bradders3109 Posted March 27, 2021 Share Posted March 27, 2021 Hi all, I have today attempted my first concrete slab. It isn't a big room about 2.75m by 3.5m . We are replacing a suspended timber floor so the walls are already built which made things difficult. It was a day full of choice language and despite the best efforts of myself and the ministry of fun we have made a bit of a mess. The result is a slab that rises and falls by up to about 15mm in places. I am thinking that I could go over it with a thin screed or self levelling compound but don't know if this is a good or bad idea. the slab will be covered with 150mm of celotex and a final screed so won't be seen but i'll always know that it isn't level. Is there a product that I can use on a newly laid slab to level it and cover imperfections. Your help and suggestions will be greatly appreciated. Link to comment Share on other sites More sharing options...
JamesP Posted March 27, 2021 Share Posted March 27, 2021 (edited) From my limited experience I would say don't panic. With Celotex on top, the final screed will determine the level for your final floor covering. What thickness is the final screed? Edited March 27, 2021 by JamesP Link to comment Share on other sites More sharing options...
nod Posted March 27, 2021 Share Posted March 27, 2021 If you intend to cover it with 70 mil s&c screed Leave it as it is and you can easily sort it out with the screed Link to comment Share on other sites More sharing options...
bradders3109 Posted March 27, 2021 Author Share Posted March 27, 2021 Hi James there will be UFH on the celotex and then 65mm screed. Link to comment Share on other sites More sharing options...
bradders3109 Posted March 27, 2021 Author Share Posted March 27, 2021 1 minute ago, nod said: If you intend to cover it with 70 mil s&c screed Leave it as it is and you can easily sort it out with the screed does it not need to be level for the celotex? Link to comment Share on other sites More sharing options...
JamesP Posted March 27, 2021 Share Posted March 27, 2021 Just now, bradders3109 said: Hi James there will be UFH on the celotex and then 65mm screed. It will be fine. Now go have a drink and relax. Link to comment Share on other sites More sharing options...
Onoff Posted March 27, 2021 Share Posted March 27, 2021 It'll be fine. If really worried put a thin bed of sharp sand down and level that. Where is your dpm going or is that already in? Link to comment Share on other sites More sharing options...
bradders3109 Posted March 27, 2021 Author Share Posted March 27, 2021 Already on my fourth bottle ☹️ 1 Link to comment Share on other sites More sharing options...
bradders3109 Posted March 27, 2021 Author Share Posted March 27, 2021 2 minutes ago, JamesP said: It will be fine. Now go have a drink and relax. Just now, Onoff said: It'll be fine. If really worried put a thin bed of sharp sand down and level that. Where is your dpm going or is that already in? DPM is under the slab but laps up the walls by another 400mm to take it above the celotex and screed. Link to comment Share on other sites More sharing options...
bradders3109 Posted March 27, 2021 Author Share Posted March 27, 2021 4 minutes ago, Onoff said: It'll be fine. If really worried put a thin bed of sharp sand down and level that. Would you just leave the sharp sand loose or mix it with cement and SBR to form a screed? Link to comment Share on other sites More sharing options...
PeterW Posted March 27, 2021 Share Posted March 27, 2021 2 minutes ago, bradders3109 said: Would you just leave the sharp sand loose or mix it with cement and SBR to form a screed? Sharp sand, laid dry and levelled into the hollows. Then Celotex, slip membrane and screed. 1 Link to comment Share on other sites More sharing options...
nod Posted March 27, 2021 Share Posted March 27, 2021 6 minutes ago, bradders3109 said: does it not need to be level for the celotex? No it doesn’t The celotex sheets often cause bumps and humps As long as your screed doesn’t drop below 50 mil on the high spots You will be ok Link to comment Share on other sites More sharing options...
bradders3109 Posted March 27, 2021 Author Share Posted March 27, 2021 I thank you all very much and am feeling a little better already. I won't try self mixing a slab again though. sharp sand under the celotex it is then. Link to comment Share on other sites More sharing options...
Onoff Posted March 27, 2021 Share Posted March 27, 2021 I'd leave it loose. Not much difference to what I did blinding my hardcore. Looks great when it's done! You doing any more rooms? I screwed screed rails to the stud walls and used a drag board to get the concrete dead level. No screed, I just tiled on top. Pity my tiling's crap! Link to comment Share on other sites More sharing options...
Onoff Posted March 27, 2021 Share Posted March 27, 2021 14 minutes ago, bradders3109 said: Already on my fourth bottle ☹️ Red or white? 1 Link to comment Share on other sites More sharing options...
bradders3109 Posted March 27, 2021 Author Share Posted March 27, 2021 2 minutes ago, Onoff said: Red or white? lager mate. can't face the claret tonight. 1 Link to comment Share on other sites More sharing options...
bradders3109 Posted March 27, 2021 Author Share Posted March 27, 2021 5 minutes ago, Onoff said: You doing any more rooms? I screwed screed rails to the stud walls I did screw rails to opposing walls but with trying to mix, barrow into the room and tamp level it got in front of me. The missus was filling buckets ready for the next mix. Link to comment Share on other sites More sharing options...
Onoff Posted March 27, 2021 Share Posted March 27, 2021 3 minutes ago, bradders3109 said: I did screw rails to opposing walls but with trying to mix, barrow into the room and tamp level it got in front of me. The missus was filling buckets ready for the next mix. You'll be more aware / better prepared next time! 1 Link to comment Share on other sites More sharing options...
Roundtuit Posted March 27, 2021 Share Posted March 27, 2021 Don't beat yourself up! That's probably better than happens on many sites (particularly on a Friday afternoon). Improvise, adapt and overcome ? 1 Link to comment Share on other sites More sharing options...
bradders3109 Posted March 28, 2021 Author Share Posted March 28, 2021 Thanks for the replies gents. The reassurance and encouragement makes a massive difference to a Virgin self builder. I’ve looked at it again this morning and it’s worse than I originally thought. However 20mm of sharp sand will level it up and cover the eyesore. The positive is that the slab is drying solid although the depth will be variable between 100 and 120mm. Thanks again. Link to comment Share on other sites More sharing options...
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