Setting screed rails - Best approach to establishing screed rai

[FR114977]

Hi Tony/Folks

A DIYing first time patio layer here. I'm putting down a 90 sq m patio. I'm putting down a sand layering course on top of a good hard core sub base but at spots there are 10-20mm level differences in the sub base that I'm hoping post wacker will give a good surface to screed.
My question is what is your typical approach to establishing screed rails when you don't have an edge to work with? How do you then ensure the wacker does not interfere with the levels set for the rails?
As per the screed page I'm looking to screed every 1-2 metres for a distance of approx 4-5 metres,
(Great website, loads of useful info)

[Tony McC]

Why are you preparing a screeded bed? What is it you're laying?

[FR114977]

Apologies, 40 mm pre cast concrete flag stones

[FR114977]

Screed Rails: Just read MickG's and sonnyboys explanations in Tool and plant, should have looked before I leapt.
thanks

[lutonlagerlout]

what on earth is a sand layering course?

there is subbase (which never includes sand)
and there is a bedding layer ,which always includes cement

laying domestic patios on sand or building up levels in sand is a huge fail
LLL

[sy76uk]

I've laid literally hundreds of thousands of m2's of slabs on sand. Not because I've wanted to, because they were the spec's I had to work to. No big building firm will pay for anything laid on a sand/cement or full mortar bed when there are 1000's of meters on a job.

I agree with Tony (LLL) it never lasts and you'll spend the summer weeding the joint's which will have to be within a couple of mm and brushed in with kiln dried because mortar joint's don't work on a sand bed.

Your best bet is a full mortar bed.

If you have a well calibrated slab that is either textured or has a flat surface you'll be able to lay it on a screed bed as long as you keep an eye on the corners and top up the bed on any that are low.

Also screeding isn't as simple as it look's. If your rails aren't spot on giving you 1 gradient then the slabs will rock. Also keep an eye out for soft spot's in the screed.

[lutonlagerlout]

even the little 450 biscuits sy?

I always thought it was just the big council greys could legitimately be laid on sand alone?

LLL ???

[sy76uk]

By screed I meant sand and cement screed Tony but, yeah. I've laid 450 biscuits on sand. I've laid riven slab's on sand as well.

It's ridiculouse I know but when I turn up on site go into an office, look at a drawing and get given the spec's then I have no choice. I'd never recommend anyone lay them that way though.

I'll see it I can dig a few pictures out.

[sy76uk]

Here you go.
[img]https://farm8.staticflickr.com/7380....mg]26042011120 by sy76uk, on Flickr
450 perfeckta's laid on a screed bed. There was 1200m2 on that job. 2000m2 went in skips because they were the wrong shade. the firm that started the job went bust. Needless to say there were a fair few patio's laid around leicester and Nottingham after that job

[img]https://farm6.staticflickr.com/5319....mg]20120519_122146 by sy76uk, on Flickr

600x600 saxons laid on crushed glass.

[img]https://farm8.staticflickr.com/7404....mg]20120319_110229 by sy76uk, on Flickr

400x400 biscuits on dark sharp sand. (no cement in that)

Happens all the time.

[msh paving]

I have laid 450slabs on wacked, screeded sand, with a sand cement hauch, little 20m patios never had a problem, also on screed sand cement collected from concrete plant, not done it that way for year's but ican be done if done well. MSH



Edited By msh paving on 1400093425

[r896neo]

Both tobermore and acheson glover (who are the only real suppliers here in Northern ireland) recommend laying their 400x400 and 600x400 pressed flags on a compacted grit sand bed.

[sy76uk]

These were laid on a sharp sand bed and the house is only 7 years old. If they made an effort to mix a bit of cement in there then they would be as level as the day they were put down.

[img]https://farm8.staticflickr.com/7367....mg]IMG_1646 by sy76uk, on Flickr

[ilovesettsonmondays]

Where I work the council have seen sense and banned screening for slabs. Back to the old traditional method laying 63mm slabs individual.

[ilovesettsonmondays]

Screeding even ( I bloody pad predictive )

[Tony McC]

The 450mm 'biscuits' as you call them, and most other small element pavers are designed and intended to be laid on sand rather than mortar.

They are just a big form of block paving, created to bridge the perceived gap between pavers and flags.