waterproof barrier has lost the continuity required to exclude water reliably.

1. Building Surfaces Are Directly Exposed to Rainfall or External Water

Direct water exposure → the construction requires a continuous barrier against water penetration.

Roofs, balconies, terraces, podiums, decks, and other externally exposed building elements receive rainfall directly and must prevent water from passing into the underlying construction. The waterproofing system must remain continuous across the main surface and around every upstand, outlet, penetration, edge, termination, and adjoining element through which water could otherwise bypass the protected area.

2. Water Can Collect, Flow, or Remain in Contact With the Construction

Standing, flowing, or retained water → the waterproofing system must remain effective under the expected exposure conditions.

Water may accumulate temporarily on horizontal or low-slope surfaces, flow towards drainage points, concentrate around outlets and changes in level, or remain against buried, retaining, or otherwise enclosed construction. These conditions increase the duration or concentration of exposure and can place greater demands on joints, interfaces, terminations, and changes in construction. The waterproofing system must therefore be suitable for the way water reaches, remains on, and leaves the protected area.

3. The Construction Cannot Rely on Gravity and Surface Drainage Alone to Prevent Water Penetration

Limited natural water shedding → a dedicated waterproofing barrier is required to protect the construction.

Horizontal surfaces, low falls, recessed areas, buried construction, podiums, balconies, terraces, and similar elements cannot always shed water immediately through gravity alone. Water may remain on or against the construction while it moves towards an outlet, drainage layer, discharge point, or surrounding ground. In these situations, the protected construction requires a continuous waterproofing system capable of resisting water during the period of exposure rather than relying solely on rapid surface run-off.

4. Joints, Penetrations, Terminations, or Interfaces Interrupt the Protected Surface

Interrupted waterproofing plane → every transition must be incorporated into the continuous water-exclusion system.

Pipes, ducts, outlets, movement joints, thresholds, rooflights, plant supports, parapets, wall junctions, edges, changes in material, and changes in level interrupt the main waterproofing surface. These details can create water-entry routes where the waterproofing is discontinuous, inadequately terminated, incompatible with adjoining materials, or unable to accommodate expected movement. The waterproof barrier must therefore continue through each junction and transition rather than protecting only the principal field area.

5. Occupied or Moisture-Sensitive Construction Is Located Beneath or Behind the Exposed Area

Water-sensitive construction or occupied space → reliable waterproofing is required to protect the underlying building fabric.

Water penetration can affect insulation, structural decks, concrete, timber, boards, fixings, finishes, electrical services, stored materials, and occupied areas located beneath or behind the protected construction. Where uncontrolled water could damage these components, reduce their performance, or disrupt use of the building, the waterproofing system must prevent water from reaching them throughout the complete exposed area.

6. An Existing Waterproof Barrier Has Lost the Continuity Required to Exclude Water Reliably

Loss of waterproofing continuity → continuous water exclusion must be restored.

An existing waterproofing system may cease to provide reliable protection where cracking, splitting, blistering, loss of adhesion, failed joints, damaged surfaces, defective terminations, punctures, movement, deteriorated flashings, or incompatible previous work interrupts the barrier. Where the system can no longer prevent water from reaching the underlying construction, corrective waterproofing is required to restore continuity across the affected area and its adjoining details.

Waterproofing is therefore required where the expected water exposure and building construction create a credible route for uncontrolled water penetration. The system must provide continuous protection across the principal surface, drainage points, penetrations, terminations, junctions, and adjoining interfaces so that the protected construction remains isolated from water throughout its intended service condition.

When Are Repairs Required Before Waterproofing?

Existing construction may remain suitable for waterproofing even where localised defects are present. However, any condition that could prevent adhesion, interrupt waterproofing continuity, retain damaging moisture, restrict drainage, create uncontrolled movement, or leave an unstable substrate must be corrected before the waterproofing system is installed.

Repairs may be required where:

1. The substrate is cracked, damaged, unstable, or locally deteriorated.
2. Existing waterproofing contains defects that cannot be retained beneath the proposed system.
3. Insulation, boards, screeds, decks, or other components contain localised moisture damage.
4. Joints, upstands, edges, penetrations, or terminations are defective.
5. Falls, outlets, drainage routes, or water-management details are not functioning correctly.
6. Previous repairs, coatings, sealants, or retained materials are unstable or incompatible.

