A Quick Guide to Brick Frogs and Their Origins
Facing bricks are some of the most frequently used, reliable and versatile building materials. Architects worldwide rely on expert brick suppliers like Modular Clay Products to provide high-quality bricks, ranging from glazed bricks to long format bricks, to bring their architectural visions to life.
For the most part, bricks are completely solid and uniform, but they can have holes perforated through them, which would be the case if brick manufacturers and factories were trying to conserve materials. Generally speaking, this does not affect the brick’s structural integrity. However, some clay bricks have indentations on one surface (or on two opposing surfaces), commonly known as a brick ‘frog’.
What is a Brick Frog?
Brick frogs are indentations, which usually contain a brick manufacturer’s stamp.
The majority of UK bricks made with frogs are used for construction purposes. Refractory bricks were not made with frogs as builders required a tighter fit to minimise the cement used. In addition, cement was more susceptible to thermal damage, and as such, clay pavers did not contain frogs, as this would have meant they would accumulate water, which would spill onto the surface
Brick frogs reduce the brick weight slightly and make them easier to handle.
Origins of the Term ‘Brick Frog’
Several theories have made the rounds concerning brick frog origins, in terms of its terminology anyway.
Some suggest that the term ‘frog’ refers to the shape of indentations put in horses’ hooves, which extended to bricks down the line.
Historically, the bumps in the bottom of brick moulds – which are designed to force clay to corners – looked like crouching frogs. So naturally, brickmakers back in the day had to ensure clay filled all of the moulds, and this led to an introduction of raised blocks or kicks being fixed to stock boards to form the brick frog.
The theory with the most traction is that wooden bumps in old brick moulds were called ‘kickers’ due to them kicking out the excess clay towards the edges. It’s not exactly clear as to how, but somewhere the English work ‘kicker’ became repeatedly interchanged with the Dutch word ‘kikker’, which translates to ‘frog’.
Other theories exist which state that the indentations – which exist to reduce the amount of clay used – are in place to encourage frugality with clay, from a bricklayer’s perspective, at least. ‘Frog’ could be a play on the word ‘frugal’.
While it’s likely that brick frog origins will remain a mystery, their practicality and purpose can’t be underestimated.
What is the Size of a Frog in a UK Brick?
There is no universally accepted brick frog size, as it depends on the brick size for a start. There also is no general consensus that bricks with frogs should be laid in a certain way, as the indentation doesn’t affect its structural performance.
Frogs can’t be closer than ¾ of an inch to any brick edge. In terms of their depth, any frog that exceeds ⅜ of an inch deep is treated the same as a core, whereas ones with smaller depths don’t affect the unit’s net area. Therefore, the mortar bed should fill the indentation completely.
Some specifications dictate that facing bricks, hollow bricks and building bricks should have frogs of a specific size. Some experts also state that bricks should be laid with the frog on the top, whereas others say it should be bottom-first.
Why do UK Bricks have Frogs?
Brick frogs make sense from a practical point of view, both historically and in contemporary architecture. Here are a few reasons why brick frogs make sense:
- They saved brick manufacturers from using excess materials (i.e. they could make more bricks with the same amount of clay without the finished product being compromised).
- They make bricks lighter and easier to grip.
- There is additional space for mortar, resulting in a stronger brick bond.
- Indentations also provide a suitable spot to stamp the brick manufacturer’s name.
Hopefully, the above information about brick frogs has proven interesting and valuable to you in some way. If you are interested in finding high-quality bricks to use for a commercial project, look no further.