JOINING PLASTIC PIPING

Most waste pipes installed today are made of plastic, which is cheap, lightweight and easy to work with.

A little practice and careful measuring will enable you to replace all parts of your system.

Here’s how to join them together.

THE TOOLS YOU’LL NEED.

– hacksaw – a junior or larger – for cutting the lengths of pipe as you need them

– piece of paper – to help cut the pipe truly square

– tape measure.

– file – for chamfering the pipe ends.

– fine glasspaper – to abrade pipes and sockets for solvent-welding, and for cleaning up the ends of pipes where you have cut them.

– pencil – for marking the cutting points and socket depths to find the working area of the pipe.

VITAL ACCESSORIES.

– solvent cement – for solvent-welding.

– cleaning fluid – for cleaning the pipe ends and socket fittings when making solvent-weld joints.

– petroleum jelly – for lubrication when inserting the pipe into the socket in push-fit joint assemblies.

– tissues or rag for cleaning off excess solvent or petroleum jelly.

TYPES OF PIPE

Unplasticised PVC (UPVC) is used for all waste pipe applications.

Modified PVC (MPVC) has rubber or some other plasticiser added to make it more resistant to shock.

Chlorinated PVC (CPVC or MUPVC) is used where very hot water discharge occurs, such as washing machine out-flows.

Polypropylene is an alternative to

PVC and can withstand hot water – but it expands a lot and is only suitable on short runs.

Acrylonitrile butadiene styrene (ABS) is stronger than UPVC and is used for waste connection mouldings.

SAFETY TIPS.

– don’t smoke when you are solvent-weld jointing – solvent cement and solvent cement cleaner become poisonous when combined with cigarette smoke.

– don’t inhale the fumes of solvent-weld cement or cleaning fluid – so avoid working in confined spaces.

– don’t get solvent-weld cement on any part of the pipe you’re not joining as this can later lead to cracking and weaknesses, especially inside sockets where the solvent cement can easily trickle down.

– hold all solvent-weld joints for 15 seconds after joining and then leave them undisturbed for at least 5 minutes – if hot water is going to flow through the pipe don’t use it for 24 hours.

Waste systems draining baths, basins and sinks used to be made of lead, heavy galvanised steel with screwed joints, or copper. Soil pipes from Wcs were traditionally cast iron, as was all the outside pipework for both waste and soil disposal. Nowadays waste and soil pipes are made of one or other of a variety of plastic materials, which may be used for repairs, extension work or complete replacement of an existing system.

These plastic pipes are lightweight and easily cut, handled and joined. They are made of materials usually known by the initials of their chemical names – UPVC (unplasticised polyvinyl chloride), MPVC (modified polyvinyl chloride), ABS (acry-lonitrile butadiene styrene) and PP (polypropylene). CPVC (chlorinated polyvinyl chloride) is usually used for hot and cold water supply pipes. Pipes and fittings are available in white, grey or a copper colour, depending on type and manufacture.

All these materials are satisfactory for domestic waste systems and – with one exception – can all be joined in the same way: either by push-fit (ring-seal) jointing or by solvent welding.

The exception is PP pipe. This was first developed because of its good resistance to very hot water and chemical wastes, and was therefore extensively used in industry. Nowadays, however, it is frequently used in the home for waste or rainwater drainage. The big difference between PP and other plastic pipes used in waste drainage is that it cannot be solvent-welded. All joints must be push-fit. In most situations this is no great disadvantage but it does make it important to be able to distinguish PP from other plastics. It has a slightly greasy feel and, when cut with a fine toothed saw, leaves fine strands of fibrous material round the cut edges.

Sizes

When buying plastic pipe and components it is wise to stick to one brand only. Pipes and fittings from different makers, though of the same size, are not necessarily interchangeable. Most suppliers stock the systems of only one manufacturer, although the same manufacturer may make both PP and either PVC or ABS systems.

It is worth asking the supplier if there is an instruction leaflet supplied by the maker. There are slight variations in the methods of using each particular make of pipe and fitting. The manufacturer’s instructions, if available, should be letter.

Buying new pipe

Existing waste pipe is likely to be imperial in size – 1 1/2in internal diameter for a sink or bath and 11Ain internal diameter for a wash basin.

Metric sized plastic pipes are normally described – like thin-walled copper tubes -by their external diameter, though at least one well-known manufacturer adds to the confusion by using the internal diameter. Both internal and external diameters may vary slightly – usually by less than one millimetre between makes. This is yet another reason for sticking to one make of pipe for any single project.

