Trench and Reo for fence foundation

[peterjs]

hi folks

I'm digging the foundation for our new front fence. The fench will be small - in the style of 1m high pillars with low wall between and metal spears. I reckon I might brick and render it. So the brick pillars will be only 2 bricks in size and 12 bricks high, with the low walls between as single rows of 4 bricks high. (I did say small).

My question is regards the foundation. There are many small fences in our area that are leaning over - that would be poor foundations right? We are in clarence gardens adelaide SA with lots of clay...

I'm finishing a trench that will be say 400 wide by 400 deep. (Most of the trench was dug the day I hired a dingo trench digger - that was fun . Also planning to put in some reo top and bottom when the concrete is poured, plus a track for the sliding gate.
Can anyone suggest a suitable trench size and reo for top and bottom?

[johnc]

Locally you need a building permit for a brick fence with footings, so your first stop should be a call to the local council to find out if a permit is needed and recommended size. Trench mesh is a god idea although for that height doubling up might be overkill, but hten mesh is cheapish so why not. I would of thought 400mm plenty wide enough and about 300 deep, but it depends on soil type, for long thin footings it is not a bad idea to err on the overdone side of things.

[peterjs]

Thanks John
I phoned council last week and they said permit only required for masonary fence over 1 m so I will stay under that - it is a small fence.

A local fencing material supplier said they might use 3 x 16 mm reo top and bottom in a 500 deep trench but I thought that might be overkill...

[ozwinner]

Most brickwork failure is due to poor foundations.

And I would put 2 rows of mesh.

Al

[peterjs]

Thanks for the advice folks. The fence has grown, the council has been contacted.

Now that the fence is gunna be 1.6m high the plans for the foundations have gone in to council, showing a trench that is 400 deep and 350 wide over the entire 16.8m frontage, with 400x400 by 800 deep holes for each of the five pillars. It will have 6 x 16mm rods along the entire length, 3 top and 3 bottom on 65mm chairs and top supported by ligatures.

There will be a 5m opening for the sliding gate, using 2 sections of 5.8m long sliding gate tracks embedded in the concrete, cut shorter as required.

Now my question is how to deal with the slight slope in the frontage: about 150mm over 16.8m according to the dumpy level.

I'm trying to set up some formwork so the top edge of the foundations is neat, so my question is: Do I try to set the formwork dead level, which means the foundations will be underground at the high end (driveway is at the low end), or step the foundations in say two places by 75mm each step or just follow the natural slope.

I feel like follow the natural slope is the preferred solution, but then I worry about the concrete tending to slump downhill before it sets up. Can I ignore this concern?

The fence will have to slide up hill, but such a slight slope shouldn't be too much of a problem...

From an earlier thread it sounds like once the formwork, plastic and reo is in place (plus a bit of conduit for the gate motor) we can call the concrete truck and they will fill the trench while i play with the mix to try to make it follow the formwork. Sounds like an adventure to me...

[joe greiner]

Slope of about one percent should present no problem in following the formwork. More important is to work the concrete (vibrator, shovel, etc.) to make sure it completely fills the form and fully encases the reo. A good mix shouldn't be so wet that it would do all that by itself.

Joe

[ozwinner]

Formwork?

Arent you you just putting the concrete into the ground?

Start at the lower end of the block and set some pegs into the side of the trench so that the concrete for a given run is level and doesnt come out of the ground.

Step up for the next run by 86mm or multiples of 86mm, this will keep the bricklayer happy.

You need to do this well in advance of the concrete truck arriving.

Al

[joe greiner]

It'll look better if the top of the foundation is buried, and like Al says, you won't need formwork for the wall footing itself. The footing at the driveway gap should probably be flush with the grade, though, and a cross wall form would be needed to form steps on both sides of the gap. Side forms would also provide a neater product here. Even if the driveway gap is quite distant from the middle of the fence, it's probably easier to just make each portion of the fence footing level (as well as the top of the fence); might have a few excess buried bricks, but still simpler than stepping the footing (except, as I said, at the driveway gap). [Note that your total drop of 150mm is less than 2 x 86.]

Now, back to the footing at the gate: You'll need an extension of the flush-with-grade footing on each side of the driveway gap to support the track. Easier to do these later, with a bag or so of DIY concrete mix, than trying to form it all in one go. Put some bent bars in the fence footing to anchor the extensions. Surface-mount gate tracks would be more effective than trying to embed the whole thing (in what?) A picture/sketch with exaggerated vertical scale would help in planning your work. You probably don't have enough volume in the (1) fence footings, and (2) gate footing, to justify two separate deliveries except at substantial premium cost. But check with your concrete supplier anyway; might be easier that way.

Joe