Condensation vs leak

[jgh]

Did a spring clean of the bathroom today, decanting all the movable furniture out and a hand-on-knees deep scrub of everything. I found a damp patch in the plaster behind a cold water pipe near to a T junction. This is right next to the shower, so could well be condensation rather than a leak. Is there any simple way of telling before I attempt resoldering/replacing the T junction?

I only discovered it because I haven't got around to boxing that pipework in yet, so I want to know I've fixed it before it gets hidden away and happily rots the wall unseen.

[Harry Bloomfield]

[e-mail] explained on 15/08/2017 :

Leave the pipe unused for several hours, so as to allow it to achieve the same temperature as it surroundings, maybe wipe away any moisture in the meantime. If after that there is still moisture on the pipe, it is due to a leak rather than condensation.

You can deter condensation to some extent, by insulating pipes.

[Thomas Prufer]

Tape clear plastic/plastic film to the wall. Leave for a while.

Moisture on it: condensation, under it: leak (or residual moisture in the wall from condensation).

Thomas Prufer

[Thomas Prufer]

eh, just re-read the post.

Adjust what I said for where the pipe is, and where the cold is coming from...

Thomas Prufer

[jgh]

I pulled all the insulation off, dried all the pipework, then tied lengths of tissue paper at strategic positions. By the position of the one soggy length of paper it's confirmed it's a teeny tiny leak from a capillary == join. Probably easiest to chop out a decent length of pipe to the next == join. Bugger that it's the rising main, it means shutting the whole house off.

[Michael Chare]

I would just remove the old joint, clean the pipe ends with emery cloth and maybe a maybe a file so that they are shining put flux on the pipe and resolder using a new joint.

The pipes must be clear of water to unsolder and then resolder.