500mu (2000G) Black Polythene Damp Proof Membrane (DPM) 4m x 12.5m (50m2/Roll)

What Is 500mu Polythene DPM?

500mu Polythene Damp Proof Membrane (DPM) is engineered to provide the highest level of defence against the ingress of ground moisture. This super heavy-duty membrane, manufactured from resilient, high-quality low-density polythene (LDPE), achieves its protective capabilities through its substantial nominal thickness of 500 microns (equivalent to 0.50mm or 2000 gauge). 

When correctly installed beneath concrete ground-bearing slabs, its principal function is to establish an unbroken and impermeable barrier. This physical separation is critical in preventing the rise of naturally occurring ground water, a phenomenon commonly referred to as 'rising damp'. 

Its use safeguards the building's foundational elements, flooring structures, and internal habitable environment from the deleterious consequences of persistent dampness, such as material degradation, reduced thermal efficiency, and potential health concerns. 

Understanding Thickness: Microns (µm) and Gauge (G) Explained

• What is a Micron? A micron (symbol: µm) is a very small unit of measurement, equal to one-millionth of a metre. To illustrate, a human hair can be around 50-70 microns thick. Therefore, 500µm means this DPM sheet is an incredibly substantial 0.50 millimetres thick.   
• What is Gauge? Gauge (often abbreviated as 'G') is another way to express the thickness of polythene sheeting. For DPMs, the conversion is typically 1 micron = 4 gauge. Consequently, a 500-micron DPM is equivalent to a formidable 2000 Gauge (500 x 4 = 2000).   
• Why Thickness Matters: The thickness of a DPM is paramount to its performance. A membrane of this extreme 500mu calibre offers: 
  • Unparalleled resistance to tearing, punctures, and impact damage during the installation process, even when faced with the most challenging sub-bases or intensive site activities.
  • An exceptionally robust, highly durable, and virtually impenetrable long-term barrier against moisture, providing the utmost confidence and peace of mind.
• 500µm / 2000 Gauge - What does it mean for your project? This thickness designates a super heavy-duty or extreme-duty DPM. It is the definitive choice for projects requiring the absolute maximum in durability and moisture protection. This includes sites with very poor, aggressive, or contaminated ground conditions (when used as part of an approved gas/contaminant barrier system), areas subject to exceptionally high loadings, or where the most stringent specifications for damp proofing are mandated by architects, engineers, or for critical infrastructure. It provides an unmatched level of resilience against physical damage and moisture ingress.

Applications

• Under Concrete Floors (Ultimate Performance): Installed as a ground-level moisture barrier directly beneath new solid concrete floor slabs. It is essential for industrial facilities, commercial buildings with sensitive environments, high-value residential properties, basements (as part of a comprehensive tanking system compliant with BS 8102), and any construction on challenging or contaminated land where maximum, failsafe protection is demanded.
• Ultimate Heavy-Duty Protection & Containment (Secondary Use): Its exceptional strength and impermeability make it suitable for the most critical temporary protection tasks, as a heavy-duty pond liner (check specific suitability), or for certain containment applications where extreme toughness is required.

Benefits

• Ultimate Moisture Defence: Provides an exceptionally strong, reliable, and enduring barrier against rising damp, ensuring the building's interior remains dry and protected under the most adverse conditions.
• Unparalleled Durability & Resilience: The 500-micron (2000 gauge) polythene offers supreme durability with ultimate resistance to punctures, tears, and abrasion during and after installation. It also robustly resists common ground contaminants and rot.   
• Maximum Integrity from Robust Sheeting: Supplied in a 4m x 12.5m roll (covering 50m²), its extreme thickness ensures each sheet offers maximum inherent strength, contributing to an exceptionally reliable overall barrier.   
• Waterproof & Rot-Proof: Polythene is inherently waterproof and will not rot or decay when buried in the ground, guaranteeing its integrity for the building's lifetime.
• Installation Considerations: Due to its substantial weight and reduced pliability compared to thinner membranes, installation requires careful planning, appropriate manpower, and meticulous attention to detail, especially when forming and sealing joints.
• Exceeds Highest Standards: DPMs of this extreme thickness are manufactured to meet and exceed the most rigorous performance criteria outlined in UK Building Regulations and will typically hold BBA certification and comply with standards like BS EN 13967.

Installation Guidelines

Correct installation is absolutely critical for a high-performance DPM to function effectively. Always consult the current UK Building Regulations (Approved Document C – which deals with site preparation and moisture resistance) and relevant British Standards (like BS 8215 – a code of practice for damp-proof courses) for full details.

• Prepare the Ground (Sub-Base): The ground layer beneath the DPM (compacted hardcore) must be impeccably level and smooth. It is non-negotiable that it is covered with sand blinding (a layer of soft sand, at least 50mm thick, well compacted) to create a uniform, protective cushion, safeguarding even this ultra-thick DPM from potential point loads or sharp elements.
• Laying the DPM: Carefully unroll the DPM over the prepared sand blinding. This will require several operatives due to the significant weight and stiffness of a 500mu roll. Avoid any dragging that could stress the material. Plan the layout to minimise complex cuts or formations where possible.
• Overlapping (Lapping) & Sealing Joints: All adjacent sheets must be overlapped by at least 300mm (in line with current best practice, e.g., NHBC Standards 2025, 5.1.20). These laps must be meticulously cleaned (ensure surfaces are dust-free and dry) and securely sealed using high-performance, compatible double-sided DPM jointing tape between the sheets. The edge of the lap should then be over-sealed with a compatible heavy-duty single-sided DPM lap tape. Apply significant, uniform pressure to all taped joints using a hard roller to ensure a complete, durable, and impermeable seal, as the inherent stiffness and thickness of the material make achieving a perfect bond more challenging and critical.
• Connecting to Wall DPC: The DPM in the floor must be seamlessly and robustly integrated with the Damp Proof Course (DPC) in the surrounding walls. The floor DPM should be carefully detailed and turned up at all perimeter edges and internal load-bearing walls to meet or overlap the wall DPC according to approved, often project-specific, details, forming a continuous and unbroken moisture barrier. Forming neat upstands with this thickness will require care.
• Dealing with Pipes (Service Penetrations): All pipes, cables, or other services passing through the DPM require extremely careful and durable sealing methods. This is typically achieved using proprietary pre-formed top-hat units specifically designed for thick, heavy-duty membranes, or by employing specialised high-bond DPM tapes and/or compatible mastics, ensuring a permanent, robust, watertight seal around each penetration.
• Protect the Membrane: After laying, the DPM must be rigorously protected from any form of damage. Given its role in high-protection scenarios, any puncture, however minor, is a significant concern and must be repaired immediately using a patch of the same DPM material, generously lapped (e.g., at least 150mm, but preferably 300mm for this grade, beyond the damage in all directions) and fully sealed as per jointing instructions, using appropriate primers if recommended for the tapes with this DPM thickness. The DPM should be covered by the subsequent construction layer as soon as practically possible.

Disclaimer: This information is for general guidance only. Always refer to the specific manufacturer's product data sheet, current UK Building Regulations (including Approved Document C), relevant British Standards (such as BS 8215), and other applicable industry guidance (like NHBC Standards) for definitive technical specifications and installation instructions before use. Site conditions and project-specific requirements, especially those mandating a 500mu DPM, must always be taken into full account and professional engineering advice sought where necessary.