# Forum Home Renovation Concreting  Flexible formwork

## sundancewfs

I am going to pour a circle of concrete, for a paving base, for a clothesline area and I'm wondering what is used to make curved (circle) formwork. the circle will be 2.4m diameter. I will also have a 4.5m diameter circle to pour for a tank base soon.

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## SilentButDeadly

we used to use offcuts of laminex....

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## sundancewfs

Thats not a bad idea...
Do you have to support it with a multitude of pegs? If so what size do you use?

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## droog

My previous effforts for curved formwork have been with strips of masonite. And yes many pegs dependant on the shape and size.. 
Regards Dave

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## Metung

I did a 1.8m diameter X300mm high tank stand and used that thin (2-3mm) mdf type board with star picket stakes every 400mm. Damn thing still bulged between the stakes. Something like Laminex which is a bit stiffer would probably have been a better optoin. I just had the idea that maybe 2 or three light ropes around the outside before staking might have been the go.

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## TermiMonster

If you can get your hands on a sheet of old ply, about 9mm, rip it to the width you need, you can bend it , use a fair few stakes, and it shouldn't bulge.  Old laminex is a good idea too.  You can use timber (if that is all you have) by putting cuts into one side, so it will bend, but not so deep that it will break.  Does that make sense.
TM

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## Cementer

> I am going to pour a circle of concrete, for a paving base, for a clothesline area and I'm wondering what is used to make curved (circle) formwork. the circle will be 2.4m diameter. I will also have a 4.5m diameter circle to pour for a tank base soon.

  
MDF skirting board (the one thats painted white) works quite well and dirt cheap too. If a tight circle is needed then give it a light soak in water. We used to throw it in the pool for or in the gutter with a hose for half hour. Any longer and it disintergrates.
Yes, many pegs required. Size depends on how solid the ground is.

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## sundancewfs

> MDF skirting board (the one thats painted white) works quite well and dirt cheap too. If a tight circle is needed then give it a light soak in water. We used to throw it in the pool for or in the gutter with a hose for half hour. Any longer and it disintergrates.
> Yes, many pegs required. Size depends on how solid the ground is.

  I was at Allcrete in Bayswater today and asked them what to use, they all turned to a customer who was in the shop at the same time, thats exactly what he suggested. He is now going to give me a quote on doing our house and shed slabs too. (2 slabs approx 8x8m each with 54 bored piers 450mm x ~2.5m deep, shared between the two, beams and 100mm slab) Don't you just love "P" class soil...... :No:

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## Eastwing

> Don't you just love "P" class soil......

  No but Geotecs do, I sometimes get a second soil report (from another company). there are a few companies that rate every site P (no risk to them) unless you get lots of soil reports done in a year you would never notice. Sometimes it's worth the extra money for a second opinion. Send me a PM if you want a report from a company that uses more than one letter in the alphabet.

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## Ronaldo451

_I just had the idea that maybe 2 or three light ropes around the outside before staking might have been the go_ 
Metung....brilliant!!   I have always just used masonite or ply with many pegs. Obviously the pegs are to hold the shape,not fix it to the ground as the weight of the mix will do that. If a few lengths of strapping or webbing (tie downs, seat belt material or whatever) was wrapped around the outside the formwork must stay in shape...brilliant

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## Cementer

> Obviously the pegs are to hold the shape,not fix it to the ground as the weight of the mix will do that.

  I don't want to stray from the original post but be careful about the pegs only holding shape. I have had formwork float before and believe me, if it does it creates a hell of a mess. Not to mention incorrect levels. Always nail off at least every second peg. The nails are cheap enough.

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## sundancewfs

I think I'll use the MDF and a lot of pegs.... nailed.
I seem to remember the guys that poured one of the tanks on our farm used a few 1/2" rods as strapping (bolted together at the ends) to hold the formwork in place

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## Terrian

> I was at Allcrete in Bayswater today and asked them what to use, they all turned to a customer who was in the shop at the same time, thats exactly what he suggested.

  gotta love it when something like that happens  :Smilie:  
btw, I have used 3" garden edging timber in the past, lots of stakes needed though.

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## BanPC

My concretors use a plastic flexible system from Conform in Brisbane. 
Their site is www.con-form.com.au, pretty sure you can get it through Mitre 10.   
.

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## sundancewfs

I did the job today
I used  110x19mm primed MDF  it was a bit tight getting it to fit a 2.5m diameter circle. It did work though. I held it in place with about sixteen 90x45mm pegs about 400mm long. I hammered them in about 300mm and then screwed the MDF to the pegs, leveled it up with the laser, put in the mesh and poured it. All up, it took 18 mixes of my mixer. (9 bags of cement, half a bag per mix at 3:2:1)

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