Thread: Advice for trellis

Pretty much dead straight along the fence. The fence itself isn't straight, which is part of the reason to screen it, but I can easily make the trellis straight. The only complication is that the block is on a slope, so the trellis will be in 3 staggered sections. This should actually provide some strength when it comes to tensioning the wires since they will be working against each other in 2 places.

Thats a big sail you got there. The wire will try and pull the fence straight.
Stuart

Originally Posted by Stustoys

Thats a big sail you got there. The wire will try and pull the fence straight.
Stuart

Not sure what you mean there - the trellis will be free-standing - about a foot or two from the fence. The fence is straight as in vertical, but not aligned straight. It hops left and right either side of a staggered retaining wall, kind of like below, but not quite so neat. The trellis is the straight dashed line under the top line.

_____/------\__/----\_______
------|--------------|--------

The breaks in the bottom line are where the trellis will be staggered - so we have 3 sections. Again, just a very rough picture. The far right is ground level, the next is a 0.5m height difference, and the far left section is another 0.5m height difference. So a wire strung between the very top of the middle section will pull that section's outer posts inwards. Wires strung at the top of the other two sections will pull those same posts outwards. So I really only still have to worry about strengthening the two outer posts. But I might do the lot anyway.

oops "fence" should read "trellis"
"The wire will try and pull the trellis straight" If it isnt straight already.
my head hurts i'm going out to play in the shed lol
Stuart

Just a quick question regarding timber cross pieces....

Will 2.4m spans of 140x35mm dressed pine sag or warp? I have a lot of it lying around so that would be best to use. If it will sag, I'll have to look at an alternative.

Instead of cross pieces I would use guy wires on the end posts to keep them upright and resist the load... All you need then is another concrete footing a meter or so from the end post, then run a cable on an angle to the top of the end post. If you are also going to tension up all the wires in the middle and you notice the posts bending in the middle you can also have a second wire running to the middle of the post.

Also there is special primer available for galv steel.

Originally Posted by gallegos

Instead of cross pieces I would use guy wires on the end posts to keep them upright and resist the load... All you need then is another concrete footing a meter or so from the end post, then run a cable on an angle to the top of the end post. If you are also going to tension up all the wires in the middle and you notice the posts bending in the middle you can also have a second wire running to the middle of the post.

Also there is special primer available for galv steel.

This sounds like a good option. I see this arrangement used at vineyards. What gauge of wire do you suggest I use?

Also, I was only going to use 2 or 3 bags of rapidset per post. This is starting to seem a little stingy. Should I double the dosage to 4 or 5 bags for the sake of $100? Holes will be 1500x300mm, which is about 0.1 cubes. 20kg of rapidset makes 1/10th that amount, but I wasn't planning on completely filling the holes. Is there a guideline on this type of thing?

2.5mm high tensile wire is commonly available for rural fencing but you probably don't want 1500m of it. You can also get larger dia soft wire which is a lot easier to work with but they place below doesn't seem to sell it. At bunnings they seem extortionate for the small rolls of wire so probably worth looking somewhere that does rural supplies to compare.

Plain Wire

I think the biggest thing you will find with wire is that you will want a good way to tension it if you want to end up with nice straight tight stands. This will probably be quite difficult on a short run like this because a little bit movement will see it go slack... its a lot more forgiving on long stretches.

If you are going to put the posts in 1.5m deep you could probably get away without any concrete and you probably find the RHS bends before it falls over. I built a trellis once by hammering 25mm RHS into the perth sand as far as I could and I never had a problem... obviously wasn't 3m high though More of an issue will be the corrosion I think especially with electro coat as its quite a thin coating. Casting in concrete will protect it but you generally only need 50mm of cover to protect cast in steel. You also need to make sure where the post comes out of the concrete that its above the soil otherwise the post will just corrode there. If you can dig a 150mm hole 1.5 m deep that would be enough I think and would save you a heap of money and labor mixing concrete.

Hi, I stumbled upon this thread from Google, and I am contemplating exactly the same project for a grape trellis along my fence, with almost exactly the same dimensions!

Any follow up on how your project went? Especially what you did to secure the end posts. Photos would be nice!

Thanks.

Just a suggestion,use normal concrete not rapid set,if you don't get the mix of that stuff right it will be no better than rammed earth.
It is not recommended for structural use ,normal cost the same anyway,wait till next day to fix to and you will end up with a better job and won't take any longer to do.
You can save on the amount of concrete you use by putting some at the base of your post (about 200mm),filling with earth,ramming down then having a second lot at the top again about 200mm.
Done many posts like this with good results.

Originally Posted by nayler

Rust or rot - which will come into play first? .

I would personally stick with gal steel, I believe it would see you out. As for treated pine, it won't rot, but it still weathers, ie spilts, cracks etc.

Almost 2 years and project still isn't done. So many other things have taken precedence - chook pen (also unfinished), front lawn (looking awesome), plasterboarding inside of shed (also looking awesome), new floors in house + internal wall modifications (also looking awesome). The trellis just took a back seat.

I've bought 11x 6m galv lengths - they are just lying on a frame I knocked up next to the fence. I was planning on a building a series of H frames and then stringing them together with wire.

Hi Nayler,
Just a few thoughts on your trellis. I recently put 3 wires on a carport to support a vine. The posts are 100mm square with 6mm walls, when I tensioned them the outer posts bent in at least 25 mm in the middle, so the forces are quite high. I used small (about 100mm long) turnbuckles for tensioning. I like the previous posters suggestion of concrete in the bottom of the hole, then packed earth & concrete for the last 300 mm or so. To brace the uprights I would use pipe between the posts & just drill a hole right through the posts & thread the wire through the hole, then through the pipe & through the other post. This wire could then be taken down at an angle (45 degrees?) & anchored. I would only use 2.5mm high tension wire from a rural supply. You could concrete a short angled post out from the trellis ends if you have room & anchor you wires with turnbuckles near ground level, (both ends would be good) A small bush planted there would hide & protect them & you. I would not use rapid set concrete.
Ian.

I would agree with Ian. Takes a lot of force to tension wires. I have a bit of rural fencing experience. I have heard that treated pine does not like contact with cement. I don't exactly know why. Steel is ok but thin stuff will rust fast so make sure to close the top and protect the bottom. My preference would be for a treated pine timber top rail and except a little sag in the wire from other points. The vine will cover it. The other method would be some sort of mesh whether weld or chicken or even cyclone. With the top bar the use of mesh will vastly reduce the sag.

I am putting up a verandah. We have some mesh bought for putting under clear roof sheet by my step son and not used. We are going to put it along the end of the verandah when finished to hide stuff behind it.

Dean