Bricking being a rare occurrence in my DIY repertoire, I am curious about the various designs of the bricks. Why do some have holes going right through, and others just hollow 'frogs' on one side.
My builder bro in law tells me the frogs are supposed to face upwards, but could not give me the reason why. My 'common sense' view would have been that, were there to be any missed bits in the mortaring, or should cracks develop, frogs facing upwards would tend to collect water that might break up the wall if frozen while still wet. Also, laying 'frogs down' gives me a flat top to any little bits of bricking I do around the garden - though 'frogs up' would give a better key to any final layer of coping stones, so that might be the reason I suppose.
What is the reasoning behind frogs, their design and positioning while laying?
All frogs and holes are there for two reasons, firstly to create a bond, rather than just a flat surface, and secondly, to save clay during manufacture.
London bricks have one flat side and a hollow side, IME, the frog should face downwards, to save on mortar and to create a better bond, but that said, London bricks shouldn't be used for garden walls - they are too soft and will blow apart within a year or two due to frost / defrost cycles
I was told that frogs should not be used downwards, since all the force is carried by the edges, unless the frog is totally filled, which is very unlikely, especially if your aim is to save mortar. Also, if the edges spall badly for any reason, you can lose a lot of your load-bearing face. So frogs should be used upwards and completely filled. Fine to use frogs down for a top row where the upper face will be seen . My house is built entirely with bricks with no frogs or holes (from the now-defunct Leamington Brick Co. (stamped on them !)
For the bricks with holes, I have noticed the holes seem to be getting bigger. I think they are now made with the maximum allowable voids, which is specified in some BS or other.
I've got lots of ornamental garden brickwork all made out of secondhand stocks. No problems whatsoever. In over 20 years. And many much older than that garden walls round here - in varying states of repair, that's true - but then that applies to ones made of other bricks too.
I did post a few weeks (maybe months now!) ago - a detailed document form one of the brick making companies. In summary:
Absolutely always frog up - but if some nifty corner or something meeds to go the other way, fill the frog completely and carefully slide the brick off the trowel.
Many bricks 'grin' such that if they are laid not frog up, the face of the brick looks wrong.
Therefore, no saving in mortar.
AIUI, the frog was more to ensure that the brick fired more easily - i.e. the middle of the clay got hot enough. That to some extent explains why holes can have the same effect. Frogs might have saved clay and transport costs as well - but to the end user the increase in mortar usage probably offset that to a considerable extent.
I can see why London bricks should not be used for retaining walls, but for a free standing wall on a well drained base, there should not be any problem.
They built millions of houses with them, plus public buildings of all kinds, so I really don't think their durability is in doubt to the extent that was alleged.
My father always said frog up -- the other way up was for southern penny pinchers.
Recent information indicates that for energy saving reasons (and a slightly lower strength wall) that the frog should be down (thus creating insulating voids). For maximum strength when needed frog up.
I have not checked out thermal insulation qualites, but the info. I posted is clear on acoustic insulation - frog up. In fact, the document is crystal clear that only frog up is acceptable in almost all circumstances for a variety of reasons.
I replicate my post from 2 July this year:
Funny that - probably why Ibstock bother to produce Technical Information Sheet 25 - text below, with pictures if you go to the PDF itself. I have no idea whether three hole bricks are becoming more common but they certainly have not entirely replaced frogged bricks.
Laying ?frogged? bricks
British Standard Codes of Practice BS 5628-3 The Use of Masonry and BS
8000-3 Workmanship on Building Sites state that "Unless otherwise advised, lay single frog bricks with frog uppermost and double frogged with deeper frog uppermost. Fill all frogs with mortar....."
Bricks walls built with frogs down and unfilled are weaker and less resistant to sound transmission.
Advice should be sought as to whether bricks laid frog down are acceptable?.
Many bricklayers prefer to lay bricks frog down as they believe it to be a faster method and it uses less mortar. However the performance of the brickwork can be affected by insufficiently filled frogs.
Strength and stability
Compressive strength tests on frogged bricks have traditionally required them to be fully filled with mortar beforehand. The resulting figures are used by engineers in calculating the loads brickwork can support. Brickwork with unfilled frogs will fail at lower loads.
Sound Insulation
Changes to the Building Regulations for England and Wales in 2003 require dwellings to be constructed to new Standards so as to reduce the levels of transmission of sound between and within dwellings.
For solid masonry walls the resistance to airborne sound depends mainly on the mass per unit area of the wall (density).
To maximise this:-
o fill and seal all masonry joints with mortar. o use bricks that extend to the full thickness of the wall. o lay brick frog up to achieve required mass per unit area and avoid air paths.
Fixings to Brick Walls
Fixings to walls must be used with care so as not to disrupt the brickwork. The whole structure is less fragile when the voids are fully filled with mortar and there is maximum bonding of all surfaces.
Aesthetics
When laid correctly, the creases on the face of handmade or simulated handmade bricks form a ?smile?. Aesthetically it will look better if all the bricks are uniformly laid but will also help to shed water.
Exceptional circumstances
In very exceptional circumstances It is possible to lay bricks with the frog down and fully filled but it can be time consuming and suitable for particular details only i.e. if ?handed? bricks are not available for either side of an opening it may be possible to invert some on one side.
This may not be acceptable for some textured products.
To lay bricks with frogs down and filled, the trowel must be loaded with sufficient mortar and brick and trowel lowered into position.
For further help and advice contact the Technical Services Helpline on
LBC won't guarantee bricks used for garden walls, and most brickyards will tell you this if you ring and enquire....stock brick aren't made by LBC, even though they do have a slight frog, sometimes on both sides.
Lots of bricks are suitable for garden walls, almost all of them are not very porous, LBC bricks are like digestive biscuits
Have a look at houses built with them 20 - 30 years ago, almost all of them have had bricks replaced over the years due to blowing....the ones below DPC are usually mangled
LBC Flettons are fine if they're not saturated, i.e. in a house wall where the roof overhangs protect the brickwork, but if you use them in a coping or build a wall with an unprotected top they will disintegrate over time. They are cheap because the clay contains a certain amount of carbon which reduces the firing needed (as does the deep frog) but as this burns away during the firing it leaves a relatively porous core to the brick.
London stocks are a completely different sort of brick and generally much more durable.
Below DPC, I can understand. But elsewhere, as long as they are not in, or supporting damp ground, I don't think they are really any worse than most other facing bricks. Are they?
Garden walls have more stringent requirements for bricks, or you get much shorter life. They are exposed on both sides to wind and water, and they don't get any heat to dry them out. Consequently the same bricks used for a garden wall will have a much shorter life than when used to build a house.
When I did my bricklay course a few years ago, we were told that all the major house builders now insist their brikkies use frog down, as it saves 10% of the mortar. However, the external brick wall is not structural in modern houses, only having to support its own weight. The floors and roof all sit on the inner walls.
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember sm_jamieson saying something like:
The last few years I've been up the attics of many new-build houses and I've been taken aback at the sheer cheap 'n nastiness of the construction of houses that builders are charging an arm and leg for. It's almost a pleasure to go up into the loft of a traditionally built house.
Looking at them I doubt they've been selected in any way. Part of the rustic charm. ;-)
But it's common to have flank walls on houses built with the top bricks exposed - perhaps 'brick on edge' and they seem to survive ok. Although mine has stone capping.
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