What the frog is
The frog is the shallow recess pressed into one face of many pressed and some handmade bricks. It makes the brick lighter, helps it fire evenly in the kiln and, often, carries the maker's name. Extruded wire-cut bricks usually have holes instead of a frog, and some bricks are solid with neither.
The short answer: frog up
For most loadbearing and facing work, bricks should be laid frog up and the frog filled with mortar. Filling the frog makes each brick act as a solid unit, gives a full bed for the next course, and adds to the strength and sound insulation of the wall. Brick manufacturers' guidance and structural design values generally assume the frog is filled.
Laying frog down leaves an air pocket under every brick. In a wall carrying load, that means less bearing area and a weaker wall than the design expected.
Why people lay frog down
Frog down uses less mortar and is quicker, which is why it turns up on rushed jobs. On a low garden wall or a non-loadbearing screen the difference in strength may not matter much, and some bricklayers will lay the top course frog down so the coping or capping sits on a flat surface. Those are exceptions, not the rule.
Double-frogged bricks
Some bricks have a frog on both faces. Here the question answers itself: the lower frog cannot be filled, so the aim is to fill the upper one fully and make sure the bed joint is solid. These bricks should be used where the specification allows for it.
Does it affect the look?
No. The frog is on the bed face, hidden inside the wall, so which way it faces makes no difference to the finished face. What does affect the look is the bond pattern, the joint thickness, the mortar colour and the finish on the pointing, and those are where good bricklaying shows.
How to tell after the event
You cannot see the frog in a finished wall, but on demolition or alteration work a wall laid frog down with empty frogs is obvious. In a new build, the best check is simply to ask your bricklayer how they are laying, and watch the first few courses.
How we lay brick
Our bricklaying is NVQ Level 2 qualified from Barnfield College, and we have been laying brick for more than 26 years across extensions, garden walls, chimneys and repairs. We lay frogged bricks frog up with the frog filled, unless the specification says otherwise, because that is what the wall is designed for. We are FMB members and fully insured, based in Bidwell, Dunstable.
It is a small detail, but small details like this are what separate a wall that lasts a century from one that needs work in ten years.
Other laying details that matter more than people think
The frog question is part of a wider point: how a brick is bedded matters as much as which brick is chosen. Full bed joints and fully filled perpendicular joints stop water tracking into the wall and give the wall its strength. Consistent joint thickness keeps courses level and bond lines true. Bricks should be clean and not saturated when laid, and work should be protected from rain and frost while the mortar is green.
The mortar itself should suit the brick and the exposure: a strong cement mix in a soft old brick causes cracking and spalling, while too weak a mix in an exposed wall erodes. Tooling the joints when the mortar is at the right stiffness gives a dense, weather-shedding finish.
None of this is visible in a photo of a finished wall, but all of it shows up over the years in how the wall weathers.
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Questions people ask
Is frog down wrong?
For loadbearing walls it is generally poor practice because it reduces bearing area. On some low non-loadbearing walls it is less critical.
Should the frog be filled?
Yes. Filling the frog with mortar is what gives a frog-up wall its full strength.
Which way up for the top course?
Some bricklayers lay the top course frog down to give a flat face under coping. Follow the specification.