RichS Posted March 3, 2018 Share Posted March 3, 2018 Has anyone had any issues when pump pouring a passive slab?? The reason I ask is because I have, and it was a major pain in the arse. Two weeks ago we had a very short spell of warmer weather and so I booked in my slab pour with my chosen contractor. To cut a long story short it all went tits up. They pumped in a self compacting concrete, which they thought would be ok, and all it did was float the top layers of insulation along with the steel on top. Luckily we managed to salvage the steel but approx 3 - 4 cube had to be jack hammered out the next day. The company in question were great about it, held up their hands straight away and we came to suitable arrangements, I have no gripe with them whatsoever. My issue now is I need to prepare for the next warm spell so that I can try again. It will not be with the same company as they do not lay anything other than self compacting, which clearly is not suitable. So what I need to ask is what grade have others used, with a pump, and had no issues. I assume a standard C25/30 mix that doesn't flow like self compacting, i.e. requires vibrating, is the solution but is this classed as pumpable??. Link to comment Share on other sites More sharing options...
IanR Posted March 3, 2018 Share Posted March 3, 2018 (edited) It's possible they poured directly in to the ring beam before weighting down the top layers of EPS. They need to let it gently flow into the beams after first pouring on to the EPS in the 100mm thick areas. What did the Engineer specify, most are C35 Edited March 3, 2018 by IanR Link to comment Share on other sites More sharing options...
Onoff Posted March 3, 2018 Share Posted March 3, 2018 From what others have said on here would it pay to have a power float available? There's been some horror stories on here of late with finished slabs being anything but flat and level. Link to comment Share on other sites More sharing options...
Gone West Posted March 3, 2018 Share Posted March 3, 2018 (edited) I also had problems with my passive slab, details in my blog, although not the same as yours. The slab is 200mm thick all over and the second attempt, which I had pumped with C35, was fine. On ours the DPM was on top of the polystyrene and held down by the steel and the concrete was pokered. When I had mine done self compacting/levelling wasn't really an option but I would have used it had it been available. Edited March 3, 2018 by PeterStarck Link to comment Share on other sites More sharing options...
RichS Posted March 3, 2018 Author Share Posted March 3, 2018 (edited) @PeterStarck, Yes, if the DPM had been laid on top of the polystyrene it would not have been a problem and the slab would all have been laid and finished in about 4 hours. I have set out the slab as per SE drawings, and indeed as can be seen here, https://www.youtube.com/watch?v=uEiRXB81WJM I believe that others have laid their slabs out the same, with insulation on top of the DPM, and wondered if they had encountered any problems. Fortunately I started the pour in the attached garage area and so didn't have any heating pipes to contend with when I had to hastily start removing the steel but it certainly is not an experience that I want to go through again the next time I try to pour. For what it's worth, as I have had to remove all the steel, insulation and damaged DPM from the garage area I was considering laying a second, thinner layer of DPM over the top of the insulation, under the steel, for the next attempt. Obviously I can't do this for the main floor area without removing all the heating pipes, steel etc and then re-instating it. Edited March 3, 2018 by RichS Link to comment Share on other sites More sharing options...
Alexphd1 Posted March 3, 2018 Share Posted March 3, 2018 we used c35 pump mix approx 70mm sump 10mm aggreagate (i will double check aggreagate if you want) . certainly not self leveling, lot of work involved to spread out. Our dpm was on the 1st 100mm eps and up to 200mm eps above this, no problems. Link to comment Share on other sites More sharing options...
Russell griffiths Posted March 3, 2018 Share Posted March 3, 2018 What @IanR said makes a lot of sense, did the flow able concrete get under the insulation and actually lift it rather than the insulation actually floating. Highlighting what went wrong could help others avoid this horrible experience. Link to comment Share on other sites More sharing options...
Alexphd1 Posted March 3, 2018 Share Posted March 3, 2018 I am not 100% sure on self levelling concrete, is it a similar consistency to liquid screed stuff? Link to comment Share on other sites More sharing options...
RichS Posted March 4, 2018 Author Share Posted March 4, 2018 @Alexphd1, Thanks for that offer, yes I would appreciate it if you could check the aggregate size and let me know. It may need to be 10mm with such a low slump to allow it to be pumpable. Yes, SC concrete is very liquid, lots of plasticiser in the mix so although it contains aggregate it is very much like a thick screed in its consistency. @Russell griffiths, not sure on the difference between the flow getting under and lifting versus floating, that's a bit of a chicken or egg question. The end result was the same however so I would certainly not recommend SC concrete for a passive slab unless you cover all the insulation with the DPM which is what I would do in future, regardless of SE drawings. Link to comment Share on other sites More sharing options...
Onoff Posted March 4, 2018 Share Posted March 4, 2018 (edited) Ive been using de-aerator additive for a good while now in the few small slabs I've done (sheds, bathroom,sliding gate base). The "mix" just doesn't "bubble" as in as you tamp it down air doesn't appear to come up. I have only used the Everbuild Liquid Waterproofer (T'station do it) and only noted the de-aeration properties in the small print after buying the first lot for waterproofing purposes. Cheap as and seems to work. Surely negating air must assist with the self compacting properties? Do the big commercial size mixes say for passive slabs add anything like this? Edited March 4, 2018 by Onoff Link to comment Share on other sites More sharing options...
