Floating slab using EPS Styrofoam/Polyst instead of sand

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Floating slab using EPS Styrofoam/Polyst instead of sand

Postby PeterSek » Wed Jan 27, 2010 7:22 pm

We are planning to raise a floor in an existing townhouse by about 300mm to. This is to lower flooding impact during the rain seasons. However the concerns is that by adding 200 mm sand fill and 100 mm cement will substantially increase a load on existing foundations i.e. 17m x 4 m x 0.3 resulting in about 24 tons

Is it feasible to use EPS Styrofoam/Polystyrene (white stuff) instead of sand? I believe in Australia this building technique is called a ‘floating slab’ utilising Styrofoam wafers instead of sand with 150-300mm beams around the perimeter and 100mm channels in the middle every 2-4 meters. The slab is reinforced with 9mm mesh and rebars in perimeter tranches

eIn our case using EPS Styrofoam/Polystyrene will eliminate sand thus reduce overall weight from 24 to 8 tons

Are there any issues/known problems with using Styrofoam instead of sand?
Are Styrofoam wafers available in Thailand? Who sells these around Bangkok/Nonthaburi. So far the best price we got is for 60x120cm x 8” = 150 baht each which I believe is about 4 times the price of sand

I believe these companies sell/make Styrofoam but we did not have a chance to contact all of them yet
- IXL
- Asia Foam (Hat Yai)
- Thai Foam Group
- Foam Thai

Any comments and suggestions will be appreciated

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

Postby geordie » Thu Jan 28, 2010 12:08 am

why do you not cast in groundbeams then use pan peum (spelling could be wrong ) basically the concrete planks leaving a void under the floor it would make more sense to me another thing to consider with that amount of polystyrene is will it lift the floor in the event of a flood
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby developer3d » Thu Jan 28, 2010 4:05 pm

In Australia this method of construction is referred to as "waffle pod" - The name came from the fact that a finished slab would visually resemble a waffle from the underside - if you could see it.

The concept is based on living in a country where trades labour is expensive ( 3000 baht ish an hour ) and so commodity materials are cheap ( relative to trades labour ) so anything that can save time at the expense of low cost materials like polystyrene can represent a huge saving in construction costs - interestingly the exact opposite of building in asia.

The other benefits are that is really easy to calculate the exact quantity of concrete you will need as the footings are not dug in "variable" soil - ie the forms and pods provide exact measurements for the amount of concrete you need.

The finished slab is incredibly strong - stronger than regular slab construction, fast and where labour is expensive is much cheaper than regular construction ( a mute point in Thailand )

The pods are only there to support the concrete until it cures so in theory you can use any material, as long it can support the concrete - orginally pods where waxed paper boxes but they had trouble under the weight of men walking to pour the concrete and the concrete itself hence now they use polystrene pods.

I am building a house in thailand and am using this method of construction, couldn't find the pods here so I used the cheapest block I could find instead photo attached.

dscn0625.jpg


The only caution I would give you is that you mentioned "channels" every 2 - 4 Meters - that is incorrect, one the reasons that this construction method is stronger that a conventional raft slab is the channels are appx 1 m apart, there is reinforcing in between every pod. every 1M or so.

If I can give anyone here a piece of unsolicited advice about concrete it is this, buy yourself a concrete vibrator and give it you builder as a gift and insist he use it whenever pouring concreting, you can buy a small handheld vibrator for about 5000 baht, it will be the best 5000 baht you will ever spend.

Here is a link to a useful resource on waffle pods, lots of pics and other info.

http://www.wafflepod.com/engineer/index.php
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby developer3d » Thu Jan 28, 2010 4:21 pm

I thought I would add an image of a concrete vibrator just incase any readers are interested..
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby geordie » Thu Jan 28, 2010 10:39 pm

I have seen a very similar technique in the uk for large concrete roofs with smaller pods 18"-2ft usually underside is treated as a feature and looks ok if it supports the spans on public buildings it must be strong i would be a bit concerned in thailand because when it rains the ground turns to mush but looking at the way you have made the one in the picture if it moves it will be as one lump so in effect its a huge raft its definateley interesting so hope you will keep us updated on your build
Regarding the vibrator ??? i would be scared to let a thai loose with one unsupervised if he did not pop the shuttering ?? he would probably seperate the stone from the fines and if you gave him one he would more than likely sell it however used corectly a very useful peice of kit
my comments may be wrong but never deliberately
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby developer3d » Fri Jan 29, 2010 4:13 pm

haha yes i understand your comments about Thai trades I will bite my tongue : )

Actually one of the other benefits of waffle pods is they are very good for reactive clay soils.

In Adelaide Australia they have one of the most reactive clay soils in the world ie they soak up water and expand, and when they dry out they contract you can imagine what this does if the footing "beams" are in the ground that is reacting and "connected" with slab, one very fast way to open up cracks, the second is not using a vapour barrier.
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Re: Floating slab using EPS Styrofoam/Polyst instead of sand

Postby geordie » Fri Jan 29, 2010 6:05 pm

I feel justified after watching them destroy tool after tool on my build my favorite is drill bits
in the uk we have clear differences METAL bit WOOD bit MASONARY bit in thailand no problem whatever was in the drill when they borrowed it will be used for all three and if your masonary bit will not drill metal they put the drill on hammer hoping that will work


Regarding your build though at mum in laws bungalow the ground is almost liquid when it rains
so everyone builds their own little hill placing the house on top i initially thought the sole purpose was to stop water from floods only worked out later its more to force water away from the house creating a dry/ish island with the hope the house stays in BKK a new estate had the problems you described with the clay shrinking away from the houses resulting in severe cracking the houses where cheap BUT ???

It will be good to follow you build and see how it fares during monsoon as it is built on the ground not in it although the strength of the slab should guarantee survival i have heard that this is how to build on sand also ??
what are you doing for walls as there are no rebar hanging