How to apply PTFE tape

When it comes to plumbing jobs, you will inevitably have to make a seal at some point. PTFE tape is a popular choice as it is generally thought to be the easiest solution. However, not everyone knows how to apply it correctly!

In fact, PTFE tape isn't all that easy to use. What's more, if it's not applied correctly, the chances of your seal leaking or dripping are much higher compared to other techniques.

PTFE tape features

PTFE tape can be called a few different things (including plumber's tape or thread seal tape), but you'll usually find the abbreviation PTFE on the packaging which stands for 'polytetrafluoroethylene'. PTFE tape is usually white but can come in different colours; yellow tape, for example, is used for gas lines. The tape is not sticky but rather stretches around threads to create a watertight seal.

It varies in thickness but is commonly 0.076 mm, 0.08 mm or 0.2 mm thick. The thickest tape can be used for large connections as it is so thick you won't have to use as much (9 or 10 turns in general).

PTFE tape can be used on any fixed threaded connection and is often the best solution in these cases.

It is, however, not suitable for use on compression fittings; the components of these fittings are made watertight through the use of a compression nut and do not have to be sealed. In fact, it is even counter-productive to apply PTFE tape over these threads.

PTFE works best on soft mating surfaces as hard surfaces can cut the tape which will lead to leaks. 

PTFE tape applications

Firstly, PTFE tape can be used on any plastic threaded connections and works particularly well for this type of application. These days, plastic is used for more and more plumbing components, including:

• toilet fill valves;
• cartridge filter kits for water filters;
• hose connections;
• HDPE (high-density polyethylene) plastic fittings.

PTFE tape can work very well for these components whether you are connecting two plastic parts or connecting a plastic fitting to a metal fitting. This is because a PTFE seal works best when it's not overtightened, just like plastic fittings. 

PTFE tape is also great for delicate components such as pressure gauges. Finally, PTFE can be used to assemble components that are likely to be disassembled, such as: 

• water pump pressure switches;
• pressure sensors;
• any other type of sensor.

If any of these devices break down, a PTFE seal will be much easier to remove than other types of seal, which means you won't have to apply force and risk damaging your pipework. 

1. Applying PTFE tape to the joint
2. Tightening the joint with the PTFE in place

PTFE tape should be applied to the male thread that enters into the female thread.

Start by identifying this part of the fitting.

Check the direction in which the fitting is tightened. It is important that the PTFE tape is applied in the direction of tightening (usually clockwise).

This way, when you tighten the joint, the PTFE will compress. If you apply it in the opposite direction, the PTFE tape will loosen as you tighten the joint. Next, roll the tape around the connection. When doing so, the tape must be held taut so that each layer overlaps with the previous layer. 

Now you can determine how many turns you need to make; this can be the trickiest part of using PTFE tape. The number of turns will depend on the diameter of your fitting and the type of connection. The space between threads varies slightly between different manufacturers and you'll need to adjust the number of turns accordingly. For 0.2mm PTFE tape, around 9 to 10 turns should suffice. 

PTFE tape should never be tightened too much in order to prevent the threads from cutting into the tape. In some cases, tightening can be done by hand (for example, installing a valve). Otherwise, use the appropriate tool for your task such as an adjustable spanner or pliers, an open ended spanner and so on.

Thread sealing cord: an alternative to PTFE tape 

PTFE tape does still present a risk of leaks or dripping. If you find that this is the case, it is possible to use a slightly different PTFE product; PTFE or thread sealing cord, for example, can create a more effective seal. This cord is white and slightly waxed. It is designed to be wound around the threads of the fitting in the same way as PTFE tape. The packaging should indicate how many turns you'll need to make according to the diameter of your fitting. This cord is very resistant – contrary to PTFE tape which can be torn by hand. Once you've rolled the cord around and tightened the fitting, the risk of leaks is minimal. Thread sealing cord is therefore recommended for general use while PTFE tape is best reserved for the applications described above. 

PTFE tape FAQs

Can I loosen my connection if I've overtightened? No, PTFE cannot be moved around in the same way as an old-fashioned oakum seal. It is not advisable to touch any PTFE seal once it is in place (unless you have a leak). 

Can I use PTFE on a compression fitting? No, this is counter-productive. The compression nut is designed to hold the joint together. Applying PTFE tape around the thread will prevent the nut from tightening correctly. 

Can I put PTFE tape around my waste trap? Waste traps come with their own seals. It is not necessary to put anything on top of these seals. However, if you have an old joint that is leaking, you can try to use some PTFE for a temporary fix. 

So, there you have it: you are armed with everything you need to know about PTFE tape. Now all that's left to do is to tape up your connections and get the taps running!

Time required

5 minutes

Number of people required

1

Tools and equipment

• Open ended spanner
• Adjustable pliers or spanner (depending on situation)
• PTFE tape