floor screeding

[marlb]

Hi all,
I have had a bit of advice from someone I do not know that well so I thought I would run it passed some experts..

I am about to screed a floor to a depth of 20-25mm. I know this is not deep enough for a standard screed mix so I have been asking around for some advice. I do not want the screed to crack.

Is it ok to mix Grano dust into the screed mix? He said to substitute half of the grit sand for Grano dust and mix 4:1 with cement. Have tryed to get hold of granite chippings with no luck..

Or is grano dust and granite chippings the same thing??

any help appreciated

 

[The-brickie]

I use fibres in thin screeds, most BMs stock them and I've seen them in B&Qs, dont know about that grano stuff......

 

[noseall]

granno' chippings, sets like bell metal.

 

[The-brickie]

Is it a northern thing, not seen it down here?

 

[marlb]

Thanks guys,

Noseall,

You mentioned grano chippings. I have bought Grano dust is it one and the same thing? The reason I ask is that the dust I have bought is more like a black sand. It does not seem to have any chippings as such.

 

[noseall]

the dust is used for finishing a surface the chippings are mixed within.

 

[marlb]

Oh dear! Best I take the dust back.

Any idea where I can get hold of the chippings????
Keyline sold me the dust but they don't do chippings

 

[noseall]

keep the dust and mix the two together, best of both worlds.

 

[noseall]

the problem with any screed is 'lift'

a thicker screed will have weight. therefore a thinner screed will be more vulnerable to separation.

increase the cohesive capacity by thoroughly wetting the substrate first. the granite mix will help contain the rigidity of the screed whether it lifts or not.

 

[Shytalkz]

Stick some chicken mesh in to control cracking, mid-depth. 25 thick is pushing it, though...

 

[marlb]

Thanks again Nose all, I will keep the dust and use both as suggested.
Sorry to be a pain!!

Any idea where I can get hold of the chippings. I have searched on Google but can only get bulk bags (1 tonne or 1/2 tonne). I only need enough for 0.14m3 (6 bags).

 

[marlb]

Shytalk,

I don't know of any other way to get the level of the floor, upto the same level of the room I have knocked through too.

That was a mouthful!!!

I will be tiling over afterwards with 12mm natural stone..

 

[noseall]

the fact that you are tiling will help a great deal. an interlocking cement based floor covering will help with rigidity and make the whole floor more steadfast.

 

[Shytalkz]

Could try this as an alternative with more chance of success: http://www.ardex.co.uk/pdfs/ardex s21.pdf. Expensive though, from memory

 

[marlb]

Thanks guys great advice.

Anyone know where to get the granite chippings?