Vijay Posted February 4, 2017 Share Posted February 4, 2017 I'll have over 400 L rebars to go into the concrete footings. They're 800x200 and have to sit 400 into the concrete and 400 out. I wondered how long I have to wait after the concrete pour is finished before I put them in the concrete? Cheers Vijay Link to comment Share on other sites More sharing options...
RichS Posted February 4, 2017 Share Posted February 4, 2017 Hi Vijay, Any reinforcing bars should be tied into the footings before any concrete is poured. If you were to try pushing them in afterwards they would simply displace the concrete and not be held securely. Link to comment Share on other sites More sharing options...
Vijay Posted February 4, 2017 Author Share Posted February 4, 2017 Hi Rich, Not sure what you mean by tied in? The footings are trench footings of 600 and 900 deep Link to comment Share on other sites More sharing options...
RichS Posted February 4, 2017 Share Posted February 4, 2017 Ah, right, I see. In that case if you have to insert them into the footings after pouring you would need to do it whilst the concrete is still fairly wet in order to be able to consolidate the bars into the foundations, but not when it's so wet that the bars fall over/sink. The only other alternative that I can think of is suspend the bars to the required depth, but that would be a pain in the arse job. Link to comment Share on other sites More sharing options...
Vijay Posted February 4, 2017 Author Share Posted February 4, 2017 That's exactly what I thought but wondered how long after the concrete is poured would it have set enough to support the L bars? I've attached a drawing of one of the foundation details Link to comment Share on other sites More sharing options...
Triassic Posted February 4, 2017 Share Posted February 4, 2017 (edited) Maybe you need to use a price of timber with a hole, slightly smaller than the rebar, drilled into them, hammer the rebar into each peice of wood to the required depth, then nail each piece of timber in the correct place across the trench formers. Do this before pouring the concrete. Edited February 4, 2017 by Triassic Link to comment Share on other sites More sharing options...
MikeSharp01 Posted February 4, 2017 Share Posted February 4, 2017 You need to make a frame to hold the L bars in place ready for the pour and pour around them. You should not insert them after the pour because: a. You won't be able to get them placed accurately - if you push them into very loose concrete they will probably move either sink or fall over. B. 400 will take time and even if you get the first into the concrete by the last it will have gone off. C. You need to vibrate / poker the concrete to ensure it flows around the bars which are profiled to ensure they are held firm and you cannot vibrate concrete that has started to harden. Sadly a frame is required. Link to comment Share on other sites More sharing options...
Russell griffiths Posted February 4, 2017 Share Posted February 4, 2017 It's fairly easy really, done it loads. If you have a set of profile boards at either end of the footing mark a line on here where the reo has to go in. Between these marks pull something taught. Either a brickies line or fencing wire, you can now push your reo in giving it a good wiggle up and down to get a good secure hold, if you put a paint mark on the Reo you will know how far to insert it. You can tie it back to the line or just sort of balance it against the line while the concrete sets. What at I think a lot of people are guilty of is overthinking things, you are not building the space shuttle this stuff is used by groundworers on a building site in the mud and rain, as long as you are accurate to about 50 mm you will be spot on. Remember when that concrete has set it is very easy to bend them all nice and straight so they line up with the next stage. CAUTION. Buy some plastic caps to go on top of the exposed reo. A poke in the eye or falling on one could be nasty. 1 Link to comment Share on other sites More sharing options...
Barney12 Posted February 5, 2017 Share Posted February 5, 2017 As above the only one occasion I've done something like this (and it was only a few meters) the ground worker pulled a tight line, marked the rebar and pushed them in. Zip tie the rebar to the line to hold it in position. Link to comment Share on other sites More sharing options...
Onoff Posted February 5, 2017 Share Posted February 5, 2017 I would not, no way, no how, never, push the bars in afterwards. As above, piece of timber to suspend them and then pour, vibrate. Sticking in afterwards also risks allowing water to run down the gap around the bar. I've been putting cranes/cleaning rigs running in rails on roofs for the last 34 years and the holding down units are always suspended in timber boxes etc then the concrete added. Bus man's holiday but did similar on my brother's astronomy pier: Link to comment Share on other sites More sharing options...
