Screed to concrete floor

[PJ]

Anyone know what mix should be used for sand/cement floor screed?

Also, does the screed simply go on top of the concrete or should the concrete be treated with anything first?

[Kalico]

Make sure the concrete floor is nice and wet before you start and use a VERY dry mix of about 5 sand, 1cement, with no lime etc. Hardly any water in it, AFAIK.

Rob

[PJ]

I was going to make the mix sloppy so it found it's own level. If I do a dry mix I'll have to float it smooth & level and having never done this before I may c*ck up.

[Stuart]

Depends on the thickness, if its about 10mm or less then a self levelling flooring compound that you pour on and it will create a thin hardwearing level surface. If your screed is needing to be a couple of inches thick then it does need to be a very dry mix (4:1 min) and levelled with a wooden float. If you make a wet and sloppy sand cement screed, it will be weak and dusty!

[PJ]

Right. See your point. I need a 65mm screed so it's quite thick. Self leveller is no good because it tends to flake off (this is a garage and so will take some stick).

[Mike Taylor]

"Normal screeds are above 50mm thickness up to about 75mm You lay them on top of the existing clean concrete.

1st "prime the concrete with a slurry of neat cement. Just mix some cement with water to a sloppy creamy consistency and brush with a broom onto the floor The screed is normally 3 parts river washed sand to 1 part cement mixed quite dry.

[PJ]

Please excuse my ignorance but what is river washed sand?

[Stuart]

It is widley known as "Sharp Sand", don't use Building Sand (often called Soft Sand) it will give a dusty finnish.

[Harry Bloomfield]

PJ has brought this to us :

From my memory of the last time I saw it done professionally, they laid a matrix of 2x2 level timber to act as a guide at a spacing of about 4 feet. As the screed starts to set, they lift the timber and fill in the gaps with more screed then float it smooth. They used sheets of ply on top of the screed to stand upon.

[David]

In article , PJ writes

It should be "washed river sand"

[Mike Taylor]

correct washed river sand instead of river washed sand, Slip of the old computer fingers when trying to type fast

[PJ]

Oh dear. And here's me with a ton of red building sand left over which I was going to use for the screed!