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Posted: Mon Aug 31, 2009 2:39 pm
by Ramsey
Hi,
I have a set of formwork steps that have been built ready for the concrete to be poured. They have been properly reinforced etc to withstand the weight, but I have a few questions please:
1. Should I use plastic membrane under the concrete (not on the engineers drawing, but thought I would ask)
2. Engineer specifies two layers of a252 mesh be used with 50mm cover to all reinforcement. What is used to seperate the mesh and to raise it off the ground? I gather using bricks to prop them up etc before pouring the concrete is not acceptable.
3. Does the meshwork need 'tying' together and if so what is used to do this?
4. What is the best 'process' of placing the concrete? I will need to hire a concrete pump as they are a big set of steps over 15 metres long. I gather that it is best to start from the bottom step and work your way up, but would appreciate any help or tips in this regard.
5. When leveling each step after pouring, do I just use a spare piece of rebar to ensure the concrete has reached the bottom of each step and to get rid of air bubbles etc and then trowel the top surface.
6. Also, having never used a concrete pump before, is there anything that I need to know or will the driver help. I have heard of horror stories and am a bit wary of them.
I might have a few other questions as well - I'm just worried that it could end up with a lot of concrete all over the place!
Thanks for any help,
Rams 
Posted: Mon Aug 31, 2009 3:06 pm
by lutonlagerlout
normally we use bits of broken council slabs ,I am sure you can get special spacers but i have only seen these on big sites, you use tiewire to tie the rebar together,you need a pair of snips for this
the concrete pumps are ok but you will need safety glasses,as the stuff can come out with some force and spit back up into your face,TBH i dont like them,a lot of people have been killed and maimed by them,but if you got to use them so be it
and you need a concrete poker to vibrate the concrete and ensure no air is trapped.
as for DPM its up to the engineer really
hope this helps
LLL
Posted: Mon Aug 31, 2009 3:15 pm
by GB_Groundworks
are they garden steps or in a house thats being built?
not to sound patronising but you sound like you don't know much about concrete and steel fixing, have you thought about letting pro's do it rather than making a balls up of it.
a concrete pump might be overkill yes its 15m long but i bet there is only a couple of m3 of concrete in it.
a pump is likely to set you back £450 for the day plus you loose nearly a .5m3 in the pump, and they are dangerous and not really for diy'ers.
also maybe its a bit late now but we buy all our concrete stair cases pre cast from drawings and just crane them in, so much quicker and easier than going the shutter route like we used to.
1. depends if its a staircase in a house then no but if its sitting on the ground then yes, you'll need to release oil the shutter before pouring teh concrete
2. you get towers from the rebar company at different heights and a roll of tying wire, cut and twist it with end nose cutters.
3. yes, mild steel tying wire
4. again depends on access, if you have a few of you use buckets. or if you have a machine on site use the bucket of that. etc
5. hire yourself a small battery powered vibrating poker, i wouldn't use a large petrol poker as it might shake your shutter to pieces.
we have one of these http://www.suresafe.co.uk/makita-....68.html
6. they are strong and pulse alot, never use a piece of rope tied to the end, never. if your working with a hiab one as opposed to one lay on the ground don't try and fight or it'll put you in the concrete or worse.
finally make sure all your skin is covered and you have proper safety glasses on, concrete pumps spit concrete all over the show and it get every where and burns. get your self some disposable paper overalls like the crime scene lads wear them and just chucks them. gloves and other ppe essential
gi
Edited By GB_Groundworks on 1251728713
Posted: Mon Aug 31, 2009 3:52 pm
by Ramsey
Thanks for the replies.
They are garden steps up a steep bank.
Thinking about it, I might use buckets to place the concrete (not very keen using a pump) but will have to see how long the lorry will be willing to stay.
Posted: Mon Aug 31, 2009 3:55 pm
by Ramsey
p.s. GB_Groundworks, I don't know very much about concrete and steel fixing as you say, but unless there are any professionals that will work for free/cups of tea then I don't really have a choice! Thanks for your help so far.
Any further tips are much appreciated.
Posted: Mon Aug 31, 2009 4:04 pm
by seanandruby
Did you blind the sub base with concrete first, if not then a membrane will be good. broken flags will be fine unless you are going to see the underside of the stairs. I am assuming they are garden steps, or simular, because of the length. are you using a static pump, or mobile pump? A mobile pump will be able to put it where you want by dangling the delivery pipe above your steps. you will need to be fast, dont over poker, a quick dip down to the bottom of each step in every 450/500ml, otherwise you will keep losing the concrete in the step below. don,t hang around as steps are notoriously quick in going off. Keep chucking the surplus up to the next step as you progress. I use a small rip of ply to scrape off the excess concrete. have a man follow you levelling and plastic, or wooden floating as you go up, then metal trowel as you come down. keep the timber treads, risers, strings etc as clean as you can its easier to trowel that way. also dont push the edge of the trowel under the ply riser to deep or you will have an unsightly trowel mark on each of the concrete risers when you strike the shutter. Remember quick and clean :;):
Posted: Mon Aug 31, 2009 10:13 pm
by lutonlagerlout
for this i would use barrowmix,you can get a lot of man hours for £450 of pump and as giles said the last half metre stays in the pump till the driver spreads it over the road 
if you use barrowmix, easymix, or mixamate in your area then you will need 1 guy pushing , 1 filling the small gorilla buckets (these work better than rigid ones) and one pouring and vibrating
its very important you get the slump right,too wet and it wont hold its shape ,too dry and it will be full of holes
LLL