Blockwork Knowledge Needed Ta.

[charliegolf]

I need a few answers please, on a proposed blockwork job that I'm going to do.

I'm doing it, so "Don't do it" won't do

Going to build (on concrete) a blockwork trough 2x1x1 metres internal. Then I'm going to have it rendered internally (and top edge) with appropriate cement. Then I'm going to tile it with glass mosaics (appropriate adhesive)

It wil have a drain, but no filtration, chemicals or heating

It's called a Dip Tank. I'll do the 'Dipstick Tank' joke to save you typing time!

Q1. Will a properly bonded single skin 'trough' take the static pressure of 2 cu m water?
Q2. If 'yes' to that Q, will Celcon type blocks cut it and take the render and tiles?
Q3. Should I build the walls with the 'water resistant' mortar cement?
Q4. Any suggested brands for suitable cement and or tile adhesive?

Thanks for reading.

CG

 

[noseall]

Line it.

 

[Mr Chibs]

If I was having a stab at this, I'd be using heavy blocks, laid on their backs, perhaps some mesh roll, on the corners.

I wouldn't use lightweight blocks... they don't take render well either. You can add waterproofer to the mortar, but if you are rendering, probably not worth it.

If you were laying the slab, you could cast rebar in the slab, and use hollow blocks (don't know the name) threaded over these.

 

[tony1851]

A single-skin (100mm) x 1m high boundary wall would not survive wind force, so a single skin 1m deep water retaining wall certainly won't.
Without doing the figures, I'd suspect you'd need something like double skin, with a 100 cavity filled with concrete, and steel mesh wrapped round.

 

[^woody^]

Add ex-met to the bed joints to stiffen the walls.

2m3 of water is the same as 2 tonne of earth/ stone etc. I'd vote "yes" for single skin, but not in AAC blocks, use dense concrete instead as they are more thermally stable.

 

[^woody^]

A single-skin (100mm) x 1m high boundary wall would not survive wind force, so a single skin 1m deep water retaining wall certainly won't.
Without doing the figures, I'd suspect you'd need something like double skin, with a 100 cavity filled with concrete, and steel mesh wrapped round.

Apples and oranges.

The comparison is wrong. This will be a rigid rectangular structure, not a single wall, so the loading and reaction will be completely different.

 

[RonnyRaygun]

Apples and oranges.

The comparison is wrong. This will be a rigid rectangular structure, not a single wall, so the loading and reaction will be completely different.

Agreed. But no-one here knows how to do that calculation to prove it

 

[stuart45]

I've always done a raised pond in 9inch brickwork. When you put your hand between the liner and the brickwork you can feel the difference in pressure from the top to even a foot down. It's the depth of the water that causes the pressure, not the weight of the total area.

 

[charliegolf]

Thanks all. The thing will be on a slope, so some will be below ground, but most won't.

 

[charliegolf]

Line it.

With what Noseall?

 

[stuart45]

Look at the details for Koi ponds,as it's the same principle.

 

[^woody^]

Agreed. But no-one here knows how to do that calculation to prove it

I think it works

 

[noseall]

With what Noseall?

Pool liner.

 

[John D v2.0]

Interesting problem!
Water pressure does get huge, in laypersons terms 1m of water weighs 1kg/10N over each 10cm by 10cm square. So the bottom 10cm of your wall would have nearly 60kg/600N pushing it out. And the next 10cm has 50kg/500N (or so) etc.
Integrate it and you'll end up with force equivalent to 300kg/3000N on your wall. (I think)
Having a wall that can take that weight sideways is a big ask, even if it's concentrated towards the bottom of the wall.
The wall itself in dense concrete block would weigh around 2500N per linear metre I think.
So 500N outward force on 2500N of downward force doesn't sound stable to me when it's on a 100mm base

But I'm in no way a structural engineer!

 

[RonnyRaygun]

Interesting problem!
Water pressure does get huge, in laypersons terms 1m of water weighs 1kg/10N over each 10cm by 10cm square. So the bottom 10cm of your wall would have nearly 60kg/600N pushing it out. And the next 10cm has 50kg/500N (or so) etc.
Integrate it and you'll end up with force equivalent to 300kg/3000N on your wall. (I think)
Having a wall that can take that weight sideways is a big ask, even if it's concentrated towards the bottom of the wall.
The wall itself in dense concrete block would weigh around 2500N per linear metre I think.
So 500N outward force on 2500N of downward force doesn't sound stable to me when it's on a 100mm base

But I'm in no way a structural engineer!

Correct. I’m assuming the trough will be 2m long and not 2m high (wouldn’t really be a trough then).
So the worst design case is at the base of the 2m long side. However, as Woody says, the return walls will help immensely in stiffening the wall, and masonry has much higher flexural strength perpendicular to the bed joints than parallel to them. You will get a bit of two way action, but the majority of the load will be taken side to side. Engineering brick has considerably higher flexural strength than blockwork and a stronger mortar raises the strength still further.

There is guidance in BS8110 for two way spanning concrete slabs, but this assumes practically the same strength in both directions, so wouldn’t be appropriate to use those factors in the calculation.

I might just do a calc on it when I get to the office tomorrow, just out of interest.