Last edited 12 Oct 2018

Which way up should you lay a brick?

Bricks are small rectangular blocks that can be used to form parts of buildings, typically walls. Bricks are often completely solid, but they can also have holes perforated through them to reduce the amount of material used.

If bricks are perforated, or completely solid, it generally does not matter which way up they are laid.

However, some bricks have an indentation on one surface (or on two opposing surfaces). This is commonly called a ‘frog’.

London brick with frog.jpg
By Nottsexminer - London Brick Company #3, CC BY-SA 2.0,

The frog reduces the amount of material used to form the brick, makes it easier to remove from the form, and gives the completed wall better shear resistance. It may also help heat reach the centre of clay bricks in the kiln.

It is thought that the word frog is a translation of the Dutch word 'kikker' and refers to a kicker placed in the bottom of the wooden boxes traditionally used to make clay bricks, which forced the clay material outwards when the brick was being formed.

The frog must be filled with mortar when bricks are laid otherwise the structural, thermal and acoustic performance of the wall can be affected. For this reason it is best practice to lay bricks with the frog facing upwards so that it is easy to fill completely and so that the mortar does not fall out when it is being laid.

Where there are two frogs, the larger frog should face upwards.

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