Todd Posted June 25, 2023 Share Posted June 25, 2023 Hi, First time post, so sorry if this is a daft question Currently building a single storey extension.Site is sloping downwards meaning with have a stepped footing . 2 steps , dug out to correct depth , overlap etc. As access is tricky, we will a line pump. We have shuttered sides and risers of steps. Question is ; when we pump concrete, what stops the concrete from finding its own level and effectively acting like a manometer , basically leveling out either side of shutter? Foundation are 8mx6.5 m with steps on the 6.5 m run Hope this makes sense Many thanks.. Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 25, 2023 Share Posted June 25, 2023 7 minutes ago, Todd said: Hi, First time post, so sorry if this is a daft question Currently building a single storey extension.Site is sloping downwards meaning with have a stepped footing . 2 steps , dug out to correct depth , overlap etc. As access is tricky, we will a line pump. We have shuttered sides and risers of steps. Question is ; when we pump concrete, what stops the concrete from finding its own level and effectively acting like a manometer , basically leveling out either side of shutter? Foundation are 8mx6.5 m with steps on the 6.5 m run Hope this makes sense Many thanks.. Does the above mean that you are independently planning, managing & supervising this pour? The lower slab needs to be cast first, and steels (starter bars) need to have been designed in by an SE to observe this type of execution. Others will be about to offer advice, but you defo need to start from the bottom, and work upwards! Link to comment Share on other sites More sharing options...
saveasteading Posted June 25, 2023 Share Posted June 25, 2023 You are right to think of this. Bodes well for the project. Concrete for a pump is an especially fluid mix of small aggregate, extra sand and a plasticiser to keep it moving. As such , it won't stand in a pile like normal concrete. Your shuttered stop-ends are the right thing to do. But the liquid in the mix will try to get through any gaps and the considerable force of standing concrete will try to knock the shutter over. So spike your shutters really hard with bars or timber battens....you can leave them in. You can spike into the trench sides as well as the bottom Perhaps add an extra shutter a few ft inside, as it will protect the main one. You could support it with some concrete in advance. Do not add any water to the mix, and be prepared to forbid it. Don't pour near to the shutter....let it flow from a safer position....the force can be huge. By anticipating problems you are ahead of the game. Have an imaginary pour when no-one is watching....where will you stand? How will you get an immediate message to the operator to turn off the pump? Lastly....brief your team about the risk we are discussing. Have good welllies and plenty of shovels. Safety wise...concrete burns skin. Ths stuff will splash. Have water handy. Wash well afterwards. Please report back! Good luck and enjoy it. Link to comment Share on other sites More sharing options...
saveasteading Posted June 25, 2023 Share Posted June 25, 2023 8 minutes ago, Nickfromwales said: Others will be about to offer advice, SE and contractor here. @Nickfromwalesis not wrong but it isn't complex science but anticipating problems. I am assuming the steps are 300mm or so, not huge ones. Link to comment Share on other sites More sharing options...
saveasteading Posted June 25, 2023 Share Posted June 25, 2023 1 Link to comment Share on other sites More sharing options...
Todd Posted June 25, 2023 Author Share Posted June 25, 2023 Hi, many thanks for the quick and clear replies.. To answer some questions. 1) myself and three other on site , 3 are family builders. I am householder and acting labourer 2) the builders have experience of pumped concrete and the pump guy they use is doing a site visit before pour. Not sure builders have done a stepped pour before. 3) footings are min 250, so we have two steps at 500 ( min ) 4) SE design and full plan approval for BC 5) building control have visited site We are using 18 mm ply with 90x40 mm bracing to hold sides.( Photos to big to upload).. I think it's a simple (?) job .,but my engineering background questions why the wet concrete doesn't find it's way under the step shutter and become a equal height throughout the trench.. Thanks again for your time and help.. 1 Link to comment Share on other sites More sharing options...
TonyT Posted June 25, 2023 Share Posted June 25, 2023 Make sure you have a concrete poker too to get rid of the entrapped air Link to comment Share on other sites More sharing options...
saveasteading Posted June 25, 2023 Share Posted June 25, 2023 One more thing. How are you controlling the levels? Probably your builders have a laser level. I always prefer to make it easy. Bang some pegs or rods into the base, and set the tops level. Or rods or long nails into the sides. Then simply concrete to the tops. One less thing to think about on the day. Link to comment Share on other sites More sharing options...
Conor Posted June 25, 2023 Share Posted June 25, 2023 2 minutes ago, Todd said: I think it's a simple (?) job .,but my engineering background questions why the wet concrete doesn't find it's way under the step shutter and become a equal height throughout the trench.. A couple concrete blocks thrown on top after you do the lower pour. What's the concrete volume? I'd reccomend using a team with wheelbarrows as you get away with a thicker mix. I helped a mate with his, 3.5m³, with three barrows in about 45mins. Good workout. Sounds like there's four of you on site so doable. 1 Link to comment Share on other sites More sharing options...
saveasteading Posted June 25, 2023 Share Posted June 25, 2023 Agreed barrows and for the same reasons, as long as you can get them there. This reduces the risks and mess too. At the end of pumping you have to wash the hopper and tubes out.....very messy. I'm all for hi-tech but it seems ott here. Even pokers aren't needed if you can agitate thoroughly with shovels. Link to comment Share on other sites More sharing options...
