Floor prep

[plasterman2]

Hi Ive been asked to screed a small floor in an extension i plastered but not sure what prep i need to do on the concrete first if any ?

 

[KevRM]

if its straight onto concrete base just cement slurry it

 

[plasterman2]

ok thanks should i lightly hose floor first and just cement and water slurry or sbr

 

[gooner59]

Alway's put Sbr in if you can mate !, plus neat opc whisk until a slurry as you said kill the suction on the concrete with a splash of water then slurry and lay screed into it while it is still wet !! and bobs your uncle !!

 

[essexandy]

Unusual for no insulation to be going down but if that's the case just wet the floor and then using a broom sweep a bit of your screed gear around as a slurry. No need for for SBR.

 

[malc]

essexandy is correct. do not put a cement grout or on the oversite. this idea finished years ago as the cement slurry dried quicker then the screed causing the screed to become hollow. either sweep screed on to the oversite, or just wet it. i would use sbr if the screed was about 1 inch thick.

 

[cashandben]

I always cement slurry concrete floors, never had a problem, always best to add SBR to it but killing the suction in the key, i always get the floor soaked the night before if possible. Geoff

 

[essexandy]

Screeding is know different to rendering, you don't have to kill the suction just lessen/control it.

 

[malc]

I always cement slurry concrete floors, never had a problem, always best to add SBR to it but killing the suction in the key, i always get the floor soaked the night before if possible. Geoff

i am very surprised that you are still cement grouting the oversite. we where told to stop doing this about 30 years ago when i was subbing off oconnells who was the largest floor screeding company in the country at the time. the reason as i have said was the grout dried out quicker then the screed causing it to go hollow.

 

[cashandben]

Screeding is nothing like rendering, with rendering you need a bit of suction otherwise you'll be hanging around all day, and its not really bonded to the scratch coat, with a floor screed you need to kill the suction and bond to the concrete with grout, sbr etc the last thing you want is it sucking the moisture out of the screed as it causes shrinkage cracks.

 

[malc]

cashandben i agree i do not want suction when i am screeding, although it is not very often that i have to lay straight on the oversite now.

 

[essexandy]

Screeding is nothing like rendering, with rendering you need a bit of suction otherwise you'll be hanging around all day, and its not really bonded to the scratch coat, with a floor screed you need to kill the suction and bond to the concrete with grout, sbr etc the last thing you want is it sucking the moisture out of the screed as it causes shrinkage cracks.

Mate I've done many hundreds of screeds so I do know what's what with them. Although I wouldn't want loads of suction from an oversite or block and beam floor either I certainly don't go to unnecessary lengths to completely kill it either. A little suction can actually help with bonding a screed just as it does with rendering.
Not sure if I read that right but I definitely consider my top coat rendering to be bonded to the scratch coat.