Garden wall advice.

Charlie George · 22 Jan 2020

^woody^ said:
Not like that it isn't - that's the numpty way. That gives a very slender height to length ratio which makes each block more prone to cracking.
If blocks are to be laid flat, then they should be laid one on top of the other for two courses, and then bonded and so on.

But even so there is no advantage in laying blocks flat - its harder, takes more time and uses more mortar.

So how would you build Poes wall in concrete block? the way i suggested is the way every liftshaft/stairwell and countless retaining walls i have built in 37 years has been built(as specified). As for saying its harder, for a novice it would be easier to build the way i said, and using extra mortar at least there will be no voids in wall or ties needed

One example of many built by numpties

tony1851 · 22 Jan 2020

Poe said:
From an engineering point of view or building regs point of view?

Poe.

What's the difference?

Poe · 22 Jan 2020

Sorry I was asking if it was being implied building regs state walls over 2m require planning or because as the wall gets taller off the foundation it would require a more substantial design.
Just trying to understand what was being suggested.
I was around the in-laws today and the neighbour is having a wall retaining wall built which is 2m high and the lower section (retaining) is blocks laid flat and there upwards is normal two skin construction.
It was getting dark and I had distractions but it may have been slightly taller.
So a compromise of what woodie and Charlie are discussing.
Poe.

^woody^ · 22 Jan 2020

Charlie George said:
So how would you build Poes wall in concrete block? the way i suggested is the way every liftshaft/stairwell and countless retaining walls i have built in 37 years has been built(as specified). As for saying its harder, for a novice it would be easier to build the way i said, and using extra mortar at least there will be no voids in wall or ties needed

One example of many built by numpties

Well even after 37 years is never too late to do things right. Same for crap specifiers who tend not to know much about brick or blockwork.

Anyway, the thing is with lift shafts, they tend not to move because otherwise the lift gets stuck. But the principle is still the same. The ratio risks cracking, that's why the OP should not do that on his wall - which certainly will move.

So yes there is no advantage, but many disadvantages. And if you are on price work, you're actually earning less than you could, but that's up to you.

Charlie George · 22 Jan 2020

Ok woody i'll just carry on as normal.

^woody^ said:
the thing is with lift shafts, they tend not to move because otherwise the lift gets stuck

So every other wall built this way will move,how do the blocks know ?
And regards price we get £2 per block for building block flat.

tony1851 · 22 Jan 2020

^woody^ said:
Well even after 37 years is never too late to do things right. Same for crap specifiers who tend not to know much about brick or blockwork.

Anyway, the thing is with lift shafts, they tend not to move because otherwise the lift gets stuck. But the principle is still the same. The ratio risks cracking, that's why the OP should not do that on his wall - which certainly will move.

So yes there is no advantage, but many disadvantages. And if you are on price work, you're actually earning less than you could, but that's up to you.

You overlook one point. Technically, a 7N block laid flat has only about 50% of the compressive strength than it would if it was laid upright.
For a heavily-loaded structure, I agree it is structurally best if the blocks are laid upright (fewer mortar joints make for better load-bearing capacity).
But for a retaining wall or free-standing wall, the main force is horizontal (earth in one instance and wind in the other). For these, compresssive strength is not so significant and the blocks are best laid flat. Two 7N blocks laid upright side-by-side are not as good at resisting a horizontal force as 2 or 3 blocks laid flat.

Mobo_14 · 22 Jan 2020

Hey guys interesting topic, so just to clarify a wall built bonded in this manor has more compressive strength than a single course of block on flat half bonded??

tony1851 · 22 Jan 2020

Mobo_14 said:
Hey guys interesting topic, so just to clarify a wall built bonded in this manor has more compressive strength than a single course of block on flat half bonded??

For an equivalent wall thickness, blocks laid upright form a wall approx twice as strong in compression as a wall with blocks laid flat (other things being equal and provided the wall isn't too slender, when different factors come into play).

Charlie George · 22 Jan 2020

Tony thanks for info, Woody if you drove a car at a block wall which type would you choose flat or stretcher ?

and you can't choose thermalite.

tony1851 · 22 Jan 2020

Never mind driving it at a wall, he wouldn't know how to drive it unless it was a pedal car.

^woody^ · 23 Jan 2020

tony1851 said:
You overlook one point. Technically, a 7N block laid flat has only about 50% of the compressive strength than it would if it was laid upright.
For a heavily-loaded structure, I agree it is structurally best if the blocks are laid upright (fewer mortar joints make for better load-bearing capacity).
But for a retaining wall or free-standing wall, the main force is horizontal (earth in one instance and wind in the other). For these, compresssive strength is not so significant and the blocks are best laid flat. Two 7N blocks laid upright side-by-side are not as good at resisting a horizontal force as 2 or 3 blocks laid flat.

You keep mentioning "not as good as" and "less efficient", but the fact is that if the blocks are laid vertically they will be more than sufficient to resist the loads you mention. So there is no advantage at all by laying them flat - even if as you say (although I have not checked) that there may be some marginal greater load resistance.

So that being said, the risk is of vertical movement, and for the OP, potentially ease, speed and cost. These are the important factors and which need consideration.

Bear in mind the OP is working out of a garden not a text book of theoretical formulae.

^woody^ · 23 Jan 2020

Charlie George said:
Tony thanks for info, Woody if you drove a car at a block wall which type would you choose flat or stretcher ? and you can't choose thermalite.

I'd delegate it to Tony to drive, although I doubt he'd get out of first gear after studying the Highway Code.

tony1851 · 23 Jan 2020

^woody^ said:
You keep mentioning "not as good as" and "less efficient", but the fact is that if the blocks are laid vertically they will be more than sufficient to resist the loads you mention.

OK, lets look at a few numbers:

Suppose we have two free-standing walls, wall 'A' built the Woody way with blocks laid vertically, and wall 'B' built the proper way with blocks laid flat (both walls are the same thickness, 200mm).
The horizontal wind force applies a bending moment 'M' to the wall. The wall therefore needs to have a moment of resistance ('MR') such that
MR > M.

The MR is proportional to Z, which you will know is the section modulus of the wall.
For any given section, Z = bd²/6.
With the Woody wall, the metal ties will be insufficient to effectively make the two skins as one, so each skin makes a separate contribution to MR.
Therefore for 1m length of Woody wall, the MR = 2 x [1 x 0.1²/6] = 0.003 units,
while for the correct wall, MR = 1 x 0.2²/6 = 0.006 units.

So in terms of resisting wind load, the blocks laid flat are twice as efficient as blocks laid upright QED.

^woody^ · 23 Jan 2020

tony1851 said:
With the Woody wall, the metal ties will be insufficient to effectively make the two skins as one,

Lol, who said anything, anywhere about metal ties?

Remind me, how does English garden wall bond work as a concept? Or how does a roll of exmet affect the calcs?

Sorry, I can't let you drive that car unless there's L plates on it.

tony1851 · 23 Jan 2020

Oh, come on, Woody; you know as well as I that it's all to do with the molecules! Here's the mathematical proof:

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Garden wall advice.

Charlie George

tony1851

Poe

^woody^

Charlie George

tony1851

Mobo_14

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