Plastics and Rubbers in Building

Topics Covered

Background

Pipes and Gutters

Push-Fit Plastic Piping

Disadvantages of Plastic Piping

Polybutylene

Crosslinked Polyethylene

Electrofusion

Roofing Systems

Cladding Panels

Rubber Anti-Vibration Mounts

Sound Insulation

Thermal Insulation

Window Frames

Background

The use of rubber and plastics materials in buildings, both for construction and decoration, continues to increase, particularly as architects, designers and builders appreciate their advantages in construction terms and in the provision of so called ‘maintenance free’ structures. Today, plastics materials are so widely used in the building industry that it would be difficult to envisage the construction of any building without them. Many products are available which meet the various building and fire regulations. Some of the areas in which these materials are used are listed in table 1.

Table 1. Application of plastics and rubbers in building

Adhesives

Sealants

Roofing materials

Waterproof membranes

Floor coverings

Sound insulation

Thermal insulation

Anti-vibration mountings

Window frames

Glazing

Pipes and gutters

Drainage systems

Fascia boards

Cladding panels

Decorative laminates

Geotextiles for earthworks

Laminates for formwork

Laminates for decoration

Flexible foams for upholstery

Fibres for carpets and fabrics

Paints and varnishes

Pipes and Gutters

For many years we have seen the gradual replacement of traditional materials such as lead, copper, steel, cast iron and ceramic waste systems with plastic pipes and fittings. Some of the advantages gained are a reduction in weight, ease of fabrication and installation, ease of repair and in many cases a reduction in cost. Because plastic pipes have a smoother bore than their metal counterparts, flow rates can be increased and scale formation is reduced. Plastic pipes also offer advantages in corrosion resistance.

Push-Fit Plastic Piping

Within buildings the push-fit waste systems have made plumbing much quicker, and also safer from fire hazards, since blow lamps are no longer necessary to wipe lead joints. Externally, a wide range of soil pipes and fittings are available to carry waste to the main sewers. Here the advantages of lighter weight, longer pipe lengths without joints and ease of fabrication have made these an absolute boon to the industry. Whilst the bulk of the materials used are thermoplastics, such as PVC (polyvinyl chloride), ABS (acrylonitrile butadiene styrene terpolymer) and polypropylene, without the use of rubber O-rings and compression gaskets push-fit systems would be impractical.

With potable water distribution, polyethylene pipes are now widely used. Pipes are available in diameters from a nominal 8 mm bore up to 1000 mm and above, made from specially developed grades of MDPE (medium density polyethylene) which meet a range of water industry specifications (WIS standards). For underground potable water distribution pipes are coloured blue. This enables the contents of a buried pipe to be immediately identified on a construction site. Above ground black coloured polyethylene is used to ensure adequate UV stability. One advantage of plastic pipes over more traditional materials is that in the smaller diameter sizes they are available in continuous lengths of up to 100m or even 250m in some cases. This reduces the number of joints needed and hence the number of potential leaks.

Disadvantages of Plastic Piping

One disadvantage of plastics materials is their tendency to soften at elevated temperatures. This has restricted their use in hot water systems. However, two materials have found application in underfloor heating systems and to a limited extent for hot water distribution. These are polybutylene (PB) and crosslinked polyethylene (PEX).

Polybutylene

Polybutylene can be used in systems with a continuous operating temperature of 82°C and will survive short peak temperatures of up to about 110°C but does require continuous support at these higher temperatures. With underfloor heating systems continuous support presents no particular problem. Pipes are available which meet the requirements of BS 7291: Part 1 Class H, Part 2: 1990 and BS 5955: Part 8, 1990. Although failures have occurred in the USA where high levels of chlorine are present in the water supply, similar problems have not arisen in the UK and Europe where the chlorine content is lower.

Crosslinked Polyethylene

Crosslinked polyethylene (PEX) is made from normal polyethylene by, for example, crosslinking it using a peroxide catalyst. This produces a material which can no longer be processed in the same way as a conventional thermoplastic but which has improved creep resistance and elevated temperature performance. It is finding application in domestic hot and cold water and underfloor heating systems and can withstand operating temperatures of up to about 90°C, with surges to about 110°C. Since these materials are available in coiled lengths of 100 m or more, joints and hence leaks can be minimised, particularly where a central distribution point is used in a similar way to a fuse box in an electrical system.

Yellow coloured polyethylene pipes are now used for gas distribution, particularly where existing domestic supply pipes have corroded. In this case the replacement plastic pipe is threaded through the existing pipe. This overcomes the need for a trench to be excavated and considerably reduces the cost of replacement. Because the pipe bore is smoother the gas flow is hardly reduced.

Electrofusion

One recent innovation in jointing pipes has been the introduction of the electrofusion technique. Here special couplers are available which incorporate a heating coil. The coupler is clamped in . position over the two pipe sections to be joined and power is supplied to the heating coil by means of an electronic control unit. The pipe and coupler melt at the interface between the two materials and a permanent fusion bond is formed. This enables consistent joints to be made using relatively unskilled operatives. Using these couplers, permanent repairs can be made to buried pipes with minimal excavation, since only the damaged part of the pipe needs to be replaced rather than a complete section.

Plastic guttering and drainage pipes can be found on most buildings today, and usage is such that these products are taken for granted in the same way as bricks, concrete and timber are in building construction.

Roofing Systems

Wired glass and corrugated plastic sheeting has been used for roofing in conservatories and buildings where transparent panels have been required. However, in more recent times double and triple walled polycarbonate sheeting has become increasingly used, since this provides not only diffuse daylight for illumination but also heat insulation and hence reduced heating costs.

