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Waterproofing Membranes
Several generic classes of polymeric materials have emerged, all of which are suited to the exposure conditions for roofing. However, because of the nature of the material, each has a different spectrum of properties that the manufacturer can modify, by changing the formulation, reinforcement/carrier (if any) and production process. Even within the same class of materials, manufacturers will adopt different approaches to exploit whichever balance of properties meets general requirements or specific market conditions. In these latter cases, a particular material can, for example, be complimentary to the type of roof construction, the attachment method or the required performance.
The nature of single ply material ensures satisfactory physical properties over a working temperature range of below -30°C to above 80°C, which exceeds all UK environmental conditions including allowance for solar radiation and cooling. Single ply membranes can be jointed by hot air, solvent welding, or adhesive tapes depending upon material type and manufacturers’ preferences.
Polymers suitable for roofing applications are usefully classified according to the extent of cross-linking between the polymer chains, because this determines many of their characteristics and the method of forming seams. These range from thermoplastics to elastomers, with some materials displaying features of both.
Thermoplastic
- Polyvinylchloride (PVC) is made flexible by the addition of plasticisers. PVC can be heat or solvent welded, but is generally not suitable for direct contact with bitumen.
- Chlorinated Polyethylene (CPE) is made flexible by the chlorination process. CPE can be heat or solvent welded and is compatible with bitumen.
- Vinyl ethylene terpolymer (VET) is made flexible by blending Ethylene Vinyl Acetate (EVA) with PVC, with the EVA acting as a plasticiser. VET can be heat or solvent welded and is compatible with bitumen.
- Chlorosulphonated Polyethylene (CSM) is made flexible by the chlorosulphonation process and can be solvent or heat welded. After external exposure, CSM’s properties are modified to produce a partially vulcanised membrane that improves weather resistance, but impairs the weldability. CSM is compatible with bitumen.
- Flexible Polyolefin (FPO) membranes consist of a composition based on internally plasticised polyolefines. FPO’s can only be heat welded.
- Polyisobutylene (PIB) incorporates a high proportion of carbon black to provide good physical properties. PIB products available on the UK market are suitable for solvent welding by tape systems.
Elastomeric
- Ethylene propylene diene monomer (EPDM) is a naturally flexible material to which carbon black is added. Jointing is normally carried out with tape bonding using a special primer, but adhesives can also be used.
© 2006 Sarnafil Ltd. Legal Disclaimer
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