Floating slab using EPS Styrofoam/Polyst instead of sand

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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby developer3d » Sun Oct 31, 2010 10:35 pm

Dear Maseratimartin,

These types of discussions are exactly why I have pulled away from commenting.

1, Your 100% right. A waffle slab is not the same as Estrich.

Why ?

To start with Estrich is not a "slab" its a non structural bed of mortar that is laided down over the top of the slab ( The Estrich layer often contains radiant heating pipes )

At less than 5cm thick as you say its non structural ( hence the cracking issue - nothing structural would ever be 5cm thick nor should it ever crack if the foam underlay fails ) and yes in this case the foam is designed to provide insulative qualities often in support of the radiant heating.

This image shows Estrich being done with self leveling mortar but it can also be screed laid.

Image

2, You also asses the solution as

Maseratimartin wrote:The waffel design concrete slab is in my opinion a cheap chary version....the waffel inserts are only to safe concrete.


Whilst it is true that these types of slabs are fast to construct and conserve considerable concrete when compared to a monolithic slab of similar thickness ( mine are usually 300MM thick ) this statement shows you don't understand the fundamentals of engineering involved.

The slab is designed to be extremely stiff - the stiffness is created by the steel in the "beams" that are formed at 1m x1m spacings around the voids - not the concrete above the void forms - ( concrete provides compressive strength and steel the torsional strength ). The beams have reinforcing bar running at the bottom and the top of the beam.

So you have 300mm steel reinforced concrete beams running in 2 directions at 1m x 1m spacings.

Picture what that would look like if you took off the 85 mm layer over the top of the voids, crisscrosses concrete beams 300mm deep at 1M spacings.

And your asking who would "sign off" of that ?

This is one of the strongest slab designs in the world !

The reason the waffle style slab was developed was to create a slab that was "stiff" enough to provide a slab solution suited to the highly reactive clay based soils of Southern Australia - for anyone following highly reactive means when the clay gets wet and then dry then wet again it "moves" cracking regular "embedded" footing solutions through differential movement issues.

The solution proved so versatile that it was soon adopted around the World for sites with a variety of differential settling issues, high seismic activity and many other issues.

It is not an ideal solution for every site ( but there isnt one ) I am however a big fan of this method where you are building on "compacted " fill with a high clay based content as we often see in Thailand in reclaimed rice paddy where you can expect differential settlement.
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby otis-a » Mon Nov 01, 2010 7:18 am

excellent discussion. I aced my soils class but applied the knowledge gained on pore pressure to well drilling and development. Feel like i just had a refresher class!
where to park dog when in town? A barking lot... :-)))
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby Maseratimartin » Sat Nov 06, 2010 8:54 am

Ok sorry that I took a floating slab for a floating screed (Estrich), but when we look at the text what opened the topic it was about raising a floor inside a house what is actually in the direction floating screed.
In this case a good quality styrofoam is necessary as it supports the floating screed...developer mentioned it already...

Then we drifted to outside slabs...waffel pods/slabs....and there came the question about usage in cold climates...
I will now not comment any other systems anymore....regarding to cold climates....just have a look at this link: http://www.3s-selbstbau-berlin.de/bodenplatte.htm
The "Thalhammer" slab is the normal way to construct the base of a house in Germany...usually the foundation ring what will be covered with styrofoam is about 80cm deep.
Usually the technical descrition asks for grounded to natural grown ground....so in case of fillings it has to be deeper...
In colder areas the depth will be increased...example: My last project in Czech...temperatures in winter normal to -30degrees...the Foundation ring was required to be 1,20m deep!
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby geordie » Sun Nov 07, 2010 6:17 am

standard for uk footings is commonly reffered to as a meter spit
a spit being a digging spade used for trenching with a blade length of 10"
any sighn of wetness from overnight rain and you will be on the shovel again taking it deeper
upset the building inspector and you will be digging it deeper
my comments may be wrong but never deliberately
If it aint broke, dont fix it
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby thaicbr » Fri Jan 18, 2013 1:57 pm

Developer... how is your build doing... any pictures etc.. i am thinking about using the interlocking bricks on a cabin build..Thanks Allan
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby Roger Ramjet » Fri Jan 18, 2013 4:18 pm

thaicbr,
Developer3d has not posted here for over 2 years unfortunately. He was a wealth of knowledge and will be sorely missed.
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby MGV12 » Fri Jan 18, 2013 4:59 pm

Roger Ramjet wrote:thaicbr,
Developer3d has not posted here for over 2 years unfortunately. He was a wealth of knowledge and will be sorely missed.


