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Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Polythene—polyethylene—has several distinct roles in construction: beneath a concrete slab it can limit moisture movement from the ground; in a floor build-up it can act as a moisture barrier or separation layer; and, when supplied as part of a certified system, it can help protect against ground gases. Dimpled HDPE cavity-drain membranes are a related but different technology for managing water below ground. The right choice depends on the assembly, product certification and installation details—not simply on the fact that a material is plastic sheet.
What polythene does in a construction assembly
“Polythene” is polyethylene, but the name alone does not establish what a sheet is suitable for. A membrane’s function depends on its product specification, certification, jointing details and place in the building assembly. A flat sheet under a slab, a sheet separating floor layers and a dimpled drainage membrane are not interchangeable.
Under-slab moisture and vapor control
A polyethylene sheet can be installed beneath a concrete slab to limit moisture moving up from the ground. The U.S. Department of Energy’s Building America Solution Center describes polyethylene sheeting beneath a slab as a capillary break and discusses taped seams (DOE Building America Solution Center guidance).
For a product-specific example, New Zealand’s Ministry of Business, Innovation and Employment CodeMark listing describes SHIELD Polythene Film as a 250-micron film for residential and commercial slab applications. That figure applies to the named product and its certified scope; it is not a universal thickness requirement for under-slab barriers (MBIE CodeMark certificate CMNZ70194).
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Moisture barriers and separation layers in floors
Polyethylene may also serve as a moisture barrier or separation layer within a specified floor build-up. Sika describes Sikaplan-130 PE, a 0.30 mm LDPE sheet, for loose laying beneath ground-supported slabs or between flooring layers, including floating or unbonded screeds. Follow the named product’s instructions and confirm that its use suits the proposed assembly (Sika Sikaplan-130 PE product information).
When a polyethylene system protects against ground gases
Some certified polyethylene systems are designed for more than damp-proofing. The British Board of Agrément certificate for Visqueen Gas Barrier describes an LDPE damp-proof and ground-gas barrier for stated concrete ground-floor applications above or below slabs that are not subject to hydrostatic pressure. Its listed protection includes moisture, radon, methane and carbon dioxide (BBA certificate 13/5069).
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- Packaged plastic sheet has dozens of uses around the home, garden and garage
- Use it to cover and protect furniture, appliances and equipment
- Use to make storm windows and doors and to protect building materials, machinery or other things stored outdoors
- Use as a boat cover, as a moisture barrier; to make temporary enclosures; to cover plants and shrubs, etc.
- Light weight drop cloths are for covering furniture. The heavier weights can be used on the floor to cover carpeting, rugs, hardwood floors, etc.
This certification does not establish that ordinary polyethylene film blocks soil gases. Where gas protection is required, specify the appropriate certified system and obtain qualified design advice for the site and assembly.
Below-grade drainage: a different membrane approach
Dimpled HDPE cavity-drain membranes manage water through a designed drainage system; they do not perform the same role as a flat sheet beneath a slab. Delta describes Delta PT as a damp-proofing base and water-control or drainage membrane for uses including tunnel construction and remedial basement waterproofing (Delta PT). Delta MS 20 is described as an HDPE cavity-drain membrane for water control and management in building and civil-engineering construction (Delta MS 20).
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- MULTI-PURPOSE: this durable, construction-grade polyethylene sheeting provides protection against water vapor and foreign matter
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- WE’VE GOT YOU COVERED: Rolls come in a variety of lengths and widths for small and large-scale projects
- CLEAR FILM: This product contains recycled materials, causing the clear film to be opaque
These products are examples of a related membrane technology, not universal basement solutions. Their suitability depends on the system design and installation, including how collected water is managed.
Specify and install the membrane as a system
Start with the project assembly, applicable local code requirements, the product certificate and the manufacturer’s current instructions. Check that the product’s stated function and certification match the intended use. Do not choose thickness or overlap from a generic rule of thumb.
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- 6Mil Clear Plastic Sheeting: Engineered from 100% new industrial-grade Low Density Polyethylene (LDPE), this heavy-duty plastic sheeting offers exceptional toughness and tear resistance for demanding protection.
- UV Defense (>20%): Our greenhouse plastic covering features built-in UV blockers that shield plants by filtering out over 20%of harmful rays, preventing film degradation.
- Plastic Sheeting Light Diffusion (>90%): Transmitting over 90%natural light, this clear plastic sheeting diffuses sunlight evenly across plants for balanced greenhouse growth and minimized hot spots.
- All-Weather Protection: Built to with stand punishing elements like wind, rain, hail, and snow, this rugged plastic covering delivers reliable protection season after season.
- Versatile for Greenhouses and Gardens: This plastic film is ideal for outdoor applications such as greenhouse plastic film, garden seedbeds, plant protection or moisture barrier, paint splash protector, and furniture/equipment covering.
Prepare and protect the sheet
- Check the substrate and keep sharp objects and construction traffic from damaging the membrane.
- For SHIELD Polythene Film, the CodeMark certificate calls for inspecting for holes and tears before concrete placement and repairing defects. It also warns against puncturing the sheet when placing reinforcement (MBIE CodeMark certificate CMNZ70194).
- Protect the product from sunlight and storage damage as directed. SHIELD’s certificate limits sunlight exposure to 30 days; Sika says to cover Sikaplan-130 PE promptly to avoid UV degradation. These limits apply to the named products, not to all polyethylene sheets (MBIE CodeMark certificate; Sika product information).
Follow product-specific laps and repairs
Joint details differ by product. SHIELD’s certificate specifies laps of at least 150 mm before taping. Sika specifies a 50–100 mm minimum overlap for Sikaplan-130 PE. These figures demonstrate why one product’s installation detail should not be applied to another (MBIE CodeMark certificate; Sika product information).
Use compatible materials and the repair method approved for the selected membrane. For SHIELD, the certificate specifies patching holes or tears with 50 mm PVC tape. At edges, penetrations and transitions, use the designed system details: a generic lap alone does not establish a waterproof junction (MBIE CodeMark certificate CMNZ70194).
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- Plastic Sheeting has dozens of uses around the home, garden and garage
- Use it to cover and protect furniture, appliances and equipment and/or to make storm windows and doors
- Use to protect building materials, machinery or other things stored outdoors
- Use as a boat cover, as a moisture barrier, to make temporary enclosures, to cover plants and shrubs - the possibilities are endless
How to compare options for a project
Compare products by intended function and the demands of the full assembly, rather than treating every membrane as a substitute for every other one.
- Function: Is the requirement moisture control beneath a slab, separation within a floor, certified ground-gas protection, or drainage below grade?
- Certification and jurisdiction: Does the certificate cover the proposed application and location?
- Product specification: What material and thickness does the manufacturer state for the named product?
- Installation: What lap, jointing, repair and penetration details are specified?
- Compatibility and exposure: Does the membrane work with the surrounding materials, and what protection or exposure limits apply?
- System design: For below-grade drainage or gas protection, are the required transitions and supporting system details addressed?
For general moisture-control context, the U.S. Environmental Protection Agency’s Moisture Control Guidance for Building Design, Construction and Maintenance discusses moisture management as a building-design and construction issue.
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