RichS Posted March 4, 2018 Author Share Posted March 4, 2018 @PeterStarck Just read your blog Peter. That was really bad luck with your slab pour. I think if i had reached that stage I would be tempted to call it a day. Did you have to stand the cost of all the new materials etc?? Link to comment Share on other sites More sharing options...
willbish Posted March 4, 2018 Share Posted March 4, 2018 Ditto, have just read your blog @PeterStarck. Have you talked about this incident elsewhere on the forum, apologies if you have Was it immediately obvious after the pour that there were voids? Was the concrete vibrated? What other costs were cut, other than lack of pump to cause this? I suspect insufficient labour may have been a factor Link to comment Share on other sites More sharing options...
Triassic Posted March 4, 2018 Share Posted March 4, 2018 (edited) I’m due to start my insulated foundations on a couple of weeks, so any learning greatfully received . looking at my drawings the architect has the radon barrier between the insulation layers to protect it from puncture during steel placement. I’m thinking that I need to contain any liquid in the concre as the liquid is likely the cause of the floating insulation. I’m thinking I’ll use cheap plastic sheeting over all the insulation to stop any liquid migration. A few punctures shouldn’t be a problem. Edited March 4, 2018 by Triassic Link to comment Share on other sites More sharing options...
RichS Posted March 4, 2018 Author Share Posted March 4, 2018 28 minutes ago, Triassic said: I’m thinking I’ll use cheap plastic sheeting over all the insulation to stop any liquid migration. A few punctures shouldn’t be a problem. This is exactly what I am going to do when I re-instate the garage area later this week. Unfortunately the main house area is already laid out complete with heating pipes attached to the mesh so I will have to run with it and hope the less fluid standard mix does not cause the same problems. Watching the YouTube clip I attached earlier and also @Alexphd1 experience would all point in the right direction. Link to comment Share on other sites More sharing options...
Triassic Posted March 4, 2018 Share Posted March 4, 2018 Low expansion foam all the joints Link to comment Share on other sites More sharing options...
RichS Posted March 4, 2018 Author Share Posted March 4, 2018 3 minutes ago, Triassic said: Low expansion foam all the joints That had been done, so they all floated nicely together 1 Link to comment Share on other sites More sharing options...
Triassic Posted March 4, 2018 Share Posted March 4, 2018 So was the self leveling concrete the problem, too much liquid. Maybe use thicker mix next time. Link to comment Share on other sites More sharing options...
IanR Posted March 4, 2018 Share Posted March 4, 2018 (edited) Here's mine during the pour. The DPM is over the bottom layer of EPS and up over the EPS upstand. If you pour directly into the ring beam then there is a risk of the liquid getting under the uncovered EPS and it floating "away", hence pouring on to the higher areas to weight it down and letting it gently flow into the ring beams. This is not an issue with self-compacting, it can happen with C35. Edited March 4, 2018 by IanR 2 Link to comment Share on other sites More sharing options...
Dudda Posted March 4, 2018 Share Posted March 4, 2018 I always specify a separating layer on top of insulation. If you put the Radon below or between the it doesn't matter. Usually below if coordinating trades is easier and between protects is better. Don't have the radon above the insulation as it will get punctured when placing the steel or UFH pipes. A separating layer on top of the insulation can be a 1000 gauge polythene and is very quick and cheap. If it gets one or two holes it's not a big issue. This stops any concrete seeping between cracks in the insulation (which you shouldn't have to start with) thus creating a thermal bridge. It's also useful if you've pipes or other services cut into the insulation layer as it stops any concrete seeping down around these. Link to comment Share on other sites More sharing options...
RichS Posted March 4, 2018 Author Share Posted March 4, 2018 18 minutes ago, IanR said: This is not an issue with self-compacting, it can happen with C35. I wouldn't dispute that it can happen with a standard mix, but with a low slump the chances are greatly reduced as the concrete doesn't flow. And yes, loading onto the top and letting it flow into the ring beam has got to be a good help. Link to comment Share on other sites More sharing options...
RichS Posted March 4, 2018 Author Share Posted March 4, 2018 @IanR How many cubic metres did that lot take?? Quite a few I'd guess. Link to comment Share on other sites More sharing options...
IanR Posted March 4, 2018 Share Posted March 4, 2018 It was almost 8 loads, so around 60m3 Quick service though, concrete was in by 11:30, just took the rest of the day to level and power-float. Link to comment Share on other sites More sharing options...
RichS Posted March 4, 2018 Author Share Posted March 4, 2018 8 minutes ago, IanR said: It was almost 8 loads, so around 60m3 Quick service though, concrete was in by 11:30, just took the rest of the day to level and power-float. Impressive!! I'm assuming the concrete was pumped in with a ground line pump?? Link to comment Share on other sites More sharing options...
Gone West Posted March 4, 2018 Share Posted March 4, 2018 @RichS and @willbish The cost of the removal and the replacement works were borne completely by the company laying the slab. As I had video evidence of the work being done and the time taken they accepted liability and in that respect can't be faulted. There was some half hearted vibration work done but the concrete was going off before it could be laid properly. The cost cutting included not pumping and using a concrete supplier whose depot was too far away. The weather being quite warm didn't help matters. After ultra-sonic testing showed cavities, core samples were taken to verify the fact. After that there was nothing to do other than complete removal. 1 Link to comment Share on other sites More sharing options...
IanR Posted March 4, 2018 Share Posted March 4, 2018 47 minutes ago, RichS said: I'm assuming the concrete was pumped in with a ground line pump?? Boom pump, had heck of a reach on it: 1 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now