Due to digging and landscaping I need to put up fence posts in a bit of ground that is currently about 200mm below where it. It will be backfilled to the level where it will form part of a walkway, with gravel on top – so nothing’s going to be grown in it (hopefully, at least). I want to put fence posts in this bit using post holders, and the ones I have are about 200mm deep. So if I backfilled the ground then dug another hole to put the fence posts in then most of it will be in the backfilled soil and I’m worried it won’t be solid enough.

My options are:

1. Get one of those longer pointy post holders, whack that into the ground and concrete around the base of it

2. Plonk the post holders I have on the current ground level, concrete around it and whack dirt around it whilst it’s still damp.

3. Something else

What would STW do? The ground I have is clay with shitloads of stones in it.

If your posts are going to be buried I would use concrete posts as a wooden post will rot. If you’re backfilling to create a level, then concrete gravel boards between the posts are ideal – they also make keeping a level and line easier. They are heavy and can be a sod to get in place – a post hole spade and a big pry bar really help. I’ll raise you soil with rocks to barely an inch of soil with a solid 12” shelf or rock – I removed 6 barrow loads of rocks to dig a 3m x 300mm trench to plant a hedge.

I’d opt for 1.

As said, posts rot, and once they start to go, they lose all strength and are prone to snapping in strong winds. Steel sockets while unsightly are far more robust.

The posts won’t be in the ground, I’m using post holders for exactly this reason. It’s these that I want to concrete in place.

Theres a few different styles of metpost or similar makes. The spikey ones arw for hammering into solid ground. What i think you’re describing is new ground which will be quite loose?

How much work do you want/be arsed to do? I’ve done similar to this for (admittedly only 1) a post: dug down a foot or so and then sunk a piece of corrugated 300mm water pipe on its end in the hole sticking above the ground by another foot. Filled it with concrete and set some threaded bar in it for post holders to bolt a wooden post to. It eventually got back filled around the pipe the remaining foot so the ground is back level.

Edit: just for clarity I had all the material,  mixer and a spare afternoon to do it.

you can get lots of types of post mounts, look on screwfix. I’ve used both the ones you concrete in (funny square bit on the base) and the ones you bolt to concrete. both worked perfect. trying to hammer in a pointy one didn’t work well. I’d avoid.

Durapost are currently being installed chez Sandwich. 115mm diameter holes with a one man post hole boring machine and post fix has been a quick-ish job.
The chap who removed the old concrete posts recommended a product similar to cinterproof for wooden posts in concrete. 25 year guarantee against rot. Will ask what it is tomorrow when he returns.

Grow a hedge?

I don’t think you said, how high will the fence be?

180cm high

I hadn’t though of using bolt on feet. That might make life shitloads easier as I could just lay a chunk of concrete.

180 sounds quite a height for bolt on supports. I’d bury a spike.

That might make life shitloads easier as I could just lay a chunk of concrete.

I’d beware of laying in a trench, filling it with concrete and bolting said mounts to that. The entire thing could topple over, earth not really providing much in the way of support. Even if its a pad you lay in, i should think it would have to be in quite deep for the same reason.

So those points, a spike in a hole filled with concrete, concrete being in deep enough to provide a firm footing.

How long do you want to love there. Those Screwfix metal things are awful. Monkey metal barely welded together. Replaced dozens of them over the years, some of them a few years old. One big gale and they are down. Get some made out of much thicker steel by your local blacksmith/fabricator.

I’m assuming that you want a wooden post; simplest would be concrete repair spurs. Buy the 1200mm version and sink roughly 600 below solid ground. Position them to hide the spur if poss.
Either steel or wood in the ground will fail eventually unless you use spendy materials

I’m with timba. Or use oak posts. Most of those met post things are rubbish. You cant seem to get a hammer in metpost as long as the length of post you’d bury in the ground. They don’t ever look strong enough for a 180cm high fence.

earth not really providing much in the way of support.

Well that’s exactly the issue. But if I go deep enough it will be into the solid ground which is very solid. And when I say solid, I mean the local “soil” which is actually glacial till with about 50% rocks.

The fence is going to be picket style with 50% space so the wind load will be less. And I’m not planning on living here that long 🙂

How longs that long? I’d just use treated timber softwood posts dug in deep and rammed tight in that case. Especially if you’ve got rocky soil. You’ll need a shuv holder to not create too much of a hole.

I replaced a load of fencing last summer. I painted bitumen onto the bottom 2-3 ft of each post (some were longer than others for a pergola) to protect against rot. Dug holes to the relevant depth plus another 100mm or so for gravel to encourage drainage, popped posts in, filled with postcrete. I also haunched the postcrete to disperse rainwater as much as possible.

I did exactly the same as @spacemonkey on all counts, though they were for a shed/deck. Actually used a tin of waxoyl I found in the garage that I was probably never going to use on a car, thinned with white spirit. Obviously can’t say how long they’ll last, but they’ve got a fighting chance.

I need to replace some fencing from the storms. I was trying to think of an alternative to timber posts, but I don’t like the look of concrete, and it’s expensive. Come to the conclusion that timber posts treated as above will easily last until we come to sell the house, so will probably just go for that.

The ‘long pointy post holders’ / met posts are really for banging into soil. They’re pretty solid once in and unless you have accidic soil will outlast posts direct into the ground with postcrete. Concrete absolutely not needed. If you are in S. Wales then likely clay soil which they work well. Worth buying the plastic thingy that you drop in to allow sledge hammering. I’ve found them to be as strong as or stronger than concreted in wood post and faster than hole digging. YMMV.
You do need to be sure that there are no pipes, drains etc. to puncture.
If using concrete then cast in or bolt on steel post base is probably a better bet.
N.B. most environmentally sound option is steel drive in plus wood post as likely smallest CO2 footprint and both are bio degradable (more or less).