Buying an excavator

dno67

Well-Known Member
They were banned in the US just like MDF.
One of the reasons was due to a few deaths from garage floor failure after a jack
went through the concrete surface.
One of the reasons l don't like them, is l can see a nice warm nesting spot for rodents resulting in a lot of beanbag balls overtime.
Dollar wise there a no brainer.
 

Albynsw

Well-Known Member
They were banned in the US just like MDF.
One of the reasons was due to a few deaths from garage floor failure after a jack
went through the concrete surface.
One of the reasons l don't like them, is l can see a nice warm nesting spot for rodents resulting in a lot of beanbag balls overtime.
Dollar wise there a no brainer.

If they are not done right you would have a problem but an 85 thick slab with SL82 mesh as standard that is only spanning 1100mm between ribs is pretty solid
I am using SL 92 mesh on mine
 

itlldoo

Well-Known Member
Raft Slab :

The steel reinforced raft slab is also commonly called an engineered slab. It consists of thick steel reinforced concrete slab integrated with steel reinforced concrete beams founded into the bearing soil for strength and support.

The classic approach is:

  1. Trenches about 450mm wide x 450mm deep are dug around the perimeter of external walls and under load bearing walls
  2. Reinforcement cages are laid in the trenches and reinforcement bars are also laid at this time, and turned up to pass above the top of the strip footing to accommodate later slab structure
  3. Concrete mix is poured into the trench to ground level with vertical reinforcement bars protruding up to be formed with the floor slab
  4. Moisture protection, termite protection, electrical conduit, drainage and sewerage pipes for bathrooms and kitchens are positioned
  5. Form work for the slab is then erected along the outer edges of the building footprint and on top of the cured concrete footings
  6. Steel reinforcement is laid for the slab
  7. Concrete is poured in one operation creating a slab that covers the entire floor area
Waffle Slabs

Waffle slabs are a reinforced concrete footing and slab system constructed on ground. They consist of a perimeter footing (edge beam) and a series of narrow internal beams (strip footings) at one meter nominal centers running each way. The whole footing and slab system is constructed on top of the ground.

The sides of the slab are made by edged Form-work, and polystyrene blocks (pods) create the formed voids between the strip footings. When viewed from underneath, the system of internal strip footings looks like a waffle – hence its called the Waffle Slab.

Waffle slabs achieve their strength by varying their height above ground. The higher the slab above ground – the deeper the beams. The deeper the beams – the more stiffness the system has.

While Waffle Slabs may be cheaper to build in some circumstances, they do not work very well in:

  • Soft ground conditions or where the soil can move.
  • Sloping sites. In simplistic terms – there is only their weight stopping them from sliding down a hill.
  • Cyclonic areas and high wind areas. High wind forces will engage enough of the waffle slab to resist the force but not without deflection of the slab. In very high Wind conditions it is possible that the waffle slab will lift and the walls crack.
Also these are some considerations in our opinion, for preferring an engineered raft slab

  1. If the ground around your house gets eroded or washed away, the area under a waffle slab is exposed. Exposed areas under the Waffle Slab can attract reptiles and other wildlife seeking Shelter.
  2. Ground preparation must be immaculate and kept that way for the life of the slab, by the owner/resident of the House. Care must be taken not to over water the ground near your house, build up the ground around your house, allow surface water to run towards your house (and under your house) or plant gardens next to your house, as this may all affect the slab.
  3. Raft slabs are cast against the ground whereas waffle slabs are cast onto polystyrene void former's and strips of concrete. An overloaded raft slab is less likely to crack because it is cast onto the ground.
 

dno67

Well-Known Member
This is just my opinion, those styrene blocks would be more likely to deform under compaction or degrade over time from contamination than packing sand.
Not having a go, just putting it out there.
I do enough of them and l know which l'd prefure if the extra expense is no issue.
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Albynsw

