Show us yer shuttering...

[Mulberry View]

I'm just debating getting the shuttering in place in my foundation trenches. I have a few to do, but the specific one that's concerning me is one where I have to have a 600mm step on a T-Junction. Instinct initially said to shutter on the face of the joining trench, but I'm now thinking of setting the shutter some way (perhaps 500mm) into the leg of the 'T'. My rationale is that it'll be easier to install the shutter there and will provide a decent infill gap between the step and the adjoining wall, instead of the very short piece I'll have to add if the step is right up to the adjoining trench wall.

 

Would a shutter holding back 600mm of concrete, say 500mm back from a corner be risky? Might it break the corner off the trench?

 

I hope my explanation makes some sense to someone! Also, what materials to use?

 

It would be helpful to see pictures of your shuttering for inspo.

[ProDave]

That is a big step.  I would do it in two 300mm steps, much more managable.

[saveasteading]

600mm is a lot of wet concrete to support and the shuttering would have to be very secure.

[Mulberry View]

5 minutes ago, ProDave said:

That is a big step.  I would do it in two 300mm steps, much more managable.

 

Fair point. I have 3 trenches that require this step, circled in red on this plan.

 

 

The main rectangular shape (the one with 3 sleeper walls) is 600mm lower than the adjoining building. You'll notice that one of the 3 adjoining trenches is rather close to a corner, so I'm not sure of the practicality of 2 steps. Maybe one would be before the corner and one after it?

 

We're on hard chalk, so apparently we don't have to think too much about overlaps.

[Dave Jones]

600 is doable, scaff planks cut tight into the sides make the best spiked wither side into the banks with rebar.

 

wont move.

[Miek]

8 hours ago, Mulberry View said:

We're on hard chalk

This makes it easier to make strong shuttering. Ideally get or make some steel stakes (square is best) , but if you only have wood then use that. 

[Mulberry View]

Thanks for your input.

 

Do I need to make the top of the shutter level with the top of concrete or does that not matter? Presumably the bottom of the shutter needs to be level with the top of the concrete in the adjoining trench?

 

I had the idea in my head that that concrete would flow under the shutter from the higher 'chamber' to the lower 'chamber and cause it to overflow. Does that not happen?

[ProDave]

If the concrete flows under the shutter then it if far too wet.

 

Our steps were small so the shuttering was very simple.

 

 

 

 

 

[Mulberry View]

17 minutes ago, ProDave said:

If the concrete flows under the shutter then it if far too wet.

 

Our steps were small so the shuttering was very simple.

 

 

 

 

 

 

It's a pump grade spec, going in with a boom pump. Will that mean its wetter?

 

Thanks for the pic, I'm assuming some element of your timber will be stuck in the concrete afterwards?

 

How far apart are the 2 steps in the top left of your pic? That's a similar arrangement to mine, though my steps will be bigger of course.

[markc]

Pumped will (should) not flow under a vertical shutter unless over poked to make it flow. When pouring a big slab with perimeter walls you do the perimeter of the slab first poking to flow under the shutter, then the middle to allow a few minutes settling and then pour the walls being careful not to over poke causing the slab to move.

so do your low level pours first then go back and pour the higher sections allowing the mix to flow up to the shutter.

[Mulberry View]

I'm planning to sort the shuttering today/tomorrow. No doubt I'll overkill that, it's just my way! I assume 18mm Ply/OSB or Chipboard will do fine?

 

As far as depth goes, I'm thinking of banging lengths of rebar into the bottom of the trench to gauge the top of concrete. Some suggest leaving the rebar long so as not to lose it in the concrete. I'll get some 12mm rebar for this and thinking around 2m spacing. Any other pointers there would help.

 

I do have a good rotary level and am planning to make a staff up to measure the top of concrete.

 

Getting the concrete in and right will be a HUUUUGE relief for me, it's been a very stressful few weeks after this whole nightmare episode.

[markc]

Found pour levels often done with rods/rebar/big nails pushed into trench sides (on a site vertical rebars in trench would be classed as a hazard and need caps.

[Mulberry View]

1 minute ago, markc said:

Found pour levels often done with rods/rebar/big nails pushed into trench sides (on a site vertical rebars in trench would be classed as a hazard and need caps.

 

I can put caps on them.

[Mulberry View]

I can't get my head around the notion that this shuttering will work.

