Shuttering for circular patio base.

[silly_savage]

Can anyone advise on the best sheet material for forming a 2.8m circle to form a concrete base for a patio. In truth it will actually be ring, essentially a small retaining wall which I can fill with sub-base, so a 2.4m diameter form inside the 2.8m, 100mm above the current grade and about 150mm below without having accurately checked my levels yet.

My reason for not just doing a whole circular base is that I want a permeable patio to avoid water logging in the remaining garden, so will use a permeable bedding course and polymetric sand for joints. I have never built anything out of bricks so this seems the best route rather than building the edge up from a footing. The ring will be capped by decorative edging pavers and backfilled with soil for flowerbeds.

Would a 5.5mm ply survive the load supported by stakes and partially supported by the ground? It'll be about 0.4 cubic metres of concrete going in to it in total.

Reusing the forms would be nice but not essential as I'll have another curved path edge to make in a similar vein.

 

[Mr diy a lot.]

6mm hardboard.

 

[silly_savage]

oh yeah? ok. I wondered if it would be flexible enough and strong enough, but I'll be happy if you're right as it's half the price.

 

[Mr diy a lot.]

If you give it sufficient structural support with pegs round inside and outside or braces in between inner and outer walls, maybe a few old breeze blocks etc to keep it al in shape and trowel in your concrete mix carefully it should be fine - it does not need to be pretty - you just want that concrete donut shape.

 

[Charlie George]

150mm upvc utility board is another option, and will also bend to a near perfect circle,and comes in upto 5m lengths.
https://www.directplastics.com/upvc-soffits/white-soffit-boards/9mm-white-flatboard/GMB150W

 

[silly_savage]

150mm upvc utility board is another option, and will also bend to a near perfect circle,and comes in upto 5m lengths.
https://www.directplastics.com/upvc-soffits/white-soffit-boards/9mm-white-flatboard/GMB150W

Cheers, yeah I thought about that, works out expensive, though they'd be reusable at least. Not sure I'd get enough use to make it worth the investment.

 

[Agile]

I would be inclined to make up a 1m section using thin ply or hardboard etc. Held in place by tacking onto a cut out curve shape on a 30mm or 25mm old plank.

Thus laying in 1m sections. Or making up a couple and laying in 2m sections.

 

[Munroast]

pack damp soil behind the hardboard, then after the concrete is poured it is easy to make minor adjustments to the roundness.