Brickwork.
- Thread starter conny
- Start date
No, always upwards in load bearing walls as the whole frog should be filled with mortar to give the design compressive strength.
Often the frogs are laid downwards in non load bearing walls as it saves on mortar and strength isn’t an issue. Still not necessarily good practice though.
Often the frogs are laid downwards in non load bearing walls as it saves on mortar and strength isn’t an issue. Still not necessarily good practice though.
Is it for strength though?
That's the standatd line, but are there any calcs to prove it. I've never seen the evidence.
If it is the case that all frogs should be filled for strength, why aren't the same rules applied to bricks with through circular or slit frogs or perforations?
What is proven though, is that voids in frog-down brickwork can retain water leading to increased efflorescence and or frost damage.
I don't even think the saving on mortar is true either, as you need to lay a massive bed to stop frog-down bricks sinking and tipping all over the place.
Good question. I would think ideally any voids should be filled up in any bricks to ensure maximum strength of the masonry panel.
I’d also expect that any testing carried out in labs to give the compressive strength of a panel constructed with a particular strength brick would have higher level quality control than is ever found on a building site.
It’s interesting that the type of frog or void is never considered in the British Standard tables - just the compressive strength of the unit itself. And I don’t know if the frogs or voids are filled with mortar when the compressive strength of the unit itself (not the masonry panel) is tested…
The tables themselves are all created through empirical lab testing so not sure any actual calcs would be available.
Maybe the above are the reasons why we work to a material factor of safety of 3.5 in addition to the 1.4 and 1.6 for dead and imposed loads. With all those factors of safety it makes me wonder how a masonry panel ever fails
Frog down is approximately 1/3rd weaker than frog up. I have seen a wall buckle whilst being built (very quickly) frog down.
There you are then. With the huge factors of safety there still shouldn’t be any issues!
(If you can stop it buckling during construction
)
Last edited:
The London Brick Company did some tests back in the early 70's and their results were that up to 2 stories in height frog down could be used with a 30% saving in mortar.
The early 70's saw a big swing to using subbies on site, and the Fletton was the most common brick around then. Most of the lads on the cards laid them frog up, whereas subbies frog down. This caused some serious arguments with the CoW's on site, until LBC did their tests.
The frog up or down argument especially applies to the Fletton because of the deep frogs, but anyone who has laid loads of them on price knows that frog down is faster.
In the USA frog down is considered the correct method.
The early 70's saw a big swing to using subbies on site, and the Fletton was the most common brick around then. Most of the lads on the cards laid them frog up, whereas subbies frog down. This caused some serious arguments with the CoW's on site, until LBC did their tests.
The frog up or down argument especially applies to the Fletton because of the deep frogs, but anyone who has laid loads of them on price knows that frog down is faster.
In the USA frog down is considered the correct method.
If this is the case, don't they have issues when trying to fix to the masonry with expansion bolts or resin anchors?
This is another reason why frog up is preferable as I know from experience it's a real pain when you drill into a brick and when you pump in the resin you end up filling up a huge void. I know you can get the sleeves, but it's not ideal, and expansion fixings don't work at all. Also big problems with hammer fixings or frame fixings.
Last edited:
I've seen a solid block wall buckle while being built, no frogs.
So what about bricks with the holes, slots or perforations then? Are they filled? Should they be filled?
They don't take fixings well either if unfilled.
IIRC, no LBCs have/had a weathering face, so that must surely mean they are intended to be laid either way up.
They don't take fixings well either if unfilled.
IIRC, no LBCs have/had a weathering face, so that must surely mean they are intended to be laid either way up.
I've seen loads of walls going up in Flettons frog down quickly without any problems, but have seen a few built in wet Warnham bricks and similar start to squeeze out the pug and bend. Warnhams were double frogged, so would always be frog up and down.
Always wrong then!
Exactly - it's always a PITA as you invariably end up hitting an unfilled void.
All the bricks on my exterior walls (no cavity) have frogs facing downwards, as do all the other houses around us (built between 1945 and 1947). No cracked bricks and many have had loft conversions so the load is now greater.
The thinking is that any water making its way past the mortar can’t find its way into a frog, freeze and then crack.
The thinking is that any water making its way past the mortar can’t find its way into a frog, freeze and then crack.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
