Damp on internal wall?

[Mike13]

So then there is either hygroscopic salts in the wall OR a bridge across the damp proof course.

 

[Tentontousand]

You mean from a watermain in an alley behind the houses, rather than from a main under in the road to the front, with a communication pipe passing under the house floor?

Mains pipe is supplied from our back into our kitchen which supplies the rest of the house. No water supply from front.

 

[Mike13]

The mains supply normally passes as a bigger pipe in the road with a tap and smaller pipe for each property, from the road it goes through your garden and into the house somewhere, that is the pipe referred to above.

 

[Tentontousand]

The mains supply normally passes as a bigger pipe in the road with a tap and smaller pipe for each property, from the road it goes through your garden and into the house somewhere, that is the pipe referred to above.

Yeah it's supplied from the pipes behind. We have a road behind our house (very small courtyard size garden) so mains comes from there.

 

[Mike13]

ok, so either the damp proof course has a localised failure or it is bridged or there are hygroscopic salts in a few bricks on that bit of the wall.
First step, clear all the plaster from around the ground level so that you can clearly see clean bricks at the level of the damp proof course, dont need to go high, just up to about top of skirting board should be enough. then wait a week or two to see if it starts drying