Do’s and Don’t’s for cementing plastic pipe systems

Do’s and Don’t’s for cementing plastic pipe systems 

·         Do chamfer the edges of a cut pipe. Chamfering is not, as many incorrectly believe, a process that enables the pipe and fitting to glide together more easily, although this can be an added benefit. The main purpose of chamfering the outside edge of a pipe before the application of cement is to allow as much of the cement as possible to enter the joint. A straight cut pipe without any chamfering will act as a blade, scraping off the solvent cement inside the socket.

·         Do use additional unions to make the process pipework easy to disassemble in the future. Although it is often difficult to imagine why a system might need to be taken apart, unions should still be added for good practice. A pipeline may require to be inspected, cleaned or modified, and if unions are installed then these processes become easier, reducing downtime in the future.

·         Although not always possible, do try to leave a short section of pipe between each fitting rather than butting them up right next to each other. A section of plastic pipe between the fittings should be a little longer then a socket depth for that size of pipe. Following this rule allows far easier adaptation of the pipework in the future, as a fitting can be cut out, leaving a spigot long enough to cement another one on.

·         Do work out where your last join will be about five or six joins before you get to it, and ensure there will be enough movement available to make the joint. It is often the case that inexperienced fitters get to the last join and realise it is to a wall connection or other immovable object, and there is not sufficient space to allow for the socket to be pushed on to the pipe. In such situations a remedy is to fit a short section of plastic pipe, with a union at either end, so that it can be removed to give movement to the plastic pipe system.

·         Don’t add cleaner to your cement to try to thin it down after leaving the led off for an extended period. This will result in a poorly performing and potentially leaking, joint. Whenever possible rest the lid of the cement tin back on top to prevent evaporation of the solvent. If the solvent cement becomes too thick to apply or lumpy, it should be discarded and a new tin opened.

Finally, remember that shortcuts taken when assembling plastic pipe system always bite back in the end!

Common errors made when cementing plastic pipe systems

Common errors made when cementing plastic pipe systems

ABS, CPVC and PVC pipes and fittings are generally connected to each other using a solvent weld process. After cleaning the pipe and fitting of any grease or dirt, a thin film of solvent cement is painted onto both surfaces and they are pushed together in one swift movement. The solvent cement melts a thin layer of plastic on the pipe and fitting and as the solvent evaporates, these layers fuse together to form a strong seal. This would appear to be a straight forward process. Like many such processes however, there are a few do’s and don’ts that need to be followed;

·         Don’t paint the solvent cement on to the pipe first. The socket should be coated first and then the pipe. This is because the socket can be put down on a surface whilst the pipe is painted. If the pipe were painted first, it is difficult to put it down anywhere without getting grit and dirt on the cement.

·         Don’t let solvent cement or cleaner run into a valve. If at all possible unscrew the unions, or remove the flanges from the valve, glue into position and then, once the cement has dried,, reassemble the valve. Care must be taken to ensure the union nuts or flange rings are on the pipe before cementing the fitting. If the valve must remain assembled, apply the cleaner / cement to one side of the valve and sit it vertically with the cemented socket facing downward whilst you apply cement to the pipe. Push the valve downwards onto the pipe and leave to set in this position. If it is suspected that cement may have entered the valve body, turn the handle a few times to ensure the mechanism remains free. In the case of an abs valve, this must be done very quickly as the setting rate for abs is very much faster than pvc pipe.

·         Don’t twist or turn the PlasticPipe Fittings  together as they are assembled. The error is often made by inexperienced workers, who believe that it will ensure the cement is spread throughout and give a better join. What in fact happens, especially with ABS pipe and fittings (as the y set much quicker) is that the moment the two surfaces come in to contact with each other, the solvents begin to melt the plastic surfaces and they begin to fuse together. Twisting the pipe / fitting tears the newly formed, fused layer and prevents it from forming correctly. This will result in a leaking joint.

Part two of this document includes additional do / don’t tips for pvc,abs and cpvc pipe and fittings.