Newly found damp - not sure what it is?

hbadami

Hi

We have a semi detached house and recently we are trying to convert the area under the stair case (which was earlier inaccessible) to a small store room. When the builder opened up the space and put in the wooden flooring, we saw a damp mark, which I am not sure if its due to condensation or is rising/penetrating damp. Please help me identify what kind it is and any recommendations on what should be the way forward. I have attached the inside and outside pictures.
Thanks in advance.
Hass.
External wall 





Internal Wall

grumbler

Doesn't look like condensation to me.

And is is an extension? What do you know about it?

Doozergirl

Is the render plinth on the other side of it?  Remove the plinth.  People put them in thinking they prevent damp for some reason, but they cause it! 

Where is the internal floor level compared to outside? 

hbadami

@grumbler No its not an extension, its underneath the main house building stairs.
@Doozergirl Yes its the render plinth. I was thinking of getting it removed and plaster 1 foot or so up from the floor. The internal floor level is where you see the plinth ending (height wise).

Doozergirl

hbadami said:

@grumbler No its not an extension, its underneath the main house building stairs.
@Doozergirl Yes its the render plinth. I was thinking of getting it removed and plaster 1 foot or so up from the floor. The internal floor level is where you see the plinth ending (height wise).

It looks like it needs plastering inside anyway as that looks a bit like render.  I'd take that off the wall as well.  

Is the walkway outside?  Ideally you should cut back that concrete running up to the wall and put in a french drain with gravel.  At the monent all the run off is probably trying to escape to the ground in any cracks directly against the house.   You want to give it some ground to drain to instead. 

hbadami

@Doozergirl Do you mean it needs plastering inside or outside? I am guessing you mean the plinth outside, which I plan to remove and plaster. Yes its a walkway outside. I will see what can be done to put a french drain there.

FreeBear

Doozergirl said: It looks like it needs plastering inside anyway as that looks a bit like render.  I'd take that off the wall as well. 

I'm wondering how far down that internal render goes - If it is bridging the DPC below the floorboards, it will suck up moisture from below. Lift the boards, remove as much of the render as possible. Reinstate the floorboards, and plaster down to them. Preferably use a pure lime plaster as it will tolerate the occasional period of dampness much better than gypsum.

princeofpounds

Is there a DPC in your brickwork? 

stuart45

What's the newer brickwork next to it? Is that an extension?

Doozergirl

hbadami said:

@Doozergirl Do you mean it needs plastering inside or outside? I am guessing you mean the plinth outside, which I plan to remove and plaster. Yes its a walkway outside. I will see what can be done to put a french drain there.

I'm talking about inside, which freebear adds to, making a very good point. 

You don't plaster the outside.  You take off the plinth and leave well alone.  

hbadami

Thanks guys for your response. Very helpful. Reading the comments generally it seems friends here think its rising from the ground up and does not seem to be condensation. Agree? 
When we bought the house it had damp issues and I had to get the DPC injections in all the external walls (from inside) since this space wasnt opened up we didnt get this done. But this is a very small space, hardly 6ft and injections have been put in on either side of this space.  This is a 1930s house, the newer bricks you see, used to be an external door which was shut by the previous owners (dont know when). Nothing external seems to be the issue here, I see no external pipes/drain nothing around that area. I even touched the plinth and the surrounding bricks, they dont seem to be wet.