Floor screed

[lutonlagerlout]

yes ,you can trowel 10 mm concrete,
but the industry standard is 3mm + - deviation over 3M,this is difficult to achieve with concrete thats why floor screed is used , to obtain a level and smooth finish

have a look here

cheers LLL

[sharpie]

Many thanks for the replies.

To answer a couple of questions, its a dining area off the kitchen and will ultimately be tiled.

The surface is currently concreete slab but I need insulation over this and then I understand polythene over that. So the screed will go on the polythene - correct?

So if I go for 3:1 sharp sand to cement, no plasticiser, I'll get 2 T of sand. How many bags of cement do I need?

I know its a dryish mix (what exactly does that mean?)
Somewhere I read that you need to hand/paddle mix rather than cement mixer. Is that correct (my arms are suddenly aching..)

Cheers!

[lutonlagerlout]

you definitely need a mixer for floor screed sharpie and for 2 tonne at 3:1 you want about 12 bags of opc
in one mix i would put about 1/3 of a bucket of clean water 4 shovels of screeding sand ,half a bag of cement then a further 6-7 shovels of screeding sand ,dont leave it mixing too long or the cement balls in the mix,it needs to be moist but =dry enough that it wont hold a shape in your hand if that makes sense
LLL

[sharpie]

No problem. I do have a mixer - just I thought i read that it needed paddle mixing - agreed that would not be a job I would look forward to.

Is screed sand the same as sharp sand?

[87-1235666499]

Sorry to throw in a curve ball but at 80mm thickness I don't really understand why you are not using a concrete mix incorporating 10mm pea gravel?

Oversand it to make it a bit easier to place a finish and a cube should work out something like this:

Cement 320kg
Sand 1036kg
Stone 740kg
Water 160 kg* Definitely use a water reducer aka plasticiser and if you do use a paddle mixer rather than tumble mixer you will be able to keep water content low, advisable to reduce shrinkage)

If you can get hold of some 6mm Polypropylene monofilament fibre, a 600g bag of this would be beneficial.

A cubic metre of this mix would be enough for 10 square metres at 100mm thickness so you will get about 12.5 square metres assuming your sub-base is nice and flat.

A primer using cement, water and SBR (or PVA failing that) brushed over the sub-base and not allowed to dry before the concrete is laid would be helpful.

Personally I would not put chicken wire in, it's tensile strength is not really high enough to make much of a contribution against cracking and tensile strength on a firm base won't be a big factor for your application.

Sorry to be a dissenting voice!

WOP

[DNgroundworks]

Cheers WOP, thats something similar to what i said, 10mm stone used in a conc mix at 80mm thickness should be fine.

Sharpie - you probably read that the self leveling screeds (polymer and sika based) need to be mixed with a paddle at slow speed, but i may be wrong!

I think you may struggle mixing a cement based/concrete/ semidry screed with a paddle.

[87-1235666499]

Sorry DN, you did indeed mention the stone, I must have missed that in my enthusiasm to hit the keyboard!

I also could have made it clearer that by paddle mixing I'm thinking of a forced action type of mixer with plough shares rather than the classic tumble style Belle which is better suited to wetter, slurry type mixes such as mortar.

They plough share mixers can be hired and make site mixing concrete an enormous amount easier as well as allowing lower slump mixes and thus a superior, better performing mix.

Have fun.
WOP

[lutonlagerlout]

guys !
floor screed does not have 10mm stones in it
this site is called paving expert,not do what you think
floor screed is 3:1 grit sand : cement
I am 100% on this
LLL

[DNgroundworks]

Maybe its misdescribed as a screed?

[msh paving]

As i stated on my first post screed is 3-1 fully backed up buy my learned LLL,you will never see a floor screeder using stone in it ,you cannot get a strong semidry screed with stone in it,chicken wire is common place in floor screeding,for the are in question a belle mixer will be fine, no point in forced action mixers or pan mixers its getting a bit much,take note off LLL posting on mixing screed MSH

[seanandruby]

A traditional screed floor consists of sand and cement 3:1 up to 8:1. you also have grano screed. Then you have lytag which is hard to get a good finish, it is lightweight, it is made from fly ash. For a kitchen i would go for traditional and maybe add some fibres, rather than mesh. 10 ml is a concrete base!!! I would'nt class it as screed, why pay for the stone when sand and cement does the job ???

[87-1235666499]

I absolutely agree with the points about "traditional" floor screeds, use of metal lathe, not using stone, etc., but in my experience these are, in general, for "topping" off rough bases to be carpeted, tiled, etc.

My thought was simply that for 16m2 at 80mm thick, which is pretty thick for a screed, it will be cheaper to use stone to bulk the mix out rather than use cement which is more expensive.

The use of stone per se does not increase the strength - in fact the converse is the case.

Still plenty of vigourous debate - by now the fella's probably decided to block pave it instead!

Best to all,
WOP

[lutonlagerlout]

when we get floors screeded the guys (irish and polish) turn up with their mixer/pump, they lay anything up to 500M2 a day and if there is a single pebble in the sand ,they pack up and go home
those pumps are expensive and stones wreck them

If you are screeding you use a straight edge and screed back and forward rather than tamp,to this end you need a small aggregate
10mm stone is sometimes used for finished concrete I.E. garage floors and petrol station forecourts
LLL

[Suggers]

Never known anyone screed with stone in it - wasn't screeding traditionaly a plasterer's job?

[msh paving]

Bit off topic for the site I know but I would appreciate some advice on internal floor screeding.

What mix of sand, cement (plasticiser?) should I use and how do I estimate quantities? - my floor is about 4x4m with a screed depth of about 80mm.
Is this within DIY scope and do I need any particular tools other than regular trowels, float etc?

Anyone know of a suitable diy guide here or elsewhere?

Many Thanks

why is everyone giving the advice to put stones in screed, floor screed is 3-1 sand and cement on housing work,
Myself,LLL,seanandruby and suggars have all stated the same

the reason for screed to form a close tight surface to allow carpet,tiles or laminate to floor finish to be laid level and flat this is not possble using a semidry concrete mix as the stone will flick out leaving the floor needing latex leveling compound,some one stated over sanding but whats the point in that gravel cost more than sand anyway so no saving
bad advice is worse than no advice at all

sorry to go on and on MSH