Building foundations under Brick Walls

The Yellow Brick Wall

The illustration shows a very soft yellow brick, in a school built in 1996. This drawing was made about thirty years later. In that time the corner of the wall has been broken away (abraded) by people brushing past and barrows knocking pieces off it at the corners. It was certainly a very soft brick. In cold weather the water in the bricks froze, expanded, and broke the brick away. In the end the damage was so bad that the bottom of the wall had to he repaired with a skirting of sand and cement.

In this corner the foundations had sunk slightly, putting strain on the bricks. In some places the mortar has clung to one brick and broken away from the next so that two bricks, side by side, are no longer joined. In other places the mortar has held securely, but the bricks themselves have broken. This tells us a lot about the mortar: it was much too hard for the brick.


Cracked bricks and failed mortar lines in the yellow brick wall.

 

Hard and Soft Mortars

Mortars are usually made of sand, lime and Portland cement in different proportions. Other things have been used at other times and in different places. Rascally builders have saved money by using street sweepings, ashes and horse manure. Good mortars have included animal hair to hold the mortar together. For example, the famous bridge at Mostar, in Croatia, built by the Ottomans, had a mortar containing goat hair and white of egg. Different architects have had different preferences, but most mortars are of builders sand (soft sand, not sharp seaside sand) lime and Portland cement. The more cement, the harder the mortar: the more lime or sand, the weaker the mortar. The mortar in the yellow brick wall was strong, with plenty of cement. It was so strong that when the wall came under strain, it tore bricks apart while the mortar remained intact.

When the foundations are not secure they can sag under the weight of a wall. If the mortar is strong bricks can be torn apart. If the mortar is soft, the bricks can slide slightly, allowing the wall to sag to fit the ground. Many old houses can be seen to have sagged in this way. Walls are not quite straight. Window heads are at an angle, with the windows unable to close properly, yet the houses have not fallen down, or cracked. This is because the mortar was weak enough to allow the bricks in the structure to move slightly.


18th century crinkle crankle wall, at Henham, Suffolk.

 

Crinkle-crankle walls

This use of curved brick walls was developed for building estate walls in the eastern counties of England and later taken by John Adams to America. For a long time it was thought to be an American invention.

In the eastern counties of Essex, Suffolk and Norfolk the ground is soft, so that strong, stable foundations would have been difficult and expensive to build. Instead they invented 'crinkle-crankle' walls which twist and turn their way across the ground. If the foundations of any section sank, the soft mortar allowed the wall to slump. The wall stayed complete but the curve changed. Try this with a long strip of stiff paper, holding it in a crinkle-crinkle shape and allowing one curve to sink over the edge of the table. The curves will subtly alter, sinking and leaning.

The only crinkle-crankle walls I know of in Stoke Newington are garden walls at the top of Albion Road. The first block of houses which Cubitt built there, in the 1830s, have single thickness brick walls built in the crinkle-crankle shape. The ground here is gravel so the foundations would have been fairly secure, but by making the walls only one brick thick Cubitt save a lot of bricks. Who knows whether safety or economy was in his mind when he built in this way?

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