1. Introduction
Liquid applied waterproofing is a specialist waterproofing system used extensively on commercial buildings, flat roofs, podiums, balconies, walkways, terraces and multi-storey car parks.
The system consists of liquid-applied resin, polymer, bitumen or other waterproofing materials that are applied directly to a suitably prepared substrate. Once cured, the liquid forms a continuous waterproof membrane across the surface.
Unlike traditional sheet membranes, which are manufactured in rolls and joined together on site, liquid applied waterproofing is formed in situ. This allows the system to follow the profile of the substrate and provide continuous protection around many complex details.
Liquid applied membranes are now widely used for both new construction and refurbishment. The versatility is a major advantage, with systems available for roofs, balconies, walkways, green roofs, podiums and car parks.
For commercial buildings and multi-storey car parks, waterproofing is particularly important because uncontrolled water penetration can cause deterioration of concrete, corrosion of reinforcement, damage to internal areas and increased maintenance requirements.
2. What Is Liquid Applied Waterproofing?
Liquid applied waterproofing is a waterproof membrane system applied to a prepared surface in liquid form.
Depending on the system, the waterproofing may be based on:
- Polyurethane
- Polyurea
- Polymethyl methacrylate (PMMA)
- Polyester resin
- Polymer-modified bitumen
- Acrylic or water-dispersible polymers
- Silane-modified polymers
- Other specialist liquid membrane technologies
Different systems have different properties and are selected according to the substrate, exposure, expected movement, traffic, temperature, chemical exposure and required service life.
There is a number of generic liquid membrane types and specifying systems supported by appropriate third-party accreditation, such as relevant Agrément or ETA certification, for the intended application.
A typical liquid waterproofing system may comprise:
- Substrate preparation
- Primer
- Reinforcement where required
- Waterproofing/base coat
- Additional waterproofing layers
- Topcoat or protective finish
- Slip-resistant or trafficable finish where required
The final system should always be installed in accordance with the manufacturer's approved specification.
3. Why Is Liquid Waterproofing Necessary?
The primary purpose of waterproofing is to prevent water from entering the building structure.
Water penetration can cause significant damage over time. In reinforced-concrete construction, water can penetrate through cracks, joints, porous concrete, failed waterproofing and defective details.
Once water enters the structure, it can contribute to:
- Reinforcement corrosion
- Concrete cracking
- Delamination
- Spalling
- Dampness
- Efflorescence
- Internal water damage
- Freeze-thaw deterioration
- Damage to finishes
- Corrosion of embedded components
The risk can be particularly high in multi-storey car parks.
Multi-storey car parks are exposed structures vulnerable to water, chemicals, chlorides and UV radiation. Vehicles can also introduce de-icing salts, while exhaust fumes and other contaminants can contribute to deterioration.
A properly designed waterproofing system therefore acts as a protective barrier between the environment and the underlying structure.
4. Liquid Waterproofing in Multi-Storey Car Parks
Multi-storey car parks provide a particularly demanding environment for waterproofing systems.
Car park decks may be exposed to:
- Rainwater
- Standing water
- Chlorides
- De-icing salts
- Vehicle fluids
- UV radiation
- Repeated vehicle loading
- Tyre abrasion
- Braking forces
- Temperature fluctuations
- Freeze-thaw conditions
Waterproofing failures at deck level can allow contaminated water to migrate into the concrete structure.
This can result in reinforcement corrosion and subsequent concrete deterioration.
Failed deck joints and poor surface waterproofing is identified as potential causes of water leakage to lower levels, which can contribute to reinforcement corrosion and compromise the integrity of the structure.
Liquid-applied systems can provide a seamless, elastomeric and durable surface capable of accommodating certain movement and cracking when correctly designed and installed.
5. How Liquid Waterproofing Works
Liquid waterproofing works by creating a continuous membrane over the substrate.
The liquid material is applied at a specified coverage or thickness and then cures to form a waterproof layer.
Because the membrane is formed in situ, it can be detailed around:
- Drainage outlets
- Upstands
- Parapets
- Pipe penetrations
- Columns
- Kerbs
- Thresholds
- Movement joints
- Plant supports
- Changes in level
- Complex roof geometry
This is one of the major advantages of liquid systems.
The absence of conventional sheet laps across large areas can also simplify certain detailing requirements. However, the membrane still requires carefully designed terminations, joints, penetrations and transitions.
6. Surface Preparation
Correct substrate preparation is fundamental to the performance of a liquid waterproofing system.