 

In this example, the shutter is set up so that the bottom edge is the level of the concrete in the adjoining trench on the other side of the shutter. On the nearside, the step is 600mm (for reference, there is a line of screws that denote the level,  it's about 300mm down from the top of the board). As the concrete can flow under the shutter, will the large head of concrete on this side of the shutter not influence the level on the low side?

 

 

 

 

Here's another example. The concrete on the nearside is about 400mm deep and will be level with the underside of the shutter, on the far side, the level rises to 125mm higher, but not quite to the top of the shutter.

 

 

 

I'm the king of overthinking. Pour day is tomorrow, I need to be able to sleep tonight knowing my shutters will work.

[Canski]

Looks fine. When you pour put some against the shutters first to close the gap then move on somewhere else in the foundation. Come back to it later and it should have gone off enough to fill it up. ( as long as your shutters hold)

[Mulberry View]

Baffling, but thanks.

 

I really hope the shutters hold. 🤣 

[saveasteading]

In theory that can work, but beware  the ready-mix driver just pouring it fast and hard, as the force from fast moving concrete is huge.

That apples especially where the fixing pin is near the trench edge.

 

Safer to have it poured into the trenches away from the shutter then shifting it along, with similar pressures both sides.

 

Prepare for the worst and it should be an anti-climax, which is what we want.

[Miek]

With a boom pump you will be fine as long as the operator is good, they do this day in day out, they will know how to avoid breaking the shuttering. 

[Canski]

I would put another timber on shutter 2 though

 

[saveasteading]

Just now, Miek said:

as long as the operator is good

Prepare for the worst, assume he is not good, and the weather is foul.

There is often a reluctance to tell a tradesperson 'how to do their job'. tell him you are nervous about the shuttering (ie your skills not his) and ask if there is a way of protecting it and he will possibly be patronising, but all will be well.

[Mulberry View]

1 hour ago, Miek said:

With a boom pump you will be fine as long as the operator is good, they do this day in day out, they will know how to avoid breaking the shuttering. 

 

That's what I want to hear. I'm super stressed about this, it's been a rough 4 weeks getting to this point.

 

I'm trying to get my head around how to know how much more to order towards the end. I've done precise trench calculations, that got me to just under 42m3, I have 43m3 ordered and apparently they've allowed for some part loads (whatever that means). I can't imagine we'll come in under, some of the trenches are a little on the wide side. But once we get into the latter stages, how do you estimate how much more to have loaded?

 

I'm hoping they'll leave my Carport until last, that's a rectangular shape, with a total of 7.5m3 in it according to my estimate, it'll be easier to figure how much more we need as that area fills up. Trouble is, that's the furthest away from the pump, so I bet they'll want to do it first!

 

I've got a couple of IBC's cut in half for the washout of the trucks and the pump (4 halves in total). I also have a couple of timber crates that we've lined with plastic to give them somewhere to dump any leftovers (but I think they'll only hold a cube tops).

 

I've got myself and my Brother on site, my Father-in-Law as backup help and SWMBO to organise the concrete trucks as these will not be in our line of sight. I've made my laser staff and a timber tamping frame. We have 2 hefty tarmac rakes, spades/shovels and 2 wheelbarrows. We've sprayed guide marks on the sides of the trenches for a depth guide.

 

Anything I've missed?

[Miek]

You've clearly put thought into it, that's all you need to do. 

 

The boom will do all the work, you will hardly need a rake. Remember it's just footings, they don't have to be pretty. I used a boom on my footings and just stood around and watched the operator and had a chat, took photos. 

 

Part loads are when the mixer is not full ( usually 8m for a big lorry) so the cost is a bit higher but don't sweat , just keep an eye on the quantity towards the end of the pour and adjust as needed. 

 

 

[TonyT]

Hope you have an area set

aside for wash down of the chute etc?

 

just

so they can clean up before leaving site

[Mulberry View]

13 minutes ago, TonyT said:

Hope you have an area set

aside for wash down of the chute etc?

 

just

so they can clean up before leaving site

 

Yes, I covered that in a post just above this one. I have some plastic sheeting to put down in the clean-up area, as it's not our land.

[PeterW]

45 minutes ago, Mulberry View said:

 

Yes, I covered that in a post just above this one. I have some plastic sheeting to put down in the clean-up area, as it's not our land.

It will run off … get some old scaff boards and make a frame and line with decent DPM. When the washout has started to set then go out with a sledgehammer and break it up.. imagine it’s your favorite planner / architect / mother in law etc …