Lead pipe

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Lead is a soft malleable metal often used in building since it produces an attractive and durable waterproof covering and finishing material. Ideal for roof and flashing work. Historically it was also commonly used for water and gas pipes. Although much of this has been replaced with more modern materials, there are still significant quantities in use in older properties. This article discusses some of the issues that come up with lead pipe, and provides some useful data on pipe sizing.

Lead pipe sizes

Lead pipe sizes are specified by both size and weight. The size is a measure of the internal pipe diameter in inches. The weight is specified pounds / yard. So heavier pipes of a given internal diameter achieve the same flow rates as lighter ones, but have thicker pipe walls, are physically more robust, and can operate at higher pressures.

Data collected from various sources and BS 602-1970
Pipe weight (lbs) External diameter (inches) External diameter (mm) Max working pressure (Bar) Comments
1/2" Pipe
5 54/64" 21.43 4.5 Some references show the nominal outside diameter for 1/2" 5lb pipe as 53/64" (21.03mm)
6 7/8" 22.23 4.5 Note that working pressures are approximate, and are specified when carrying cold water. For use with hot water the pressures are typically reduced to approx 45% of the cold pressure.
7 59/64" 23.42 7.5
9 1-1/64" 25.80 10.5
3/4" Pipe
6 1-3/64" 26.59
8 1-1/8" 28.58
9 1-5/32" 29.37 4.5
11 1-15/64" 31.35 7.5
12 1-17/64" 32.15
15 1-23/64" 34.53 9.0


Careful measuring is required since the difference in external diameters is quite small. Find a clean non distorted section of pipe away from and tight bends and use a calliper gauge to read the diameter directly, or wind a thin slip of paper or length of cotton round the pipe and draw a line across it where it overlaps. Now measure the distance between the lines and divide by π (3.14159) to get the diameter.

Working with lead pipe

Lead pipes have been in use for plumbing since Roman times, since it is a durable material that was relatively easy to work by hand. However the skills required to do new plumbing installation using lead pipework have dwindled since it is very unlikely to be used for new work.Modern plumbers are not usually trained in lead use for plumbing (although lead work for flashing and roofing is still included in many plumbing courses).

This has tended to render most plumbing on lead pipe to either complete replacement, or to transition from lead to copper at the earliest opportunity, and then complete all subsequent work in copper or plastic.

Fixing leaks in lead pipes


Sometimes pin hole leaks can open up in lead pipes - especially when they are bent, or moved, or hit by something. Small leaks can sometimes be fixed by tapping with a small hammer close to the leak. This allows some metal to be "moved" over / into the crack / hole, and close the gap.


Patches can be applied using a sealing material like some thin rubber sheet, that is held in place with a clip of some kind. Stainless steel jubilee clips can work well. Mild steel ones are less favoured since they will tend to rust and fail with time.

Small leaks can also be taped up using multiple turns of putty impregnate cloth tape like Denso or Sygalss tape. This is wound around the pipe (using disposable gloves - it is very messy to work with), and then smoothed / rubbed into place.


Metal or wood plugs can be driven into holes to plug them. Again these may require retaining with a clip of some kind. Hardwood plugs were traditionally used since they teed to expand slightly when wet, keeping them tightly held in the hole.

Connecting modern pipes to lead pipes

Using a transition fitting

There are a variety of transition fittings available on the market, that are designed to fix onto the end of a lead pipe, and allow connection to a modern pipe style. These allow connection to copper, plastic, and steel pipes.

Most are types of compression fitting. There are brass bodied ones which look quite similar to a traditional compression fitting. Often you need to select the right sized fitting for the lead pipe in question.

There are also plastic bodied transition fittings that use larger rubber O rings, that can usually accommodate a range of lead pipe sizes.

Lead to copper transition - soldered

This is an intermediate skill level job - not as difficult as a full on "wiped joint", but it takes a bit more preparation and care than soldering joints on copper pipes. The main issue with soldered joints on lead pipes is that there are no lead "fittings" (at least for common small pipe sizes), and the pipe itself is essentially made from the same stuff as solder - so the melting point of the pipe will be fairly close to that of plumbing solder.

To do this you will need a blowtorch with a controllable flame, plenty of flux, and a traditional 60/40 lead/tin plumbers solder.

Note for soldering to lead pipes you must use a traditional lead/tin plumbing solder. "Lead free" solder is not suitable (and kind of pointless when you think about it!)

  • You start by swaging / flaring / reaming / drilling the end of the lead pipe to make it wide enough to allow a stub of copper pipe to be inserted into the end of the lead pipe.
  • Clean up the end / interior of the lead pipe so that it is bright and clean
  • Cut your stub of copper to be four to five inches in length (100 - 125mm).
  • Debur and clean the end of the copper so it is bright and shiny
  • Insert the copper in the end of the lead with plenty of flux. Ideally you need the copper pipe to insert about an inch / 25mm deep.
  • Then *gently* start heating the copper pipe with a soft flame - not letting the flame play on the lead directly - allow the copper pipe to transfer heat to the lead. The idea being to get the copper up to soldering temp, and just on the verge of melting the inner surface of lead it is touching. You can test progress by touching the copper with your solder - it will start to "wet" the pipe as the temperature reaches the right level
  • Then start "touching in" the solder all around the joint - you will see it be drawn into the joint. Slowly add more, allowing a little time between each addition. You should be able to get a decent fillet of solder into and around the joint, which is properly bonded to the end of the lead.

It will take a number of minutes to complete the joint.

Lead to copper transition - wiped joint

This is the traditional jointing process - usually used for lead to lead joints in plumbing. It uses a separate crucible to heat a quantity of solder. The then molten solder is then splashed onto the well fluxed joint using a splash stick, and the solder then wiped with a flux impregnated "moleskin" (a dense cotton cloth with a soft pile on one side). The final joint results in substantial mass of new metal that surrounds and encloses the joint, making it water tight and also mechanically very strong.

Note the Society for the Protection of Ancient Buildings (SPAB) have a document on lead working available here.

Lead toxicity

The toxicity of lead is one of the many reasons why it use is not favoured for transport of potable or wholesome drinking water today, since in soft water areas the lead can leach into the drinking water, which is a health hazard.

Note that in areas with hard water, a yellow / orange scale tends to form inside old lead pipes, and this provides a barrier that separates the water from the lead. So left undisturbed, little or no lead should continue to leach into the water.