Russell griffiths Posted February 5, 2017 Share Posted February 5, 2017 47 minutes ago, Onoff said: I would not, no way, no how, never, push the bars in afterwards. As above, piece of timber to suspend them and then pour, vibrate. Sticking in afterwards also risks allowing water to run down the gap around the bar. I've been putting cranes/cleaning rigs running in rails on roofs for the last 34 years and the holding down units are always suspended in timber boxes etc then the concrete added. Bus man's holiday but did similar on my brother's astronomy pier: I think the problem here is two different jobs are getting confused. You have put up a picture of a base plate being used to hold up a column you hav made a ply former to hold the base in position and it looks spot on??. What the lad wanted to know was a starter bar a length of reo 800 long with a 90 degree bend and a 200 return if you think you are going to pull that out once it is set then I don't know what you think you are building. If you give it a good wiggle the slurry will run around the reo to seal it off. If you are concerned about water ingress then it shouldn't be cast in two pieces like it is going to be as there will always be a cold joint. Also i like you accurate way you said you would do it but it is not needed or warranted. The last footing I did had a linear run of 123m if you were putting a starter bar in at 600mm centres that would be approx 200 bars if you think you are going to mark that out on a bit of timber and fix it in place to hold them up with holes drilled in it, I will leave you to it, I'll go fishing and come back and pick you up tomorrow, As I said I think different jobs are getting mixed up here it's a starter bar in a footing not the space shuttle. Link to comment Share on other sites More sharing options...
Vijay Posted February 5, 2017 Author Share Posted February 5, 2017 Cheers for the replies. I think timber supports would be a mammoth task as I have at least 437 L bars over 131 linear metres (300 spacing). Even using string would need a trial beforehand I reckon as some of the spans are quite long and I'd imagine the string/cable would need supporting. What would the max span the support string/cable could be stretched too, holding L bars every 300mm without dipping? Link to comment Share on other sites More sharing options...
Declan52 Posted February 5, 2017 Share Posted February 5, 2017 How are you putting the concrete into the trenchs , digger bucket, wheel barrow or pump?? Unless the steel is tied together if you tip a load of concrete into the trench it will tip the L bars over. Could you buy some lengths of 5mm bar and put a strip at the bottom and top so you end up with maybe a 2m long bit of steel cage that will be much quicker to drop in during the pour. The top length of 10mm can be reused if needs be. This is how I seen it being done on a ring beam. 1 Link to comment Share on other sites More sharing options...
iSelfBuild Posted February 5, 2017 Share Posted February 5, 2017 (edited) 1 hour ago, Vijay said: Cheers for the replies. I think timber supports would be a mammoth task as I have at least 437 L bars over 131 linear metres (300 spacing). Even using string would need a trial beforehand I reckon as some of the spans are quite long and I'd imagine the string/cable would need supporting. What would the max span the support string/cable could be stretched too, holding L bars every 300mm without dipping? Timber batons would be the best bet IMO... Stack a few 4.8m batons on top of each other, bore out your holes. Thread them through and add some spreaders to stop the batten sagging. Count yourself lucky you don't need to do a full cage: Edited February 5, 2017 by iSelfBuild 2 Link to comment Share on other sites More sharing options...
Russell griffiths Posted February 5, 2017 Share Posted February 5, 2017 1 hour ago, Vijay said: Cheers for the replies. I think timber supports would be a mammoth task as I have at least 437 L bars over 131 linear metres (300 spacing). Even using string would need a trial beforehand I reckon as some of the spans are quite long and I'd imagine the string/cable would need supporting. What would the max span the support string/cable could be stretched too, holding L bars every 300mm without dipping? I think you are off the mark a bit here. The string is to keep them upright until the concrete starts to harden it is not to support them. It looks on your drawing that there is no reo in the trench so that means there is nothing to tie the starter bars to. I would mass fill my trench and level it, go and have a cup of tea and a biscuit, you will start to feel that the concrete is getting firm. Grab a bar that you have already pre marked with the insertion depth on it, plunge it in the concrete and wiggle up and down push down to desired depth and let go. What happens next. Answers on a postcard please. It falls over and gets covered in crud. Remedy. Go and have another tea and come back in ten minutes. It stands up on its own like a soldier outside Buckingham palace. Repeat436 times. Perfect. You cant push it in. Oh shit you shouldn't have had so many biscuits. Link to comment Share on other sites More sharing options...
jamiehamy Posted February 5, 2017 Share Posted February 5, 2017 3 hours ago, Vijay said: I think timber supports would be a mammoth task as I have at least 437 L bars over 131 linear metres (300 spacing). This my friend is going to be a recurring theme I'm afraid! Wait until you're making up H-rails! Remember you would prepare ALL the battons/timber before you even put rebar out - get them all done at the spacing and then fit in one operation. 437 sounds a lot but it's not going to be onerous and once you get into the swing, you'll fly through. You'll get the battons done in a morning and the rebar laid out then the timber fitted in a day. I wouldn't be putting anything in after the pour - you've got enough to be worrying about without that pressure. 1 Link to comment Share on other sites More sharing options...
