What is this staining on my wall joints?

[PaulUszak]

I've taken the following two pictures of the brickwork by my patio:-

Untitled

• PaulUszak
• 8 Jun 2015
• 1

Untitled

• PaulUszak
• 8 Jun 2015
• 1

The brickwork is between the patio flags (the beige area at the bottom of the image) and the patio door cill (the black bit at the top). The white staining only occurs under the length of the cill, between two weep holes either side of it. There is no staining anywhere else on the entire wall. The pointing seems to be cracking, and the dark areas (such as in the lower photo) seem damp, or at least cold to the touch. The DPC runs just below the underside of the door cill.

The white marks have only been noticed this year. Three years or so ago we had cavity wall insulation blown in. The house is 20 years old and in good condition otherwise.

What is the white stuff please..?

 

[PaulUszak]

Any ideas anyone? Do I need to worry?

 

[^woody^]

Efflorescence. Not harmful.

 

[PaulUszak]

Efflorescence

Are you sure?

There is water actually oozing out of the cracks. Not quickly, but enough to not be evaporated during this summers hot days. Also you can see that the mortar is disintegrating. as mentioned, this only happens between two adjacent weep grills.

Seems harmful to me ...

 

[tony1851]

Just a guess here but split mortar joints sometimes suggest sulphate attack due to excessive dampness?

 

[^woody^]

Are you sure

Yes I'm sure that the staining is effloresence.

If your question should have been "What's all this water coming out of this crack" Then that will be a different answer.

That looks like it's got a DPC or cavity tray in that joint, which has caused the crack and the concentration of water.