Quite unconnected with my big leak, I have a smaller leak I need help with

[KatyMac]

My big leak happened last Wednesday & is unconnected with my smaller leak which appeared as a damp patch about 3 weeks ago

It is close to where a pipe goes through the wall, but both sides of the pipe is dry.

Is it likely that the pipe has split within the wall?

[PigletJohn]

not very likely.

is it a cold pipe in a warm room?

condensation.

is it a pipe passing into a rainy area?

rain.

[KatyMac]

It used to be an external wall - now it's inside the conservatory

The conservatory floor has underfloor heating

The pipe is the utility sink drain which comes through the wall & joins the main water out of the house pipe about 2m further on

Thanks for answering PigletJohn; you have given me such good advise (esp last week)

[PigletJohn]

it's a plastic pipe?

does it seem to be under any bending force, or will it wiggle freely?

[KatyMac]

It's rigid plastic - there is a joint either side

My dad is flumoxed - he spent years as a building contractor but has been management for decades

I wonder if the cladding/outside finish has come away from the wall & water is getting in. It was one of those only halfway up the wall thick coating painted cream, then plastered over once it was inside

[KatyMac]

It is cemented/mortored in

[PigletJohn]

it is possible, but quite difficult, to crack a uPVC pipe, mostly by a heavy object falling on and stressing it. The crack is more likely to be at the edge of the wall than inside it. It would be abnormal to have a joint in a pipe inside the wall.

If it is a cavity wall, it might be that water is entering the cavity from above, perhaps from a defective roof or gutter, very rarely from a plumbing leak, and dripping onto the pipe, or filling up the cavity and leaking out of the hole round the pipe.

[KatyMac]

Could it be either cold bridge condensation

or that the pipe gets condensation round it with in the wall

& then we put the heating on?

[PigletJohn]

Metal pipes often get condensation, plastic pipes don't.

What runs through it?

Is the wall damp?

[KatyMac]

The plastic one has waste from a utility sink - so washing craft stuff, hands, cleaning etc

The metal one about 10 inches to the left has premixed warm water for the children's sink

[PigletJohn]

Might the metal pipe be leaking or getting condensation when cold?

Leaks are more common at joints but water may run down or along the pipe

Is there a wet window above?

[KatyMac]

No window above

The damp patch is about 2 foot from the metal pipe & above it

[PigletJohn]

Tie kitchen roll tightly round all pipes on both sides of the wall.

[KatyMac]

Sorry that isn't true there is a window above the metal pipe but it's an internal window between the utility & the children's toilet

[KatyMac]

I'll try that tomorrow - good idea

[PigletJohn]

Is condensation or rain coming from the window? Is it a cavity wall (13 inches thick) or a solid wall (9 inches)?

[KatyMac]

13 I think; it's a 1950s ex council house - so I expect so

The window is between 2 rooms so it sees no rain and no condensation

[PigletJohn]

Is there a flat roof above this wall? Might. there be an old water pipe chased into it and plastered over?

[KatyMac]

Nope - it's the rear elevation of the house - normal roof

My dad is tearing his hair out tbh he cannot 'find' a reason

[KatyMac]

There is obviously a conservatory roof over it but I'm kinda hoping that's OK as there is no visible water

[PigletJohn]

Is it worse in rainy weather, or better after a day when the sink has not been used?

When did it start happening? I would be thinking of chipping some plaster off to look at the bricks. It might be hydroscopic salts from old damp.

[KatyMac]

I'll track it over the next few days

It started about when the temp dropped & I put the heating on (I think)

Chipping off is all we can think of to do - thanks