Week 10 - Shuttered Walls

Red Kite

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As you can see in the video this week they built up the shuttering in layers; first the outside, then the steel in the middle of the sandwich and finally the internal shutter.

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Also along the bottom they cleaned out the kicker and laid in a waterbar / waterstop (that brown bar in one of the photos) in a pre-formed channel, this forms a seal and prevents any water coming through the joint between the walls and the floor.

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They bolt the two halves of the shuttering together with steel threaded bars inside a foam sleeve so that they can get the right thickness and hold the shuttering against the weight of wet concrete. The steel bars come out when they strike the shuttering and they waterproof the holes. IMG_20191130_112653548_HDR.thumb.jpg.8f540e5b086cedefdaa7d148f47be002.jpg

 

As you can see they didn't pour all the walls in one go but built alternating sections and will do the infill next, I think this is partly down to cost  of shuttering hire, and partly down to the sheer weight of concrete. The steel shuttering is really solid and well braced so there is no risk of collapse or burst and wet concrete spilling out everywhere like you sometimes see on GD's.

 

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It was a bit of a wet week but they pushed on because the waterproof concrete and pump was booked for Friday, and they had extra manpower on site as my contractors brought in a couple of guys from the shuttering hire company who really do know how to put up shuttering fast! Sometimes it pays to get in the experts who do just one job really well. I had an interesting discussion that groundworks like this is often seen as a pure manual labour job rather than a skilled trade like sparks, brickies or chippies. In fact, at the level our guys work at, it is really a highly skilled trade and they are working to really fine detail and tolerance, plus you only ever get one shot at poured concrete! We have nothing but admiration for them - they are doing an amazing job in some pretty dreadful weather.

 

Next week they will take down the shuttering so we can really see the exact size and scale of the walls which will be great. Then they will rebuild the shuttering to make the remaining retaining walls and expect to pour these in about 10 days and this will be the last of the poured waterproof concrete - it will be great to get that done before it gets really cold as the waterproof needs at least 2 deg.

 

Progress on the other elements is crawling along; MBC seem to be taking an age to produce drawings, and Internorm should have the survey complete next week (so about 4 weeks) and are now saying 12 - 15 weeks for delivery - so March-ish. We could say that delays getting MBC drawings make this easier - MBC have not given an estimate of when we will have a frame on site but I am expecting its now into February-ish. And this will give the groundworkers plenty of time to complete the substructure if the weather turns really bad. After 5 years of delays with PP you tend to get a bit blasé about the odd few weeks and we have never had a rigid timescale but it is a bit frustrating how long some of these things take, and how little control you have! Almost certainly their relaxed attitude to timescales will not extend to payment terms!

 

 

See https://www.dropbox.com/sh/th9f6e3cel5dm1q/AAAfsWdAH184J75bCNUUtzVra?dl=0  for the weekly videos. The weather for the pour of the walls was dry and sunny,  but very high humidity give it that ghostly misty look - will try to get the next pour a bit clearer - I think the presence of a concrete pump upsets the camera somehow!

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Very similar approach to our build - sub-structure with MBC frame on top.

 

We also went with shuttered concrete - out team did all the steel work first then built the shuttering, they explained that the concrete needs to go off for a good few days before new concrete can be cast against it so we had a similar 'staggered' wall pour with 1m gaps between them which were poured last. You should have vertical water bar in these sections also.

 

Is the water bar channel full of water? Our guys were made to dry it out with a blow torch before using a mastic to hold the waterbar in place (Sika products) the rep, who issued the warranty, even came out to check this and they sent him photos every day from site.

 

They also used nifty expanding rubber plugs to seal the bracing holes, effectively a rubber bung on a thread that is screwed in to compress and expand the bung. Then cement to seal the hole. 

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Its really good to see the progress and how it all goes together.

 

One thought i have is the shuttering walls look very labour intensive, which i can imagine sends the costs up.

 

Did you consider pre-cast panels like below?

 

https://www.jpconcrete.co.uk/precast-cast-in-retaining-wall/

 

i am wondering if the materials may cost more, but in terms of labour it actually works out cheaper.

Edited by Moonshine

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1 hour ago, Moonshine said:

Its really good to see the progress and how it all goes together.

 

One thought i have is the shuttering walls look very labour intensive, which i can imagine sends the costs up.

 

Did you consider pre-cast panels like below?

 

https://www.jpconcrete.co.uk/precast-cast-in-retaining-wall/

 

i am wondering if the materials may cost more, but in terms of labour it actually works out cheaper.

 

Yes, formwork build & placement is quite labour intensive. 

 

With some thought, the same form can be reused on a build (depends on complexity of design) - for us, the shape of our basement allowed the contractor to build one pair of forms (inside and outside) that built a corner with a window and they were able to use it a few time before re-configuring it.

 

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Pre-cast is probably less labour and possibly cheaper materials, but I was not able to find a waterproof version so I never costed it out. If I had gone this way then I would have had to put external tanking (as I am doing now) and also an internal tanking / drainage membrane. You need two  of three, forms of waterproofing in habitable basements (external tanking, waterproof concrete, internal tanking/drainage). I have a real aversion to internal drainage as it seems like an admission of failure if you let the water in and then pump it out. The other two options were Glathaar (German offsite precast) that are eye wateringly expensive, plus they dont do the dig - just the panels. Or ICF which would have worked out well, but we have a very odd insulation setup that would have made it tricky. Plus I wanted to use our contractors and they are singularly unimpressed by ICF - though they are never very clear on why.  The waterproof concrete on its own in likely sufficient, especially as we are out of the ground at the front so have low hydrostatic pressure, and the external membrane is just another of those 'belt and braces' features to keep the BCO happy and give us a 20 year warranty.

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