Twin or triple walled polycarbonate provides a number of advantages during installation since it can be cut with conventional tools, is rigid to handle, does not require closely spaced supports, is light in weight and can be easily fitted. In addition, it can be cold formed or thermoformed into a variety of shapes to provide attractive and functional curved surfaces. Edges and joints can be sealed to prevent draughts. Another major advantage is its resistance to breakage.

Polycarbonate sheeting is available which meets BS 476: Part 7: Class 1 for surface spread of flame. This has enabled the material to be used in public areas of buildings where strict fire regulations apply. Specially UV stabilised grades of polycarbonate are used, often with an additional UV barrier film incorporated under the outer skins. Fixing is usually by means of aluminium or UPVC (unplasticated PVC) glazing bars. However, unlike glass, holes can be drilled through the material for screw fixings. More recently, similar twin walled sheeting made from clear UV stabilised PVC has become available. Both materials, polycarbonate and PVC, are available in clear and bronze colours.

Cladding Panels

UPVC products are now frequently used in place of the more traditional timber products for external cladding panels, fascia and soft boards, particularly on new buildings. Some of the advantages offered by UPVC are lighter weight, resistance to rot, lack of warp and lack' of need for regular maintenance painting. In addition, UPVC meets BS 476: Part 7: Class 1' for surface spread of flame. Products are available in a variety of colours, including wood grain finishes. These may be of solid UPVC, double skin or foam filled double skin construction.

With the double skin cellular construction, sink or shrinkage marks are often seen running along the ribs. Whilst this presents no particular problem with white coloured products, these marks can be unsightly on dark colours.

When fixing UPVC products, unlike their timber counterparts, due allowance must be made for expansion and contraction to prevent buckling of the sheets due to the heating effect of sunlight. Normally an allowance of 2 mm per metre length must be provided between sections. To allow for this special UPVC jointing and corner sections are available.

Rubber Anti‑Vibration Mounts

In many buildings there is a need to prevent external vibrations from affecting sensitive equipment within the building. This necessitates the incorporation of anti-vibration mounts during the construction of the building. In the UK, laminated elastomeric bearings are usually chosen but in France and Germany, steel coil springs are more often used. Although rubber vibration isolating systems have been known for many years, it is only in the last 10 years or so that methods have become available for designing and analysing high efficiency compound systems.

Rubber springs tend to be less massive than the equivalent steel springs for any particular application. In addition, the dynamic properties of rubber can result in such mounts providing protection over a wider range of frequencies, particularly at high frequencies.

Rubber mounts are also used to isolate individual items of equipment, such as air conditioning and refrigeration equipment, from the main structure of the building.

Sound Insulation

Sound within buildings may be general noise transmitted through walls and floors or a specific noise from vibrating machinery. The latter can be dealt with by using vibration mounts as mentioned above. Air-borne noise can also present problems and must be taken into account when designing sound insulation systems.

With general noise, the traditional method was to build very thick and heavy walls and floors. However, as buildings have become lighter, other methods of sound reduction have become necessary. As a general principle, sound insulation can be provided by either a simple and heavy or a light and complex construction. It is in this latter area that rubber and plastics materials have come to the fore.

The performance of party walls and floor is controlled by the Building Regulations which give typical constructions that meet the performance requirements. To meet the regulations with light weight constructions some form of dry lining, floating floor or suspended ceiling is needed. However, in all these cases the method of fixing can reduce the efficiency of the system.

With floating floor construction, an air gap, created by placing a resilient material such as rubber or foamed plastic between the timber raft and the concrete floor, can achieve the desired result. Since the demand for fight weight constructions is increasing, this will provide a steadily increasing outlet for rubber and foamed plastics.

With walls in housing, dry lining is often used but in offices and factories, composite wall panels incorporating foamed plastics are available that are easily installed and that provide adequate sound insulation.

Thermal Insulation

As well as sound insulation, buildings need thermal insulation. This can be met by using light weight aerated concrete building blocks during the construction of the building or by incorporating foamed plastic sheeting within the structure. Typical foamed plastics include rigid polyurethane foam and expanded polystyrene, although various other foamed plastics may also be used.

Plasterboard can be readily obtained with a 25 mm foamed polystyrene backing. Other composite sheet building products can be obtained with polyurethane foam cores. One particularly important use of polyurethane foams is in the construction of cold rooms for food storage. Here a 100 mm thick sheet of polyurethane foam is sandwiched between two layers of glass fibre reinforced polyester (GRP) or two layers of sheet steel. The surface of the GRP can be flat or lightly embossed to give a semi-decorative appearance. Such surfaces are ideal for use in food storage areas since they can be kept clean with very little effort.

For all these applications, whether for sound or thermal insulation, fire retardant foams are available which meet the appropriate building and fire regulations.

Window Frames

UPVC has been in use for many years for the manufacture of window frames and in particular, frames used for double glazed windows. These comply with BS 5720. One of the major advantages is the reduced thermal conductivity over equivalent metal frames. This in turn reduces condensation on the frame. UPVC frames can be easily assembled and do not require regular maintenance. Neither do they need a wooden surround or sub-frame, which can rot. Frames come complete with window as well as other parts of the frame and surround, all manufactured from the same grade of white UPVC. With larger frames, steel reinforcement is often added for extra strength and security.

A water tight seal to concrete and brickwork is achieved by bedding the frame in silicone rubber and by injecting a silicone rubber bead along all joints.

 

Primary author: R.G. Weatherhead

Source: Materials World Vol. 1 no. 2 pp. 95-97 February 1993

 

For more information on this source please visit The Institute of Materials.

 

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