This winter I have noticed efflorescence on the top portion of my chimney. The top six rows were rebuilt two years ago. I didn't notice it last year, but perhaps I just didn't see it.
Oddly, it seems to be confined to the portion that was rebuilt, as you can see from the photos. ( The two bricks in the lower left were individually replaced ). Also there seems to be a little more towards the back.
Small grey spots in the mortar are places where I did some touch up on the mortar.
My first thought was that warm moist air is moving up from inside the house and coming through the brick at the top. I had a wood stove insert installed. In order to make it fit, they had to open up a row of fire brick. The hole was filled with Roxul insulation.
As you can see, there is a metal flashing that should be keeping everything dry.
Should there be weep holes this high up on the chimney ?
Is the efflorescence the result of new brick and mortar ? Thus why it is not appearing on the old brick.