Screed tolerance

[Oddbod1]

Suggestions for screed tolerance over an area?

 

[rssteve]

What size is the room? What's the difference in level over what area. Are we talking 10mm over 5m or 10mm over 50cm?

 

[Oddbod1]

A room of around 25m to 30m2 (6x5m).

 

[rssteve]

And what distance are we talking over?

 

[Oddbod1]

I've just run one of those laser measurers around the room randomly and saw that the FFL screen is more or less the same in one side but then 10-14mm some 4-5m away.

 

[rssteve]

2-3mm per meter seems OK to me. Maybe there level was slightly out.

 

[^woody^]

15mm over a 2m straight edge generally.

But it can depend on what surface covering was intended/specified - less for vinyl or thin tiles, more for carpets and thick tiles

 

[endecotp]

I have seen a reference to a BRE guide stipulating 3mm over 3m as good practice.

 

[^woody^]

I have seen a reference to a BRE guide stipulating 3mm over 3m as good practice.

What guide? That's more accurate than a standard spirit level.

 

[endecotp]

I misremembered, it is 5mm over 3m.

I've not seen the guide itself because you have to buy it, but it is cited in a document from Kingspan about laying insulation boards on top of concrete slab (not screed). The text is:

In accordance with BRE good building guide 28 part 1 irregularities should not exceed 5mm when measured with a 3m straight edge​

See the bottom of page 9 of
http://www.kingspaninsulation.co.uk...2-97bb-5861799ab02a/Thermafloor-TF70-pdf.aspx

 

[stuart45]

NHBC guidelines used to be plus/minus 8mm in 2 metres, which is quite generous for a screed.

 

[Doggit]

I did a kitchen recently, found the highest point, drilled the floor in a 50cm square pattern, set screws in the rawl plugs, and then took a 6ft spirit level from the high point and leveled the kitchen up. Mixed the self leveling compound slightly wetter than recommneded and poured it, then floated it with a trowel to get it close to the screw head levels. It came out to with 6mm over the 6m length, and about 3mm over the 3m width - and I thought I'd scewed it up and should have done better.

 

[noseall]

No matter how good you are, even if you were a robot, it is impossible to get an unpredictable product perfect. The building trade is not or never will be perfect. Some OCD people will not accept this. Woody sounds about right with his tolerances but you will find some trades on each side of this accuracy scale, with the majority being on the wrong side.