Plastics and Rubbers in Buildings

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Article updated on 02/03/20 by Clare Kiernan

The use of rubber and plastic materials in buildings, both for construction and decoration, continues to increase, particularly as architects, designers and builders appreciate their advantages in construction terms and the provision of ‘maintenance-free’ structures. Today, plastic materials are so widely used in the building industry that it would be difficult to envisage the construction of any building without them. Notably, many plastic 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 Anti-vibration mountings Decorative laminates
Sealants Window frames Geotextiles for earthworks
Roofing materials Glazing Laminates for formwork
Waterproof membranes Pipes and gutters Laminates for decoration
Floor coverings Drainage systems Flexible foams for upholstery
Sound insulation Fascia boards Fibres for carpets and fabrics
Thermal insulation Cladding panels 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 and costs, as well as improved ease of fabrication, installation and repair. Because plastic pipes have a smoother bore as compared to their metal counterparts, flow rates can increase while scale formation is reduced. Plastic pipes also offer advantages in corrosion resistance.

Push-Fit Plastic Piping

Within buildings, 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, in combination with an ease of fabrication, have made these an absolute boon to the industry. Whilst the bulk of the materials used are thermoplastics, such as polyvinyl chloride (PVC), acrylonitrile butadiene styrene terpolymer (ABST) 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. These pipes are available in diameters ranging from a nominal 8 millimeters (mm) up to 1000 mm. Furthermore, polyethylene pipes are made from specially developed grades of medium density polyethylene (MDPE), which meets a range of water industry specification (WIS) standards.

For underground potable water, distribution pipes are colored blue, which enables the contents of a buried pipe to be immediately identified on a construction site. Above ground, black colored polyethylene is used to ensure adequate UV stability. One advantage of plastic pipes as compared to more traditional materials is that, in the smaller diameter sizes, they are available in continuous lengths of up to 100 meters (m), or even 250 m in some cases. This reduces the number of joints needed and hence the number of potential leaks.

Disadvantages of Plastic Piping

One disadvantage associated with plastic materials is their tendency to soften at elevated temperatures, which has restricted their use in hot water systems. However, two materials that have found application in underfloor heating systems and to a limited extent for hot water distribution include polybutylene (PB) and cross-linked polyethylene (PEX).

Polybutylene

PB 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; however, this material does require continuous support at these higher temperatures. With underfloor heating systems, continuous support presents no particular problem.

PB pipes are available to 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 United States, 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.

Cross-linked Polyethylene

PEX is made from normal polyethylene that has been crosslinked by a peroxide catalyst. This linkage produces a material which can no longer be processed in the same way as a conventional thermoplastic, but instead has improved creep resistance and elevated temperature performance. PEX pipes can be found in domestic hot and cold-water systems, as well as underfloor heating systems. Notably, PEX pipes 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, subsequently, leaks can be minimized, particularly where a central distribution point is used in a similar way to a fuse box in an electrical system.

Yellow colored 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. As the pipe bore is smoother, the gas flow is hardly reduced.

Electrofusion

One innovation in jointing pipes has been the introduction of the electrofusion technique, which utilizes special couplers to incorporate a heating coil. The coupler is clamped in and positioned 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, which 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 in most buildings today.

Roofing Systems

Wired glass and corrugated plastic sheeting have been used for roofing in conservatories and buildings where transparent panels have been required. However, further developments have seen the increased use of double and triple walled polycarbonate sheeting, which not only provides diffuse daylight for illumination, but also heat insulation which reduces heating costs.

Twin- or triple-walled polycarbonate materials provide a number of advantages during installation, as they can be cut with conventional tools, are rigid to handle, do not require closely spaced supports, are light in weight and can be easily fitted. In addition, these materials can be cold-formed or thermoformed into a variety of shapes to provide attractive and functional curved surfaces. Other major advantages of these materials include their resistance to breakage, as well as the ability to seal both their edges and joints to prevent draughts.

Polycarbonate sheeting meets BS 476: Part 7: Class 1 for surface spread of flame, which has enabled the material to be used in public areas of buildings where strict fire regulations apply. Specially ultraviolet (UV) stabilized grades of polycarbonate are used, often with an additional UV barrier film incorporated under the outer skins. Fixing is usually achieved through the addition of aluminum or unplasticated PVC (UPVC) 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 stabilized PVC has become available. Both polycarbonate and PVC materials are available in clear and bronze colors.

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 include lighter weight, resistance to rot, as well as a lack of warp and need for regular maintenance painting. In addition, UPVC meets BS 476: Part 7: Class 1 for surface spread of flame, as described above. UPVC materials may be of a solid, 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-colored products, these marks can be unsightly on dark colors.

When fixing UPVC products, unlike their timber counterparts, users should allow for expansion and contraction to occur in order to prevent buckling of the sheets due to the heating effect of sunlight. Normally an allowance of 2 mm/m 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 these methods have become available for designing and analyzing high-efficiency compound systems.

Rubber springs tend to be less massive than the equivalent steel springs in 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 arise from general noise transmitted through walls and floors or be the result of noise generated by vibrating machinery. The latter noise category 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 has been to build very thick, 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 construction, or a light and complex one. It is in this latter area that rubber and plastics materials have come to the fore.

The performance of party walls and floors is controlled by Building Regulations which give typical constructions that meet performance requirements. To meet the regulations on lightweight constructions, some form of dry lining, floating floor or suspended ceiling is needed. However, in each of 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. As the demand for fight weight constructions increases, 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. These materials can be easily installed and provide adequate sound insulation.

Thermal Insulation

In addition to sound insulation, buildings require thermal insulation. This type of insulation can be met by using lightweight 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. Herein, a 100 mm thick sheet of polyurethane foam is sandwiched between two layers of glass fiber 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 each of these applications, whether for sound or thermal insulation, fire retardant foams that meet the appropriate building and fire regulations are available.

Window Frames

UPVC has been in use for many years for the manufacturing of window frames and, in particular, frames used for double glazed windows. Each of these applications of UPVC comply with BS 5720. One of the major advantages of UPVC include its reduced thermal conductivity over equivalent metal frames, which, in turn, reduces condensation on the frame.

UPVC frames can be easily assembled and do not require regular maintenance. Furthermore, UPVC frames do not require a wooden surround or sub-frame, both of which can rot. These unique frames come complete with the window as well as other parts of the frame and surround, all of which are manufactured from the same grade of white UPVC. With larger frames, steel reinforcement is often added for extra strength and security. UPVC frames are also equipped with a water-tight seal to concrete and brickwork, which 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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