Wall crack

FreeBear

Solid brick wall, chipped off the top layer of pebble dash, and revealed this crack. The base coat of render appears to be a hard cement based coating, and has a number of fine cracks at random angles & places (due to shrinkage ?) - This all dates from around 1928/9.

Comments/thoughts ?

stuart45

The crack could be in the mortar joint as well. Probably nothing serious.
Horizontal cracks in render are sometimes a sulphate attack expanding the joint a bit. Could be a rusty frame cramp. 
Occasionally with a hip roof pressure on the corner moves the brickwork a bit, but it's usually the top course that goes.
Might be worth cutting out a bit of render to see the joint.

FreeBear

I'll be grinding out this, and other cracks, so will take a look. Doesn't appear to be any ironwork in the wall apart from a couple of cut clasp nails used to fix a downpipe clip. Sulphate attack would surely be random patches & cause blisters rather than straight cracks ?

Will post more pics once I've attacked it with the grinder

Rdwill

I'd say that is where the renderer stopped for a cup of tea.

stuart45

FreeBear said:

 Sulphate attack would surely be random patches & cause blisters rather than straight cracks

It can cause cracks like that in the render, as the bed joints in the brickwork expand. It's more likely when a wall is rendered, but can happen on face brickwork. 
Most common where the wall is exposed to driving rain. Causes chimney stacks to bend as one side of the stack gets bigger bed joints.

FreeBear

Lime mortar used between the bricks which I believe is immune to sulphate attack.

stuart45

Less likely, but not totally immune. The period of your build often used lime mortar with a small amount of OPC gauged into the mix.
It could be pure lime, or gauged mortar, the 2 are very similar in appearance.
When you open up the crack you will have a better idea. Sulphate attacked joints are usually crumbling, and often are white.

FreeBear

Opened up a small section of the crack. Right on top of a mortar joint.

The mortar between the bricks is a sandy colour and friable (like all the mortar in this building). Loading from the hip causing a slip in the mortar bed sounds like the most reasonable explanation.

stuart45

There is quite a load on the plate in the corner of a hip roof. A Dragon piece or tie was often put in to help with this issue.
It probably won't go any further.