Condensation or leak?

[thewickedpickett]

I have an external double skinned garage. I have recently turned it into a weightlifting area. I notice an area of the plaster is damp in rain and anything touching the wall is wet. I got a cheap damp monitor device and it is showing 16% in the areas that look damp. I should add the ‘normal’ picture of the plaster always looks ‘wet’ but it gets worse after rain. It is a pitched roof with tiles and felt stuff underneath. I have had gutters cleared in case it was that.

Can anyone advise what they think it is? The pic is from today when the damp looking areas are bigger and it’s been raining etc.

 

[23vc]

Penetrating damp looks like. What’s the outside, render?

Any dodgy gutter/downpipe on the outside?

 

[thewickedpickett]

That wall is cinder block then there’s a cavity and outside wall is red brick. I just had the gutters down pipes cleared so presumably not that. The down pipe is the other end of the garage too. I’ve had a look in the cavity with my phone camera and can’t see anything obvious.

 

[23vc]

Looks like the whole wall never dried out, given the visible blockwork