1. The Substrate Is Cracked, Damaged, Unstable, or Locally Deteriorated

Defective supporting substrate → damaged or unstable areas must be repaired before waterproofing proceeds.

Concrete, screeds, boards, decks, masonry, asphalt, existing membranes, and other substrates must provide a sufficiently sound and stable base for the proposed waterproofing system. Cracks, spalling, loose surfaces, damaged boards, localised decay, corrosion, voids, friable materials, or excessive movement can prevent reliable adhesion or transfer defects into the new waterproofing layer. Affected areas should be repaired, replaced, stabilised, or otherwise prepared so that the completed system is supported by dependable construction.

2. Existing Waterproofing Contains Defects That Cannot Be Retained Beneath the Proposed System

Unstable existing waterproofing → defective areas must be repaired or removed before the new barrier is installed.

Existing membranes, coatings, mastic asphalt, and other waterproofing materials may contain splits, blisters, open joints, delamination, punctures, failed laps, loss of adhesion, or localised deterioration. Where these defects create instability, uncontrolled movement, moisture pathways, or an unreliable base, they should not simply be concealed beneath the proposed system. Defective areas must be corrected so that any retained waterproofing forms part of a stable and serviceable construction.

3. Roof or Building Components Contain Localised Moisture Damage

Localised wet or moisture-damaged components → affected materials must be addressed before they are enclosed by new waterproofing.

Water may become retained within insulation, cover boards, screeds, decks, existing membranes, or other concealed materials. Moisture can reduce thermal performance, contribute to deterioration, affect adhesion, and remain trapped once a new waterproof barrier is installed. Where damage is confined to identifiable areas, affected components should be exposed and assessed, with materials that cannot remain serviceable removed, dried, repaired, or replaced as required.

4. Joints, Upstands, Edges, Penetrations, or Terminations Are Defective

Defective waterproofing interfaces → vulnerable details must be corrected so the new barrier can remain continuous.

Water commonly enters where the main waterproofing surface meets walls, parapets, thresholds, outlets, pipes, ducts, movement joints, kerbs, edges, and adjoining materials. Open joints, inadequate upstands, loose flashings, failed seals, damaged terminations, unsupported edges, and poorly formed transitions can prevent the proposed system from terminating securely. These details must be reconstructed or corrected so that waterproofing continuity can be maintained through every junction.

5. Falls, Outlets, Drainage Routes, or Water-Management Details Are Not Functioning Correctly

Defective water management → drainage conditions must be corrected so water can be controlled across the completed system.

Blocked or inadequate outlets, defective gutters, deteriorated drainage channels, insufficient falls, localised low points, restricted discharge routes, and poorly positioned drainage points can cause water to collect or remain against the waterproofed construction. These conditions may require cleaning, repair, outlet modification, localised levelling, drainage alteration, or reconstruction before waterproofing is completed. The finished system should both exclude water and direct it towards suitable drainage or discharge points.

6. Previous Repairs, Coatings, Sealants, or Retained Materials Are Unstable or Incompatible

Unsuitable retained materials → defective or incompatible layers must be removed, isolated, or correctly prepared.

Old coatings, sealants, patches, primers, bituminous materials, adhesives, unidentified compounds, contaminants, and previous repair systems may prevent the proposed waterproofing from bonding or performing consistently. Loose materials must be removed, retained surfaces should be assessed for compatibility, and unsuitable areas should be cleaned, prepared, primed, isolated, or replaced in accordance with the requirements of the selected waterproofing system.

All required repairs should be completed before the new waterproofing membrane, coating, mastic asphalt, or liquid-applied system is installed. Waterproofing should protect construction that is sound, suitably dry, stable, correctly drained, compatible, and properly detailed rather than conceal defects that could continue to cause water ingress, instability, loss of adhesion, or premature failure beneath the completed system.

When Is a Waterproofing Overlay Not Appropriate?

A waterproofing overlay is only one possible method of restoring or upgrading an existing waterproof barrier. It is not appropriate where the retained construction cannot provide a dry, stable, compatible, adequately supported, correctly detailed, and properly drained base for the proposed system. An area may still be capable of waterproofing through partial removal, reconstruction, or complete replacement, but defective construction should not be concealed beneath an additional membrane, coating, mastic asphalt, or liquid-applied system.

