Strange crumbling mortar

[ljstrawson]

I have a wall in my sunroom that has crumbling mortar it's only one part of the wall which has patio doors in, its only the left side above and to the right of the door is fine. The wall the other side of the window is fine it's literally only the inside of the sunroom.

Any ideas what could be the reason?

Please see pictures below
https://www.dropbox.com/s/sebmmrgeenonzxm/2013-05-02 18.53.34.jpg
https://www.dropbox.com/s/npe75p8cs0wyd6m/2013-05-02 18.53.29.jpg

 

[pinenot]

Interior or exterior hard to tell from your picks!

 

[ljstrawson]

It's an exterior wall but its in the sunroom.

Right of the glass (problem area) in the sunroom, left of glass is outside

 

[tony1851]

Probably just mortar that's too soft (ie not enough cement in the mix).

 

[pinenot]

First thought is direct sunlight, would that fit the bill?

 

[tony1851]

First thought is direct sunlight, would that fit the bill?

Never heard of that one.

Maybe pinenot will be along shortly to give us all the benefit of his inexhaustible mine of knowledge of building construction, and life.

 

[^woody^]

First thought is direct sunlight

Seriously?

 

[ljstrawson]

It is in the sun most of the day. But also happens in the winter didn't think it would be hot enough? We've only lived here 6 months so not what it was like before.

 

[stuart45]

First thought is direct sunlight

Seriously?

pinenot is spot on woody. In California Factor 80 is always applied to the joints because of this problem.
The mortar does like a really sandy mix, about 15/1.