He did log in a couple of weeks back ... so you never know

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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby thaicbr » Fri Jan 18, 2013 8:52 pm

well i can hope. as i am finding the interlocking bricks to be intriguing.
I have found one supplier in my area. But amazingly they do not deliver so still looking.. Nakhon Pathom area.
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby Mike Judd » Mon Dec 09, 2013 9:32 am

Some of the various Raft Slab foundations that I have seen in construction manuals have that Waffle shape in the slab part itself, which is obviously to save concrete but to still have the strength. The whole point of the design is to have a raft that is so strong in itself with strengthening beams where the loads are heaviest that if there is some small settlement, it is minimal and even. I do have some practical experience although in another field, where I built a 6mt square platform 4 mts high for a drilling rig out of scaffolding on tidal mud, it had to take tons of load. I first tried putting the scaffold legs down into the mud hoping they would hit rock, but at 5mts and still going I gave that idea away. So I then laid out 50m.m. thick x 240m.m. wide scaffold planks 1 mt apart over the whole base, on those went 6 mt scaffold tubes at right angles, then the legs were fixed to those at the required height at the top with the surplus down in the mud. The whole structure was braced in a 1 mt grid but I was still surprised afterwards at low tide to see that the supporting planks were still just sitting there with all the load on it. My point is that it takes a lot to displace soft ground even mud if the load has a wide strong support.( Another geriatric reminiscent comment)
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby geordie » Fri Dec 13, 2013 1:56 pm

thaicbr wrote:well i can hope. as i am finding the interlocking bricks to be intriguing.
I have found one supplier in my area. But amazingly they do not deliver so still looking.. Nakhon Pathom area.


I would be careful about interlocking bricks there was a discussion some time ago it was actually about a school roof but interlocking bricks were used I think it was Fang anyway the bricks did not in my opinion save any time or make the building more secure if anything it complicated things as the bricks all had to be manually de burred before laying then grouted with cement it looked a messy process then they had to reinforce the walls by adding brick colums (probably lack of experience caused this problem ) recently I have seen in several places locally a red clay brick European style / size they look quite well made although I have not found a source for them they are popping up around Sukhumvit and Thanyaburi so if its for appearance I would suggest them as an alternative
another couple of negative,s on the interlocking bricks is corners are log cabin style toothed out both directions and even more of a downer is unless you render the insides there is a lot of daylight visible
Those comments from a friend who has purchased a bungalow built with them near Chang Rai
my comments may be wrong but never deliberately
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby qon » Tue Jul 29, 2014 3:36 pm

Hi

Late but may be helpful, here are some pictures of such a slab. Please note TH have many EPS/foam producers, but they vary in price/volume as most are wholesalers. As it has been said by someone here, the foam is for form work only, so low density foam is ok as long as it can handle the concrete weigh. The old way is to use clay-y sand fill, compact it then cut channels (that's why you need a clay-y sand so it will not collapse), cover it with plastic to achieve similar form work; but time = money. Take note of the 3bar mesh (front left, laying on top) that is what we use for trenches, 2 of. This is an AU job, note of step down for garage on the left and front. Could do the same for wet areas in Asia. Elevated slab > 50 cms is a completely new ball game, needing columns + slab which can be tie in to the beams or 'float' on beams.

I am not sure where to post this reference but check this website out, full of data and calculation infos http://www.totalconstructionhelp.com/momenti.html
Attachments
Slab.jpg
Foam-form.jpg
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby Andyfteeze » Sat Sep 13, 2014 11:25 pm

Great read guys, keep it ip. I too am tossing around how to do down stairs. My preference is for columns because the locals have experience this way and i can see ways of doing it well.
Advantages of concrete on ground. The ground acts like a great heatsink so the slab stays cooler when not subjected to hot sun. Columns can be incorporated. Inside a well insulated house this works very well.
Advantages of waffle pods. Concrete is insulated from the bottom. Again in a well insulated house with air con it works very well.
As for waffle pods, we had massive issues at the start with cracking of slabs. It turns put, 100mm wasnt enough. So 150mm became the norm. Please correct me if i am wrong on this. But the issues disappeared .
I built in melbourne over a filled quarry. I used 250mm thick floating slab. After 10 yrs, minimal issues. Did i mention my Italian background, lol
Decisions decisions
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