Damp Patches on Entire Wall

Phil4432

Doesn't look like rising damp, but have you ruled that out?  Your house may not have a damp proof course, as is common with houses of that age.

Is there a driveway on the other side of that wall?  What's the surface drainage like?

Don't think this is the likely cause, but good to rule out.

Ben1989

Yeah there’s a drive but these stuff is all up the gable wall and we don’t see it on other walls. Driveway drainage is fine it’s just loose slabs. 

A new patch has appeared today. See picture below. It’s the one on the far right. I was starting to think it was condensation but why would a random patch appear especially when it’s getting warmer?

Ben1989

You can also see what seems to be a pattern of bricks 

Ben1989

I have a meter now. What’s the best way to use it?

markin

What kind of meter?

Ben1989

Moisture meter 

danrv

Sounds like you’ve done a lot of work on the outside of the wall and inside. I wouldn’t be in any hurry to rerender the outside if it’s not a common problem with the other properties. Is the damp present all year round or only after heavy rain? Maybe it’s not a problem in the summer months.
Has to be something to do with the wall type/construction. I have an exposed gable wall.
1970’s cavity insulated and no damp problem. 
Similar topic here:
https://www.mybuilder.com/questions/v/16184/penetrating-damp-on-rendered-gable-end-wall-in-victorian-end-of-terrace

markin

With 2 probes you pess on the wall or into wood?

Not sure why you need one, you can see where the damp is?

Ben1989

Yes that's the one

markin

I guess you can just go over the wall in a 1ft grid patern, useing even gentle pressure.