Before application, the substrate should be assessed for:
- Structural condition
- Cleanliness
- Moisture content
- Surface contamination
- Cracking
- Weak or friable material
- Existing coatings
- Oil and grease
- Dust
- Surface laitance
- Existing waterproofing
- Adhesion characteristics
Unsound concrete, loose material and contaminants should be removed.
Cracks and defects should be repaired where required, and the substrate should be brought to the condition specified by the waterproofing manufacturer.
There is specific guidance on substrates for liquid applied waterproofing systems because the condition and compatibility of the substrate are fundamental to system performance.
7. Primers and Reinforcement
Depending on the substrate and waterproofing system, a primer may be required.
The primer can help:
- Improve adhesion
- Stabilise the substrate
- Reduce absorption
- Promote compatibility
- Improve bond strength
Reinforcement may also be incorporated into the waterproofing system.
Reinforcement is particularly useful around areas subject to movement, cracking or complex detailing.
It may consist of materials such as:
- Polyester fleece
- Glass fibre
- Reinforcing mat
- Localised reinforcement
The requirement for reinforcement should be established from the manufacturer's tested system specification rather than assumed for every application.
8. Movement and Crack Bridging
Commercial buildings and car parks are subject to thermal movement, structural movement, shrinkage and vibration.
Waterproofing systems must therefore be capable of accommodating the anticipated movement of the substrate.
Liquid applied membranes can provide flexibility and, where specifically designed and tested for the application, can bridge certain cracks and joints.
Crack and joint-bridging capability is one of the benefits of appropriate liquid applied systems.
However, liquid waterproofing should not be used to conceal significant structural movement.
Active structural cracks, failed movement joints or structural defects should be investigated and appropriately repaired before the waterproofing system is installed.
9. Roofs and Commercial Buildings
Liquid applied waterproofing is particularly suitable for refurbishment of existing commercial roofs where removal of the existing waterproofing may be undesirable or disruptive.
Subject to survey and compatibility testing, some systems can be installed over existing waterproofing.
Potential advantages include:
- Reduced removal of existing materials
- Less disruption
- Lightweight construction
- Seamless detailing
- Ability to follow existing roof geometry
- Simplified treatment of difficult details
- Extended service life of suitable existing roof systems
Many liquid membranes can be used as overlay systems on existing flat roofs and profiled sheet systems.
However, an overlay should only be undertaken where the existing substrate and construction are suitable. Defective or waterlogged roof build-ups may require more extensive intervention.
10. Waterproofing Around Details
Many waterproofing failures occur at details rather than within the main field area.
Particular attention should therefore be given to:
Roof Outlets
The membrane must form a secure and waterproof connection around outlets to prevent water bypass.
Upstands
The waterproofing should be correctly terminated at parapets, kerbs and walls.
Penetrations
Pipes, ducts, cables and other penetrations require properly designed flexible detailing.
Movement Joints
Movement joints must remain capable of moving and should not be rigidly bridged.
Thresholds
Door and access thresholds require careful detailing to prevent water entering occupied areas.
Plant Supports
Plant and equipment should be supported without compromising the waterproofing membrane.
Correct detailing at these locations is essential to achieving a durable waterproof envelope.
11. Installation Requirements
Liquid waterproofing should be installed by appropriately trained and competent applicators.
Installation should consider:
- Ambient temperature
- Substrate temperature
- Humidity
- Rain
- Condensation
- Substrate moisture
- Mixing ratios
- Pot life
- Application rate
- Wet and dry film thickness
- Recoat intervals
- Curing conditions
The manufacturer's installation instructions should be followed precisely.
Inadequate coverage, incorrect mixing or poor substrate preparation can result in premature failure.
Appropriate training and manufacturer support is recommended for the application of liquid waterproofing systems.
12. Quality Control and Inspection
Quality control should be incorporated throughout the installation.
Inspection should include:
- Substrate preparation
- Primer application
- Reinforcement installation
- Material batch numbers
- Application rates
- Film thickness
- Detailing
- Terminations
- Curing
- Surface finish
- Defects
- Final waterproofing integrity
Where appropriate, additional testing can be undertaken to verify the integrity of the completed membrane.
Electronic integrity testing may also be appropriate for certain liquid-applied systems, subject to system compatibility and the testing requirements.
There are specific guidance on electronic integrity testing of liquid applied membranes.
13. How Liquid Waterproofing Helps Protect Reinforced Concrete
The waterproofing system provides a barrier against water and potentially harmful contaminants.
This is particularly important where the substrate is reinforced concrete.
By reducing water and contaminant penetration, the waterproofing system can help reduce the environmental conditions that contribute to reinforcement corrosion.