A waterproofing overlay is not appropriate where:

1. Moisture is widespread within the existing construction or waterproofing build-up.
2. The retained substrate or existing waterproofing is unstable.
3. The existing surface is contaminated or incompatible with the proposed system.
4. The supporting construction is defective or subject to uncontrolled movement.
5. Drainage, falls, levels, or termination constraints cannot be corrected within the retained build-up.
6. Multiple existing layers prevent reliable assessment or installation.

1. Moisture Is Widespread Within the Existing Construction or Waterproofing Build-Up

Widespread trapped moisture → the affected construction should not be covered by a new waterproofing overlay.

Moisture may extend through insulation, screeds, cover boards, decks, membranes, vapour-control layers, joints, or other concealed components. Installing a new waterproof barrier above saturated or moisture-damaged materials can trap water within the construction, impair adhesion, reduce thermal performance, contribute to continuing deterioration, and conceal the true extent of the defect. Wet or damaged components must be exposed and assessed, with materials that cannot remain serviceable removed, dried, repaired, or replaced before waterproofing proceeds.

2. The Retained Substrate or Existing Waterproofing Is Unstable

Loose or failing retained construction → the proposed overlay would depend on an unreliable base.

Widespread blistering, delamination, loss of adhesion, loose membranes, unstable coatings, friable screeds, damaged boards, cracking, soft areas, or deteriorated substrates can prevent the proposed waterproofing from performing consistently. An overlay cannot compensate for construction that is separating, moving, or losing integrity beneath it. Defective materials must be removed, stabilised, repaired, or replaced until the retained construction can provide a dependable base for the new system.

3. The Existing Surface Is Contaminated or Incompatible With the Proposed System

Unreliable adhesion or material compatibility → the proposed waterproofing overlay cannot be installed dependably.

Oils, release agents, persistent contamination, incompatible coatings, unidentified sealants, bituminous residues, previous repair compounds, or chemically unsuitable materials may prevent reliable adhesion or interact adversely with the proposed waterproofing system. Where cleaning, preparation, priming, compatibility testing, or isolation cannot provide a suitable interface, the affected materials should be removed rather than retained beneath the new waterproofing.

4. The Supporting Construction Is Defective or Subject to Uncontrolled Movement

Structural or substrate instability → a surface-applied waterproofing system cannot restore the integrity of the supporting construction.

Severe cracking, excessive movement, deflection, settlement, corrosion, decay, damaged decking, failed screeds, loose masonry, or widespread loss of support can cause the waterproofing layer to split, detach, deform, or fail at adjoining details. Waterproofing should not be expected to compensate for deterioration or movement beyond the capability of the selected system. The supporting construction must be repaired or reconstructed before the waterproof barrier is installed.

5. Drainage, Falls, Levels, or Termination Constraints Cannot Be Corrected Within the Retained Build-Up

Unresolvable drainage or level constraints → the existing construction must be modified or rebuilt before waterproofing proceeds.

Inadequate falls, persistent low points, restricted outlets, insufficient upstand heights, limited threshold clearances, poorly positioned drainage points, or unsuitable finished levels can prevent the completed waterproofing from draining and terminating correctly. Where these conditions cannot be corrected through local preparation, levelling, drainage modification, or detailing, part or all of the existing build-up may need to be removed or reconstructed so that the new system can form a continuous and correctly drained waterproof barrier.

6. Multiple Existing Layers Prevent Reliable Assessment or Installation

Unknown or inconsistent retained construction → further overlaying may preserve concealed defects and unreliable interfaces.

Several generations of membranes, coatings, screeds, insulation, sealants, patches, overlays, and previous repairs can make it difficult to confirm moisture condition, adhesion, compatibility, movement, attachment, and the actual construction beneath the visible surface. Additional overlaying may retain concealed deterioration or introduce another interface whose performance cannot be established reliably. Opening-up, selective removal, or complete removal may be required before a dependable waterproofing strategy can be defined.

A waterproofing overlay should only be installed where the retained construction provides a dry, stable, compatible, adequately supported, correctly detailed, and properly drained base for the proposed system. Where these conditions cannot be achieved while retaining the existing build-up, the defective construction should be removed or reconstructed rather than concealed beneath additional waterproofing layers.

When Is Partial or Complete Waterproofing Replacement Required?

