Floor screed in extension - Advice needed

[IanO]

Hi
I have a new ground floor extension (three rooms over about 38 sq m). The existing house has concrete floors, as does the extension, but I need to level / screed the difference which is 16mm. The new floor is quite consistent, ie no major bumps or pits, but 16mm lower than the old build.

Please could someone advise as to the best screed / levelling method. I know some on the forum sell screeds - but 16mm is a lot for self-levelling and not enough for traditional mortar.

Before you ask, yes I am the silly DIY b****r who designed this!

Any advice would be appreciated.

BTW I intend to lay solid oak flooring on top (with a membrane, etc) There are no pipes / heating issues.

Thank you

Ian
Epsom Downs.

[matt h]

why not cover the floor area with ordinary flooring sheeting, and then fix your oak to that... i did just that in my living room and it looks great;)

[lutonlagerlout]

ian be very very very flipping careful with oak flooring on concrete floors
i have installed 5 in the last 2 years and 3 have lifted

the oak needs to be taken out of the boxes and acclimatised for at least 1 week
also you must have a 25 mm MINIMUM gap around the sides
believe me this stuff can expand like nothing i have ever seen

my dinning room was like an inverse trampoline for a good while
hope this helps ya
LLL

[IanO]

Matt

Thanks, but what do you mean by 'ordinary flooring sheeting'? If you mean the mineral board, I thought this might compress too much at a depth of 16mm, or are you suggesting something else?

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LLL

Thank you for the warning, I intended to lay the boards in the rooms for a couple of weeks, but had thought 10mm gap would be enough - I'll increase it.

I was considering putting battens down, as I believe 16mm is just about enough - so for part at least this couldresolve the concrete / oak issue. However, I am still keen to explore the screed.
------

All - if anyone has knowledge of self-levelling material that can level to a depth of 16mm, please let me know.

Thank you

Ian.

[Tony McC]

Normally, for anything over 12mm, I'd use a granolithic mortar rather than a self-levelling product. You could, I suppose, use a 12mm grano build-up and then go for a 4mm S-L screed on top of that, if you wanted to have that smooth, accurate(ish) finish.

[IanO]

Tony

Thank you for the suggestion / advice. Two brief questions based on the main website under 'granolithic mortar'.

1. Sand - presumably 'sharp' sand?

2. First paragraph states "..as thin as 6mm in certain conditions" but later states "..should be at least 20mm thick" - will I be okay at 16mm?

As always, thank you for your help and this forum.

Regards

Ian.

[lutonlagerlout]

before you batten it or put your lovely oak boards anywhere near it make sure as much moisture as possible has gone out of the floor
our ex cleaner the lovely magda from EE mopped the floor with a wet mop and it lifted a day later
its is very unforgiving
TBH Ian i wouldnt recommend natural wood for a floor,it marks easily,it gets dents knocks atc atc
we have engineered flooring up stairs its 15 mm thick and it lasts a lot better than wood only
plus its about the same money but easier to install
i have a good fella for real wood flooring if you havent got yours yet,PM if you need his number
but as i said i would go for engineered every time now
cheers LLL

[simeonronacrete]

Easy, simple and very straightforward. Lay a trowel-applied bonded cement screed using a mix of cement, medium sharp sand, Ronafix and water.

1. prepare the concrete surface by mechanically abrasion using, for example, a scabbler, Von Arx plane. You can hire these. You need to take off loose material, laitence (friable cement film), any oil, contamination to make sure the screed bonds to the concrete.
2. clean, eg sweep or vacuum to remove dust
3. wash with clean drinking quality water to soak up any porosity and leave the surface damp
4. mix a primer of Ronafix (liquid) and cement, 1:1 in a bucket. For 38m2 you'll need 10 litres of Ronafix and 10 kg of cement for this primer.
5. apply the primer on to the wet concrete with a brush, roller or broom. Don't spread it too thin
6. you must apply the screed before the primer dries
7. mix the screed by hand or using a drill and paddle mixer, not a free fall "cement mixer". Dry mix the cement and dry sand (1:2 by volume), dilute the Ronafix with water (1:1) and add enough of the diluted Ronafix to the cement and sand to give a semi-dry screeding mortar
8. trowel the screed onto the wet primer using normal screeding tools and techniques
9. once laid protect it from too rapid drying with a sheet of polythene; if it dries too quickly - eg from a breeze or sun - it will crack
10. at 20oC you can walk on it after 1 day; allow longer at lower temperatures, maybe 2-3 days. But if it's hard, it's OK to walk on with flat shoes (not your stilettos'!)

As to how much Ronafix you'll need:

10 litres for the bonding primer
55 litres for the screed

Ronafix is stocked at Brett Building Materials, W T Burdens, some Travis Perkins and Buildbase. Or call us on 01279 638 700 and ask for Sales.

If you want technical help call the same number and ask for Technical Support.

Thousands of people have used Ronafix for floor screeds since 1969, so you're in good company!

[IanO]

Simeon

Thank you for the information on your product. I had in fact spoken to someone in your company (Danny?) and downloaded the product sheet.

It seems the perfect solution, but at nearly 8 times the price of petrol, it is very expensive. Especially as I would need in excess of 60 litres.

Given the price I need to weigh up my options (rather limited, admittedly!).

Regards

Ian.

[Dave_L]

Go for it Ian!

[IanO]

Tony

I am going to take your advice and use Grano for this job. Please could you advice / confirm quantities.

The area is 38 sq m. Depth is 16mm (pretty consistent) therefore, I need 0.608 sq m by volume.

Based on your Grano web page the ratios are therefore, 67%+11%+22%, but how is this translated into volume by weight? My estimates are: 400kg + 67kg + 133kg (plus a margin 10/15%?) or am I being daft?

I have looked at your calculators but I don't think any of them are quite right for this job - if one is, please advice and I'll do the sums.

Thank you for your help.

Ian.