best way to make polystyrene thickness with concrete screed

[karenandoz]

Hi all - hoping to get a little more help...
Have established that we can use 120mm EPS with a compression strength of 70 kPa, to keep down cost of insulating the new kitchen extension floor, to obtain u-value required. This allows us space to put in 80mm floating concrete screed above.

If you were me would you get 120mm EPS for around £26 (from specialist manufacturers, or get the bog standard sizes from building yard - this would have to be two layers - one of 100mm, plus one of 25mm. This would give us a screed depth of 75mm (min required by build regs).

The reason I'm asking is that by using two layers the price would only by £16 for the two combined, and multiplied up would save us a few quid, but I'm concerned that floor would not be as stable, as there is the potential for more movement, and the screed would end up being a fraction thinner to boot. Would we be wise to reinforce (traditional not flowing) screed at this thickness?

Sorry for long rambling question!

many thanks in advance

 

[karenandoz]

Also been reading other helpful posts, where some folks have got their knickers in a twizzle about 'load fatigue'...
We coulg get EPS of 100kPa (designed for commercial and heavily trafficked floors for about £30 a sheet - would this be a good cheaper middle ground without having to fork out even more for cellotex type stuff?

 

[jeds]

Once screed is thicker than about 65mm you won't notice any difference between that and 70 or 80mm. Personally, for the minimal extra cost, I would always have fibres added.

 

[karenandoz]

Thanks John - Have you or anyone else got thoughts on the EPS?

 

[karenandoz]

oh bejeeses - please help - the more I look in to this the more confused I get!!!!!
Trying to look up different compressive strengths of expanded, extruded, and PIR board - thought I had it then realised that some quote kPa to 1% and some to 10%......
And then I'm breaking out in a cold sweat about the weight of the american fridge freeze thats goin to stand in the corner!

Can anyone out there put my fragile female brain to rest and tell me to stop being so daft, and that 70 kPa Expanded Polystyrene absolutely great for the job (or even the 100kPa?)

Thank you in advance - any help appreiciated, as so hard to track down unbiased advice!

 

[jeds]

70kPa boards will support any domestic floor loads you are likely to put on them. All domestic floors - including the products sold to construct them - are designed to a British Standard floor loading of 1.5kN/m² plus a very generous safety factor. Your fridge will be safe. Just make sure the EPS is actually designed for use in floors and isn't some cheap rubbish.

 

[karenandoz]

Thanks again for your time - was really starting to pull my hair out on this one!
Ihave managed to chat to a very nice man from spring vale who set my mind at rest too - we just couldnt put a 1 tonne range on EPS 70 - would have to go up to 100 for that. s'ok though, cos we're not posh enough to have one of those anyway!
We have found out how important screed mixing is so that there are no weaknesses/inconsistencies - creating point load problems. Bizarrely only costs an extra £15 to get the pre mixed stuff dumped, rather than us mixing it all by hand after buying raw materials - so that was not a difficult decision!!!
cheers again, regards, karen

 

[^woody^]

For piece of mind you could reinforce the screed with chicken wire.

Fibres are not reinforcement, all they do is control early shrinkage

 

[Norcon]

Polystyrene is rubbish. I wouldn't take the gift of the stuff.
And also fibers IS reinforcement. We use it all the time. Even for shuttering.

 

[freddiemercurystwin]

Polystyrene is rubbish. I wouldn't take the gift of the stuff.

Rubbish, its use is widespread throughout the industry for domestic to civil's, its a sound and reliable construction material.

 

[noseall]

Polystyrene is rubbish. I wouldn't take the gift of the stuff.
And also fibers IS reinforcement. We use it all the time. Even for shuttering.

Oh Lordy!

 

[Norcon]

Polystyrene is rubbish. I wouldn't take the gift of the stuff.

Rubbish, its use is widespread throughout the industry for domestic to civil's, its a sound and reliable construction material.

Widespread amongst cowboy builders you mean.
Can't remember the last time I seen it used on site. Apart from packaging which is then sent to the tip.
Place for it imo.

 

[karenandoz]

always nice to start a little 'discussion'...

 

[jeds]

You should see it on site when the boys start waving their shoulder bags at each other.

 

[karenandoz]