Brickwork effervescence problem

[michael]

During the summer of 2011, I had to dismantle and rebuild the top 12 courses of a 130 year old wall that had become unstable. The wall in question supports a lean-to roof however everything from the lean-to roof rafters downwards was sound and stable but everything above i.e. the top 12 courses of the wall, including the brickwork capping and dogtooth detailing at the top of the wall was at a point close to collapse.

I discovered on dismantling these 12 brickwork courses that a timber wall plate, designed to support the lean-to rafters and installed when the structure was originally built, had rotted in the wall making the brickwork above it unstable. It would seem that the previous owners had installed a new timber support system for the rafters within the loft of the lean-to, which seems quite satisfactory but they had failed to remove the old timber wall plate in the wall. Anyway, all has been rectified, the rotten wood was removed and the wall was rebuilt, salvaging most of the original bricks.

Almost two years on, and I have discovered in the last week or so that a white salt effervescence is forming on the 13th brickwork course down from the top of the wall i.e. the undisturbed course upon which the rebuild was laid. This course is a good seven feet above ground level. The 12 courses above this i.e. the rebuilt part of the wall has no effervescence.

Any ideas as to what might be causing this?

 

[michael]

P.S. Mortar mix for rebuild was 3x sharp sand to 1x NHL 3.5 with a small scoop of lime putty thrown into the mix.

 

[middi]

What you are describing ( effeverscence) is usually attributed to mineral salt deposits that leach out from newly costructed walls and can be apparent for a few years untill all the minerals have been leached out of the wall.
In your case, and especially if some new bricks have been used, these mineral have been washed out and leached onto the undisturbed and existing bricks creating the "illusion" of foamy and salty deposit at this level.
The intensity of these deposits vary according to masonary constitution and mortar. One thing is certain, there should be no need to concern yourself with this phenomenen, eventually the masonary minerals will be slowly washed out and everything will look normal.

Middi

 

[stuart45]

Although efflorescence is normally caused by salts in new brickwork there can also be some in the sand. Calcium oxide can also be washed out to the surface and form calcium carbonate on the surface of the facework.