The outside diameter of a plastic tube that is the equivalent of a 1 1/iin imperial sized metal tube is likely to be 36mm and the inside diameter 32mm. The outside diameter of the equivalent of a 1 1/2in pipe is likely to be 43mm and the inside diameter 39mm. If in doubt, it is usually sufficient to ask the supplier for waste pipe fittings for a basin waste or – as the case may be – a bath or sink waste. Plain-ended plastic pipe is usually supplied in 3m (10ft) lengths, though a supplier will probably cut you off a shorter piece.

Joining solvent-weld types

Solvent-weld fittings are neater and less obtrusive than push-fit ones and they offer the facility of pre-fabrication before installation. However, making them does demand a little more skill and care and – unlike push-fit joints – they cannot accommodate the expansion (thermal movement) that takes place as hot wastes run through the pipe. A 4m length of PVC pipe will expand by about 13mm (just over Vsin) when its temperature is raised above 20°C (70°F). For this reason, where a straight length of waste pipe exceeds 1.8m (6ft) in length, expansion couplings must be introduced at 1.8m intervals if other joints are to be solvent-welded. This rarely occurs in domestic design, however, and use of push-fit or solvent-weld is a matter of personal preference.

Although the instructions given by the different manufacturers vary slightly, the steps to making solvent-weld joints follow very similar lines. Of course, the first rule is to measure up all your pipe lengths carefully. Remember to allow for the end of the pipe overlapping the joint. When you’ve worked out pipe lengths cutting can start.

Cut the pipe clean and square with a hacksaw or other fine-toothed saw. A useful tip to ensure a square cut is to fold a piece of newspaper over the pipe and join the edges beneath it. The paper will then act as a template.

Remove all internal and external ‘burr’ or roughness at the end of the pipe, then use a file to chamfer the outside of the pipe end to about 45°. Not all manufacturers recommend this, but it does provide an extra key for the solvent.

Insert the pipe end into the fitting and mark the depth of insertion with a pencil. Using medium grade abrasive paper, or a light file, 2 – lightly roughen the end of the pipe, as far as the pencil mark, and also roughen the interior of the socket. Thoroughly clean the roughened surfaces of the socket and the pipe end using a clean rag moistened with a spirit cleaner recommended by the manu-facturer of the fittings.

Select the correct solvent cement (PVC pipes need a different solvent cement from ABS ones; once again, buy all the materials needed at the same time from the same supplier). Read the label on the tin and stir only if instructed.

Using a clean paintbrush apply the solvent cement to the pipe end and to the inside of the fittings, brushing in the direction of the pipe. It is usually necessary to apply two coats to ABS pipes and fittings. The second coat should be brushed on quickly before the first has dried.

Push the pipe fully home into the fitting (some, but not all, manufacturers suggest that this should be done with a slight twisting action). Remove excess solvent cement and hold the assembled joint securely in position for about 30 seconds. If hot water will be flowing through the pipe, don’t use it for 24 hours to give time for the joint to set completely.

Joining ring-seal types

Preparation for ring-seal or push-fit jointing is similar to that for solvent welding. The pipe end must be cut absolutely squarely and all the burr removed. You should draw a line round the cut end ot the pipe 10mm from its end and chamfer back to this line with a rasp or shaping tool, then clean the recess within the push-fit connector’s socket and check that the sealing ring is evenly seated. One manufacturer supplies sealing rings separately, and they should be inserted at this point. The pipe end should now be lubricated with a small amount of petroleum jelly and pushed firmly into the socket past the joint ring. Push it fully home and mark the insertion depth on the pipe with a pencil. Then withdraw it by 10mm (which is the allowance made for expansion). The expansion joint that is inserted into long straight lengths of solvent-welded waste pipe consists of a coupling with a solvent-weld joint at one end and a push-fit joint at the other.

As with solvent-weld jointing, individual manufacturers may give varying instructions. Some, for instance, advise the use of their own silicone lubricating jelly. Where the manufacturer supplies instructions it is best to follow these exactly.

Fittings

PVC pipe can be bent by the application of gentle heat from a blow-torch, but this technique needs practice and it is best to rely on purpose-made fittings. Sockets are used for joining straight lengths of pipe, tees for right-angled branches, and both 90° and 45° elbows are usually available. If you need to reduce the diameters from one pipe to another you can use reducing sockets. These are really sockets w.ithin sockets which can be welded together, one taking the smaller diameter pipe and the other the larger. Soil outlet pipes from Wcs are joined in the same way; they are merely bigger -usually 100mm (4in) – in diameter. Sockets work in the same way, but the branch-junction with the main soil stack must be of a specially ‘swept’ design.

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