Frog up or Frog down when laying bricks

A frog can make all the difference when it comes to your bricklaying. Learn whether you should use frog up or frog down to lay your bricks perfectly every time.

Why is it Called a Frog?

Frogging – creating a frog in the brick – is believed to originate from Ancient Egypt. It was custom to create hollows in the bricks, made from Nile clay, and inter live animals. Ancient Egyptians saw the frog as a symbol of fertility and life-giving. Some Egyptologists believe the animals were interred to assist the pharaoh in their afterlife.

The term frog has many meaning, aside from the amphibian reference. It is the term for a loop for holding a weapon, such as a sword, or a tool, such as in scaffolding. It also a term for the ornamental braiding that fastens the front of a garment. It is therefore entirely possible that the frog recess was named for its ability to provide superior bond between bricks.

Another possible origination of the name is associated with the bumps in the bottom of the brick mould, that form the frog indentation. Early brickmakers had to ensure that green clay filled all the corners of the brick mould. The wooden bumps in old brick moulds were called “kickers” because they “kicked” out the clay into the corners. At some point in history, the English word “kicker” became confused with the Dutch word “kikker”, which translates as “frog”. Other people believe the bumps themselves resembled crouching frogs.

Up or Down?

Some experts say that bricks containing frogs should be laid frog up so that the frog is completely filled with mortar. If the brick is laid frog down, the frog may not be completely filled with mortar. This would render the brick wall face-shell bedded, which gives less wall strength than full mortar bedding. 

Other experts say brick should be laid with frog down, for two reasons. First, a uniform bed of mortar can be laid more easily on the face that doesn’t contain the frog. Second, if the frog is laid up, any cavities left can hold water, which may cause frost damage and contribute to early brick deterioration. 

Some believe frog down is stronger, resulting in better cement adhesion and a stronger bond between bricks. 

Others believe frog up has better strength properties. The load is evenly spread throughout the width of the brick, all the way to its foundations. The debate has raged for generations.

The British Standard

According to British Standard Code of Practice BS 5628-3, bricks should be laid frog upward and filled with mortar to maximise strength, stability and general performance of the brickwork.

“Unless otherwise advised, lay single frog bricks with frog uppermost and double frogged with deeper frog uppermost. Fill all frogs with mortar…” 

If a brick is laid this way, the crease turns up and looks happy. And we all want a happy brick.

So, now you know.