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What concrete mix for slab with meshed UFH?


oranjeboom

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Hi All, 

 

I've managed to get a contractor quote me to pour and level our slab. It's a 'renoextension' jobbie (Extensions are up and old slab removed from current house) so all internal walls are up and I won't have any other brick/block walls going up on the new slab. Only major load will the the stairs.

 

Buildup:

 

  • Elevated A142 mesh with UFH cable tied
  • 300mm EPS Insulation
  • Compacted MOT T1

 

I therefore don't regard this as a structural slab. With the mesh in the slab, the mix will be a GEN1. I know others here like @JSHarris had C35 mix but that's only as they are true structural slabs, so I don't think I need to go that way. Would you agree?

 

 

Some people around here keep on ranting on about not forgetting to add fibres....

 

Did someone forget???:ph34r: looking at--> @Onoff

 

Also, do I still need to add fibres? £15 extra/m3  seems to be worth adding I guess.

 

I called the concrete company the aforementioned contractor uses and I was quoted  £2130 (inc) for 15m3  so not too bad seeing that includes the pump. Nice bit of profit for the contractor who says the job will take 2 days with the two of them with the total cost being £4000 (excluding fibres)! So labour charge comes to about £400each per day! Is that realistic? Said he'd come rounf the day before to set up lasers and mirrors etc, but I bet he'll end up doing that 1/2hr before concrete arrives!

 

I'm asking for a breakdown of his figures, but that does seem a bit high. I've called another national concrete firm and their price with fibres is £300 cheaper but then does not include the cost of a pump (which is likely to cost at least £300-£400 around here. So it's just his labour cost that seems excessive, imho. Guy seems to know his stuff at least and came recommended by a local architect and having found it difficult to find someone to pour the slab I may just have to bite the bullet.

 

OB

 

PS special offer at waitrose: https://www.mysupermarket.co.uk/tesco-price-comparison/Breakfast_Cereals/Kelloggs_Fruit_n_Fibre_500g.html

 

 

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Yes it was me that forgot the fibres! 

 

Sat there after having done the bathroom slab quite happy then found the bag of fibres! Thank God for the mesh. 

 

I am aiming to use them when I cast the wet room tray to the wall drain though.

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16 hours ago, oranjeboom said:

That would reduce the add-mix price to £2.69 per M3, but then the squirrels will be nibbling at the screed whilst it goes off. :D

 

16 hours ago, oranjeboom said:

 

Also, do I still need to add fibres? £15 extra/m3  seems to be worth adding I guess.

If it's near passive / low heat, then I believe @JSHarris has stated that it's not required. I'd tend to add them if it was a retro fit and the slab was going to run a bit hotter, but your on 300mm of eps so unless the house has no roof you should be fine. ;)

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28 minutes ago, Nickfromwales said:

That would reduce the add-mix price to £2.69 per M3, but then the squirrels will be nibbling at the screed whilst it goes off. :D

 

If it's near passive / low heat, then I believe @JSHarris has stated that it's not required. I'd tend to add them if it was a retro fit and the slab was going to run a bit hotter, but your on 300mm of eps so unless the house has no roof you should be fine. ;)

 

No heat loss calculations have been done. I have/will have 3G windows, EWI, MHVR and plenty loft insulation so would like to think it's going to be a lot better than today's BRs! And I have roof. A few more calls for other GEN1 prices. 

 

 

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Just now, Onoff said:

 

A man after my own heart! Done on the basis of it'll be so much better than it WAS! :)

Absolutely! And disputing the crap my architect was suggesting and raising of eyebrows at the BR! Has all meant I am almost at yr 4, rather than living in an expensive, inefficient box! I may be wifeless by the time the place is ready though!

 

@Nickfromwales I was down your way last week and sampled just a few local brews (can't recollect them, one had a ref dragon on the label). But I haven't tried the above one. Next time I am dragged down to visit the MIL!

 

Phoning round I came to around the same Gen1 concrete price (£2570ish inc) which includes the pump hire (2days). So the labour side of it is then £1400ish so £350/day for both guys. Still seems steep, but that's mostly due to me not having anyone paid on site for a while and also due to being a typical stingey tight-arse (dutch) git. And the floor is one of the things I don't want to risk doing myself!

 

So if I don't go for the mother's milk option above and do decide to go for fibres.

 

Looks like I can get 900gm bags of fibre on fleabay for about £8/m3. How practical is it to ask the delivery guy to add this to the mixer?

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9 hours ago, oranjeboom said:

 

No heat loss calculations have been done. I have/will have 3G windows, EWI, MHVR and plenty loft insulation so would like to think it's going to be a lot better than today's BRs! And I have roof. A few more calls for other GEN1 prices. 

 

 

 

It doesn't take a lot to cut down on heat loss when you get into it does it? As a reminder to us in the cheap "refurbishment" seats as to the benefits of air tightness...it KEEPS on amazing ME the "lossiness" of traditional construction.

 

I just dug out the reasonably well done floor to wall edge in the bathroom to fit the wall drain. Bear in mind I've been living with this corner for a good while now, albeit unfinished so have obviously got used to the room being warm 'ish. This corner has no insulation on except a bit of foam/EPS along the bottom near the floor (which is done well). Cutting into this DPM and peeling back, Christ almighty the DRAUGHT you can feel. No "gaps" that you can see per se so must be thru the joints, DPC etc. Even adding a coat of liquid DPM has noticeably cut the chill down:

 

SAM_5807

 

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