This can help protect:
- Concrete cover
- Reinforcement
- Beams
- Slabs
- Columns
- Decks
- Ramps
- Structural interfaces
The waterproofing system is therefore not simply a surface finish. It can form an important part of the building's overall durability strategy.
It should, however, be recognised that waterproofing cannot reverse existing reinforcement corrosion or structural deterioration. Existing defects should be assessed and repaired before the waterproofing system is installed.
14. Benefits of Liquid Waterproofing
Seamless Protection
Liquid systems can form a continuous membrane with reduced reliance on conventional sheet laps.
Flexible Performance
Many systems are designed to accommodate thermal and limited substrate movement.
Complex Detailing
Liquid materials can be applied around complicated roof and structural details.
Refurbishment
Suitable systems can often be used to refurbish existing waterproofing without complete removal.
Reduced Disruption
Cold-applied systems can avoid some of the disruption and hazards associated with hot works, depending on the selected product.
Durability
Appropriately selected systems can provide long-term protection against environmental exposure.
Trafficable Applications
Specialist systems can provide hard-wearing and slip-resistant surfaces for balconies, walkways and car parks.
UV Resistance
Some systems provide high resistance to UV exposure, which is important for exposed roofs and decks.
Crack Bridging
Certain systems can bridge specified cracks and joints where designed and tested for that purpose.
Seamless construction, flexibility, durability, UV resistance and crack/joint-bridging capability are among the potential benefits of liquid systems.
15. Maintenance
Liquid waterproofing should be included within the building's planned preventative maintenance programme.
Regular inspections should check for:
- Cracking
- Blistering
- Peeling
- Delamination
- Mechanical damage
- Excessive wear
- Failed details
- Blocked outlets
- Ponding
- Damaged joints
- Deteriorated sealants
- Surface contamination
In multi-storey car parks, additional attention should be given to areas subjected to heavy traffic, braking, turning and repeated wetting.
Drainage systems should also be kept clear because even a high-performance waterproofing system can be adversely affected by persistent ponding and poor drainage.
16. Refurbishment Considerations
Before specifying liquid waterproofing to an existing commercial building or car park, a condition survey should be undertaken.
The survey should establish:
- Existing waterproofing type.
- Substrate condition.
- Moisture condition.
- Existing cracks.
- Movement joints.
- Drainage performance.
- Existing leaks.
- Previous repairs.
- Contamination.
- Compatibility with the proposed system.
Where necessary, adhesion testing and moisture investigations should be completed.
The existing substrate should not simply be coated without understanding its condition.
Where the underlying structure has significant deterioration, the waterproofing should form part of a wider repair strategy rather than being used as a standalone treatment.
17. Why Liquid Waterproofing Is Important
Liquid applied waterproofing provides an important protective layer between the building structure and the external environment.
For commercial buildings, it can help protect roofs, podiums, balconies and other exposed areas from water penetration.
For multi-storey car parks, it can provide additional protection against water, chlorides, chemicals, UV radiation and traffic-related exposure.
By controlling water penetration, a suitable waterproofing system can help reduce the risk of concrete deterioration and reinforcement corrosion.
This can result in:
- Longer structural service life
- Reduced maintenance
- Fewer water leaks
- Reduced repair requirements
- Improved building appearance
- Reduced disruption
- Better asset protection
- Improved durability
18. Conclusion
Liquid applied waterproofing is a versatile and effective method of protecting commercial buildings, roofs, podiums, balconies and multi-storey car parks from water penetration and environmental exposure.
It is applied in liquid form and cures to create a continuous waterproof membrane. The technology includes several different chemistries, each providing different performance characteristics and requiring selection according to the specific application.
Its importance is particularly clear in multi-storey car parks, where exposure to water, chlorides, de-icing salts, vehicle traffic and UV radiation can create aggressive conditions for reinforced concrete. Liquid-applied membranes as a regular waterproofing solution for car parks because they can provide tough, elastomeric and seamless protection.
The success of a liquid waterproofing system depends on appropriate specification, substrate preparation, detailing, application, quality control and maintenance. Particular attention must be given to movement joints, outlets, penetrations, upstands, thresholds and other areas where waterproofing failures commonly occur.
When correctly selected and installed, liquid waterproofing helps prevent water ingress, protect reinforced-concrete structures, reduce deterioration and extend the serviceable life of the building.
For commercial buildings and multi-storey car parks, liquid waterproofing should therefore be considered not simply as a waterproof coating, but as an important component of the overall building protection, durability and asset-management strategy.