Partial or complete waterproofing replacement is required where defective, moisture-damaged, unstable, incompatible, or deteriorated components cannot be retained reliably within the corrected waterproofing system. The extent of replacement depends on whether the identified failure remains confined to a defined area or affects the waterproofing and supporting construction as a complete assembly.

When Is Partial Waterproofing Replacement Appropriate?

Partial waterproofing replacement is appropriate where deterioration is too extensive for localised repair but remains confined to a clearly defined area. This may include one section of a roof, balcony, terrace, podium, deck, drainage zone, perimeter area, threshold, movement joint, penetration group, or adjoining waterproofed detail.

Partial waterproofing replacement may be required where:

1. Moisture damage is concentrated within a defined section of the waterproofed construction.
2. One area contains widespread membrane, coating, substrate, insulation, or supporting-layer failure.
3. A drainage zone, perimeter, threshold, movement joint, penetration group, or adjoining interface requires reconstruction.
4. A defined section cannot provide a reliable basis for continued repair or further overlay.

The defective section is removed and reconstructed before being connected to the retained waterproofing through compatible membranes, coatings, substrates, drainage components, joints, upstands, terminations, and adjoining interfaces. Partial replacement preserves serviceable areas while removing components that cannot remain reliably within the corrected waterproofing system.

When Is Complete Waterproofing Replacement Required?

Complete waterproofing replacement is required where deterioration, moisture damage, instability, incompatibility, or repeated failure affects the protected area as a complete waterproofing assembly. Replacement should be selected where retaining the existing system would leave widespread defective materials in place, conceal continuing moisture-related deterioration, or create an unreliable base for further repair, overlay, or refurbishment.

Complete waterproofing replacement may be required where:

1. The waterproofing membrane, coating, mastic asphalt, or other barrier contains widespread or advanced material failure.
2. Moisture extends across multiple areas or through substantial parts of the existing waterproofing build-up.
3. The substrate, insulation, screed, deck, or supporting construction is extensively deteriorated or unsuitable for retention.
4. Repeated repairs, patches, coatings, overlays, or previous waterproofing systems have created an inconsistent or unreliable assembly.
5. The required drainage, falls, levels, movement accommodation, upstands, interfaces, or termination details cannot be corrected reliably while retaining the existing waterproofing system.

Complete replacement allows the existing waterproofing build-up to be removed, concealed conditions to be exposed, and defective membranes, coatings, mastic asphalt, screeds, insulation, boards, substrates, drainage components, joints, and associated construction to be repaired or replaced. The new waterproofing can then be designed and installed as one coordinated system incorporating suitable substrates, continuous waterproofing layers, drainage, movement accommodation, penetrations, upstands, terminations, protection layers, and interfaces with adjoining construction.

RJ Evans determines the appropriate waterproofing pathway by assessing the protected area as a complete assembly. Where defects remain localised and the surrounding construction is dry, stable, compatible, correctly detailed, and serviceable, repair may restore waterproofing continuity. Where deterioration or moisture damage affects a defined section that cannot be retained reliably, partial replacement can reconstruct the affected area while preserving serviceable construction. Where deterioration, moisture, instability, incompatibility, or repeated failure affects the waterproofing system as a whole, complete replacement is required to restore continuous and reliable water exclusion.

Do You Need Waterproofing Repair, Refurbishment, or Replacement?

The correct waterproofing intervention depends on the condition of the existing barrier, substrate, drainage, interfaces, concealed construction, and the extent of any moisture damage or deterioration. A local defect may require only targeted repair, while wider failure can require refurbishment, partial reconstruction, or complete replacement of the waterproofing system. RJ Evans assesses waterproofed construction as a complete assembly to determine which components remain serviceable and which require corrective work. The assessment may consider the condition and continuity of the existing waterproofing, substrate stability, retained moisture, drainage performance, movement, penetrations, upstands, terminations, and adjoining interfaces before the remedial scope is defined.

Where the existing system remains dry, stable, compatible, and suitable for retention, repair or refurbishment may restore reliable water exclusion. Where deterioration or moisture damage affects a defined area, partial removal and reconstruction may be required. Where failure affects the waterproofing system as a complete assembly, complete replacement may provide the appropriate corrective solution. If you are experiencing water ingress, deterioration, failed waterproofing, or uncertainty about the condition of an existing system, contact RJ Evans to arrange an assessment and determine the appropriate repair, refurbishment, or replacement scope.