LDPE Liner Application in Building Construction

For a building construction project in Siwan, Bihar, Ocean Non Wovens supplied 22,145 kg of Ocean LDPE Liner 125 Micron. The liner was laid as a barrier beneath foundation and flooring elements to stop ground moisture reaching the concrete.

Project overview

• Project name: Building Construction Project
• Location: Siwan, Bihar
• Product used: Ocean LDPE Liner, 125 Micron
• Quantity: 22,145 kg

Why the slab needed a barrier

Reinforced cement concrete (RCC) carries the structural load, but it is porous. Water rising from the ground can move through a slab, leaving damp floors, damaging floor finishes and, over time, corroding reinforcement. Siwan sits on the fine-grained alluvial soils of the Gangetic plain, where this is a common problem.

The geomembrane layer was installed to act as a vapour barrier, block water migrating up from the subgrade and protect the long-term performance of the structure.

What an LDPE liner does under a building

LDPE (low-density polyethylene) sheet is flexible, chemically resistant and practically impermeable to liquid water. Under a building it does several jobs:

• Vapour barrier: stops moisture moving upward from the soil into concrete slabs.
• Separation layer: keeps soil from mixing into the blinding or slab concrete.
• Waterproofing support: adds a continuous membrane below the concrete and flooring system.
• Temporary containment: used in curing zones and as a protection layer during construction.

A sheet laid on the subgrade before concreting also stops dry soil from drawing water and cement paste out of the fresh concrete, which helps the bottom of the slab cure properly. LDPE suits low-load applications like this, where flexibility and quick installation matter more than the puncture resistance of a thick HDPE sheet.

Site conditions in Siwan

• Alluvial soil: fine-grained soils with high moisture retention, low shear strength and a tendency to settle.
• Capillary rise: fine soils draw groundwater upward continuously, causing damp floors, weaker concrete and a higher risk of reinforcement corrosion.
• Monsoon: heavy rain saturates the subgrade, causes temporary waterlogging and lowers bearing capacity.

The LDPE liner works as a capillary break: water can rise through the soil up to the sheet, but not past it into the structure.

Installation and quality control

A thin membrane only works if it stays continuous. On smaller building jobs installation is often rushed, so these steps matter:

• Subgrade preparation: remove sharp objects, debris and organic matter; grade and compact to a smooth, even surface.
• Placement: unroll carefully to avoid wrinkles and folds, keep sheets aligned and leave enough overlap between them.
• Jointing: seal overlaps so they do not become seepage paths, using adhesive tape or heat sealing depending on site conditions.
• Protection: keep reinforcement bars, spacers and equipment from tearing the sheet, and add a protective layer where needed. Patch any tear before concrete is poured.

A single open overlap or puncture gives moisture a path around the whole barrier.

Long-term performance

LDPE liners are thinner than HDPE geomembranes, but in a buried, low-stress application like this they do the job well:

• Impermeability: keeps water out of structural layers.
• Flexibility: follows minor subgrade movement without cracking.
• Chemical resistance: unaffected by the mild contaminants found in ordinary soils.
• Thermal stability: performs through normal temperature variation.

Once buried under concrete, the liner is protected from UV and mechanical damage, which are the main causes of polyethylene degradation, so it can keep working for a long period.

Maintenance benefits

• Fewer damp patches and moisture-related defects
• Lower repair costs for flooring and foundations
• Drier, healthier indoor conditions
• Longer service life for the structure

An under-slab barrier is cheap to lay during construction and very hard to add later, which is why it belongs in the foundation design on sites with alluvial soil and high moisture like Siwan.

Ocean Non Wovens

Ocean Non Wovens supplies geomembranes, geotextiles and other geosynthetics for building and infrastructure projects across India, with support on material selection for local site conditions. See more projects in our case studies, or read about geosynthetics and their use in landfills and containment.