Well-Known Member
I don’t know how you guys do them down there but I have never done a pod slab that was not on piers unless it was laid straight on rock. I have built well over 100 houses using them and that is the standard detail here
The slab is essentially suspended on the piers and the pod is just their as a formwork void to save on concrete and to provide a compressible void in highly reactive soils to stop the slab from breaking which was the problem they were having back in the 80’s with raft slabs breaking their backs and the reason they came up with the waffle pod design
The price per m2 is the same here for raft or pods slabs so it is not price driven , maybe it is different down your way ?
Can’t see piers under yours, don’t they normally use piers down their?
My engineer designed the slab with both options but prefers the pod as it is a stiffer slab
I am not anty or pro either type but don’t see the negatives that people talk about apart from heresay
They are by far the most common slab poured for housing so I would say you would be hearing about them if there was as an issue
I see pod slabs V raft slab as the same as trusses V conventional pitched roofs
Not everyone likes the idea
 

dno67

Well-Known Member
The only time lve drilled piers is when the site has fill, the extra expense usually comes from having to dig your beams 100mm into good natural ground (usually clay) on the perimeter, sometimes we've gone down several feet over a large percentage of the slab area and thats an unseen extra expense when you have to fill with conc + the extra excavation. It's possible that better soil testing could overcome this to an extent.
Waffle down here without fill on the slab site is. Site cut, plumbing, level, 50mm rock then polly and away you go. With fill on the site it will be engineered with piers in the fill area.
 

itlldoo

Well-Known Member
yep i hear you Alby its just the way its done now, i don't mind one way or another ! but i have never owned a house on a slab. bearers and joists with hardwood floors for me.:cool:
 

Albynsw

Well-Known Member
That is interesting you don’t pier down there, piers are a standard detail here, I have 70 piers under mine all drilled to rock.
Itldoo, we still do a lot of hardwood floors but lay them on batterns fixed to the slab. Don’t often get asked for bearers and joists anymore, we usually do a suspended slab if it is too steep for a slab on ground.
I probably would not be so keen on a pod slab without piers either and would favour a raft in that situation

Cheers
 

Choook

Well-Known Member
That's a cracker of a view you're gunna have. :cool: I'm guessing lots of large glass on that side of the house?:)
 

billyj

Active Member
are they still using 15 or 20mpa conc in house slabs? just for shits and giggles and some idea of how poor new home construction is in this country, a footpath is min 32 mpa, and structural footing on a vicroads job is 40mpa, bridges etc generally 50mpa.
 

Albynsw

Well-Known Member
are they still using 15 or 20mpa conc in house slabs? just for shits and giggles and some idea of how poor new home construction is in this country, a footpath is min 32 mpa, and structural footing on a vicroads job is 40mpa, bridges etc generally 50mpa.

20 is the minimum I see specified with 25 the most common for slab on ground and 32 for suspended work usually.
I assume the 32 for footpaths are unreinforced? A number of councils specify that way so it is easier to cut and replace sections long term and like the 32mos as it handles the wear better.

I don’t necessarily agree that the strengths are under specified in domestic work, the engineer is not doing his job properly specifying more than what is required to do the job. Bricks are only about 7mpa so it is all relative to the overall construction. On a typical house slab the difference in cost to increase the strength from 20 to 32mpa is about $300 so cost is not really the issue.

Commercial and civil work is different and subject to different criteria of a much longer service life and subject to much bigger loads and abuse and corrosion resistance.
 

dno67

Well-Known Member
20 is the minimum I see specified with 25 the most common for slab on ground and 32 for suspended work usually.
I assume the 32 for footpaths are unreinforced? A number of councils specify that way so it is easier to cut and replace sections long term and like the 32mos as it handles the wear better.

I don’t necessarily agree that the strengths are under specified in domestic work, the engineer is not doing his job properly specifying more than what is required to do the job. Bricks are only about 7mpa so it is all relative to the overall construction. On a typical house slab the difference in cost to increase the strength from 20 to 32mpa is about $300 so cost is not really the issue.

Commercial and civil work is different and subject to different criteria of a much longer service life and subject to much bigger loads and abuse and corrosion resistance.

The trouble is modern 25mpa is only as good as 20 mpa was 30 years ago. IMO
The amount of chemicals and additives used in crete these days is mind numbing.
 

Albynsw

Well-Known Member
Been building a gabion wall around the front of the house in preparation to plant out the bank in spring

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The wall is 80 metres long and should have the last of the rock in on Monday, every rock ( nearly 70 tonnes of them) have been placed by hand.
I have a fair bit of shaping of batters to do so looking to buy a tilt bucket for the machine as they are not that expensive and will make it easier.
 
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