Todd Posted June 25, 2023 Author Share Posted June 25, 2023 Hi, thanks again for your help. 1) to get height, builder will use laser to get line, then spray paint line all way round on inside of shutter. 2) access lane to house is tight..too narrow for mixer , everything is offloaded about 100 yrds away. There is no way to get mixer on drive.. so options of dumper, but hard to pour due to slope or pump. 3) total volume for day is approx 14m3 , stepped part of foundation accounts for 6m3. Connor, Idea of putting weight on lower part is to counteract upward pressure of concrete trying to raise up ? Thanks... Link to comment Share on other sites More sharing options...
saveasteading Posted June 25, 2023 Share Posted June 25, 2023 51 minutes ago, Todd said: 3) total volume for day is approx 14m3 29m run incl double counting the corners. X 0.6 x 0.25 With no calculator or paper to hand, that is about 4.5m3 round up to 5m3. Link to comment Share on other sites More sharing options...
Todd Posted June 25, 2023 Author Share Posted June 25, 2023 Sorry if my previous post was misleading.. There are approximately 6m3 in the extension foundation, This foundation has the stepped element, however on the same day we are also pouring porch ,garage and some retaining wall .that volume is about 8m3 in total.. So on the day we shift 14 M3 in total . I still don't understand if the stepped element of the pour would self level, giving same height either side tho.. Link to comment Share on other sites More sharing options...
Conor Posted June 25, 2023 Share Posted June 25, 2023 2 hours ago, Todd said: Connor, Idea of putting weight on lower part is to counteract upward pressure of concrete trying to raise up ? Thanks... The blocks simply act as a dam. A medium density block is a little bouyant in a wet concrete mix, they will partially sit on top of the lower pour, and stop concrete on top from flowing down. At this time of year, the concrete will start going off pretty quickly, even a pump mix. Btw, with that access and volume, pump is the way to go. Link to comment Share on other sites More sharing options...
saveasteading Posted June 25, 2023 Share Posted June 25, 2023 1 hour ago, Todd said: still don't understand if the stepped element of the pour would self level, giving same height either side tho No it wouldn't. . The concrete is not self levelling and you have to control the level by manoeuvring the hose, then using shovels and rakes. It is sloppy and will seep through gaps but not pour through and rise on the other side. And it doesn't self level. Link to comment Share on other sites More sharing options...
Todd Posted June 25, 2023 Author Share Posted June 25, 2023 Thank you all for for taking time to reply.. It's reassuring to hear the voices of experience. Happy to hear that it's more about pushing it into position, rather than it flowing and finding its own level.. Iv poured straight from the mixer into a strip footing before , but this is first time for pumps and steps..going to have those blocks to hand tho! Will be back when pour is done, just to let you know how it went.. Many thanks, and sorry if it was a daft question... 1 Link to comment Share on other sites More sharing options...
saveasteading Posted June 25, 2023 Share Posted June 25, 2023 It would have been daft after the event. Good luck. Link to comment Share on other sites More sharing options...
Canski Posted June 25, 2023 Share Posted June 25, 2023 If I have steps I pour some concrete to the lower level bit against the shutter first then let it start to go off as you pour the rest. Depends how long you are going to take I suppose. Link to comment Share on other sites More sharing options...
Dave Jones Posted June 26, 2023 Share Posted June 26, 2023 pump it behind the shutter (use scaffold planks cut and spiked in with 10mm rebar), make sure its not too wet. let it fill then move to other end of the pour. it will be fine. I hammered in lengths of batten into the footing every 1.5m then lasered the tops, an easy way to know if your level as you work your way round. Link to comment Share on other sites More sharing options...
Todd Posted July 11, 2023 Author Share Posted July 11, 2023 Just an update Concrete pour was yesterday, pumped just over 21 m Pump line was 125 yrds.. Stepped footing was fine, started from lower part , then went to top. Shuttering is coming off today Thank you for all your advice, that's the first major hurdle out of the way.. 2 Link to comment Share on other sites More sharing options...
saveasteading Posted July 11, 2023 Share Posted July 11, 2023 Well done. Anything you would do differently next time? Link to comment Share on other sites More sharing options...
Todd Posted July 11, 2023 Author Share Posted July 11, 2023 Thanks, Probably next time is not to over think things.. We did use a company that dry mix the concrete, rather than it arrive wet, also waited until all 3 concrete lorries arrived before pumping Understand having a continuous flow , help prevent blocking. Surprised how stiff mix was, somehow being pumped and had expected it a lot more fluid. So 4 guys plus pump guy, did the pour in 3 hrs.plus set up and wash out at the end..which took longer than the pour Was surprised pump lorry could be controlled remotely from so far away..guy had handset to stop , start pump as we moved around. 1 Link to comment Share on other sites More sharing options...
TonyT Posted July 11, 2023 Share Posted July 11, 2023 Glad it went well a good milestone Link to comment Share on other sites More sharing options...
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