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[Sir Tigger KC]

I've got a good base of concrete down and just have to lay the screed on top, which I was planning on doing tomorrow.  Trouble is while sweeping it today I noticed that the concrete still seems a bit damp...

Should I wait a few more days for it to dry out properly or will it be OK to lay the screed as is? 

I've never done this before and it's a bit of a learning curve!!  Thanks!! 

[RobG]

You should allow one week per cm thickness of concrete, up to 4 cm. Allow twice as much time for the remaining thickness more than 4 cm. In other words, for a thickness of 6 cm, you must allow minimum (4 x 1) + (2 x 2) = 8 weeks drying time. For concrete thicker than 6 cm, allow 4 weeks drying time per additional cm.
Don`t forget a membrane must be laid between the sub-floor concrete and the screed.

[ozzycat]

you dont have to lay a membrane between the base and the sceed the screed is only a self leveling top coat
the building co iwas plant eng never laid one under the screed but did between the substrait  &base coat of concrete

[cem_devecioglu]

You should allow one week per cm thickness of concrete, up to 4 cm. Allow twice as much time for the remaining thickness more than 4 cm. In other words, for a thickness of 6 cm, you must allow minimum (4 x 1) + (2 x 2) = 8 weeks drying time. For concrete thicker than 6 cm, allow 4 weeks drying time per additional cm.
Don`t forget a membrane must be laid between the sub-floor concrete and the screed.

Robg , is there any code or standard for that mix ? (I guess probably this is the standard mix which is sold publicly in UK)

[RobG]

Screed mix is generally 3 parts sharp sand to 1 part cement but you can go to 4:1 or at a push 5:1

[cem_devecioglu]

Screed mix is generally 3 parts sharp sand to 1 part cement but you can go to 4:1 or at a push 5:1

in oil wells there were some special mixtures that dry quickly but very expensive.. nowadays there are also some "quick" mixes around but I cant  trust them

[cem_devecioglu]

here are some types
http://iti.northwestern.edu/cement/monograph/Monograph3_8.html

[markrnorton]

You should allow one week per cm thickness of concrete, up to 4 cm. Allow twice as much time for the remaining thickness more than 4 cm. In other words, for a thickness of 6 cm, you must allow minimum (4 x 1) + (2 x 2) = 8 weeks drying time. For concrete thicker than 6 cm, allow 4 weeks drying time per additional cm.
Don`t forget a membrane must be laid between the sub-floor concrete and the screed.

Is this drying time or time to reach full structural integrity ?

[paul.lovejoy]

membrane DPM is normally under concrete slab but if i am say converting a gargage on an existing slab i do put one between the new screed as well as insullation 

whats the concrete floor for Tigger not that i will tell you when to lay the screed i am just nosey

we normally wait at least 4 weeks but then there are always other things to do RobG calcs probably spot on

plus coat the slab in unibon/pva the white gooey sticky stuff before you lay the screed

screed mix is a bit of an open bag  normally i use 4 : 1 although others say 3 or 5 :1

we are just laying a screed now and got a ready mix company in only a cubic metre @ £175 but time you pay for materials and labour to knock it up etc bloody good price me thinks plus they can put a retarder in it to delay it going hard if you want

[paul.lovejoy]

oh yes and if it is a big area dont get the ready mix with the drum get the big lorry that mixes on site you only pay for what you use

[ozzycat]

oh yes and if it is a big area dont get the ready mix with the drum get the big lorry that mixes on site you only pay for what you use

+ 1

[Gaffers]

If I have learnt anything out here it is that if you are intending on putting anything heavy on the concrete wait at least 28 days.  You may have problems otherwise

[paul.lovejoy]

If I have learnt anything out here it is that if you are intending on putting anything heavy on the concrete wait at least 28 days.  You may have problems otherwise

did not think you were that fat heavy well built mind you you l;ook good in shorts you beast

[Gaffers]

If I have learnt anything out here it is that if you are intending on putting anything heavy on the concrete wait at least 28 days.  You may have problems otherwise

did not think you were that fat heavy well built mind you you l;ook good in shorts you beast

I'm 3 stone lighter than you last saw me, tubs 

It was an MRI scanner built in to a truck trailer.  Awesome bit of kit 

[Sir Tigger KC]

Thanks for all the replies!! 

It's a lounge floor, so nothing too heavy will go on it....    Well... 

I've got the DPM underneath the concrete slab.  Why do you coat the slab with PVA Paul? does it provide another layer of damp proofing? 

I'm going to put laminate on it when it's done, so I guess another few weeks drying before I do that? 

Thanks again!!