Vijay Posted February 5, 2017 Author Share Posted February 5, 2017 I think the batten /timber idea could be the way to go but obviously if Russell is right, it would make life so much easier. I think it would make sense to speak to the concrete supplier to see what the window is for putting in the L bars or if timber battens is the way to go Link to comment Share on other sites More sharing options...
Vijay Posted February 5, 2017 Author Share Posted February 5, 2017 2 hours ago, Declan52 said: How are you putting the concrete into the trenchs , digger bucket, wheel barrow or pump?? Unless the steel is tied together if you tip a load of concrete into the trench it will tip the L bars over. Could you buy some lengths of 5mm bar and put a strip at the bottom and top so you end up with maybe a 2m long bit of steel cage that will be much quicker to drop in during the pour. The top length of 10mm can be reused if needs be. This is how I seen it being done on a ring beam. The plan is to use my new (old) 2.5t dumper and drop the concrete into the trench. It'll be all hands on deck to spread the concrete and I've got a concrete vibrator as well Link to comment Share on other sites More sharing options...
Vijay Posted February 6, 2017 Author Share Posted February 6, 2017 Called round for concrete prices today and asked a few potential suppliers about the L bars. They all said the same thing as Russell and say there's no exact time before it sets off as it depends on things like weather conditions and temps, but basically I have about a 2 hour window before the concrete isn't gonna like being disturbed. On 05/02/2017 at 19:19, Russell griffiths said: I think you are off the mark a bit here. The string is to keep them upright until the concrete starts to harden it is not to support them. It looks on your drawing that there is no reo in the trench so that means there is nothing to tie the starter bars to. I would mass fill my trench and level it, go and have a cup of tea and a biscuit, you will start to feel that the concrete is getting firm. Grab a bar that you have already pre marked with the insertion depth on it, plunge it in the concrete and wiggle up and down push down to desired depth and let go. What happens next. Answers on a postcard please. It falls over and gets covered in crud. Remedy. Go and have another tea and come back in ten minutes. It stands up on its own like a soldier outside Buckingham palace. Repeat436 times. Perfect. You cant push it in. Oh shit you shouldn't have had so many biscuits. Link to comment Share on other sites More sharing options...
Russell griffiths Posted February 7, 2017 Share Posted February 7, 2017 A couple of things to think about if you lack a bit of concrete experience this is is not an afternoon job. Get the first truck on site at 8.30 am then the second straight after do not be ordering it for 11am you need to get it n quick smart rush about like a madman and then have a breather as you will need your 2 hour hardening window to get all your bars in. Be prepared. Get all your bars and spray a line on them for insertion depth, mark a fill line around your trench. Make yourself a tamping thingy make sure the dumper has diesel get a tarp ready for the road or driveway make sure you have batteries in your laser if you have one. Good luck. Link to comment Share on other sites More sharing options...
Vijay Posted February 9, 2017 Author Share Posted February 9, 2017 Cheers Russell. My plan is to start as soon as they do their first delivery. I believe I will have 8-9 concrete deliveries for the 65 odd m3 of concrete, The dumper is 2.5t so planning on 4 safe skips of concrete per delivery to empty the concrete truck. So I'm thinking of deliveries every 1/2 hour, then we'll have time for a break before doing the bars (while I keep testing cos my balls ain't big enough to risk it lol) There should be at least 4 of us (one on the dumper), so 3 tampering and then all 4 doing the L bars. Is a "tampering thingy" just a large T made out of wood, 600mm wide for the width of the foundations? Link to comment Share on other sites More sharing options...
PeterW Posted February 9, 2017 Share Posted February 9, 2017 Why are you using the dumper ..?? Can the concrete wagon not get to two reasonably separated points on the foundations ..?? If you go for a self leveling concrete then 65 CuM will go in from 8 loads which will easily pour inside 2 hours as long as you've got two pour points. It also means it won't have time to start curing as 4 hours will mean you could get dry joints appearing. Link to comment Share on other sites More sharing options...
Vijay Posted February 9, 2017 Author Share Posted February 9, 2017 Not really, can only get along the front of the trench. That's why we planned to used the dumper which will get around everywhere Link to comment Share on other sites More sharing options...
PeterW Posted February 9, 2017 Share Posted February 9, 2017 For the hassle factor and for speed - which with 65 cube you're going to need - I would dig a 300 trench across the left of the P of plot and put in at the corner of the garage and the other corner of the house. That's going to be one heck of a pour..!!! Link to comment Share on other sites More sharing options...
Vijay Posted February 9, 2017 Author Share Posted February 9, 2017 This is the actual layout of the trenches (for all external, internal and sleeper walls). So would the concrete easily flow everywhere????? 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