A review of Metpost fence post supports, their application and whether or not they're any good.
What is a Metpost?
A Metpost is the brand name of the most common metal fence post support. It's a socket that is intended to sit firm to the ground and hold a fence post upright and in place. They're easy to install but the short answer, in my opinion, if they're any good is no. The cost of simplicity is paid for out of longevity and stability. There are however a few small applications where you might get away with them.
The Pros and Cons of a Metpost
Metal fence post supports usually have a metal box that grips roughly the bottom 150mm of the post by means of cut outs in the sides. These cut outs allow for a triangle of metal to be folded inwards and bite in to the post. Fences can receive huge amounts of buffeting from the wind in their lifetime. Wooden posts tend to fail at ground level when surface water rots through the post at that height. Metal post supports are great to overcome this but that only lasts as long as the thin plastic coating on them is intact. After that they become susceptible to rust.
The biggest drawback to a metal post support is that the grip it has on the post just doesn't come close to the strength that the internal fibres of the wood have. Putting a metal post support 600mm in the ground can offer about the same stability as a wooden post in terms of fixing it to the ground if done properly but the difference is the willingness to fold over at ground level. On that front the internal fibres of the wooden post are superior by far.
Another dislike I have for the spike variety of post support is that you just knock them blind in to the ground. Digging a fence post hole allows you to explore the ground as you go down in to it picking up any cables, pipes or other infrastructure that is down there. Most crucially allowing you to avoid it. The metal spike doesn't allow this and if you have a cable underneath where you're about to hammer it in, it's pot luck whether or not you might miss it.
As far as cost goes metal post supports are only a support and you will still need to buy a fence post to go with it. If you buy the bolt on variety that doesn't have the spike and fixes directly to a hard surface you're going to need to get the bolts as well. If you buy the spike variety I'd recommend getting the proper wedge to fit them. It's a block that sits inside the post and protects it as you hammer it in. They usually come with handles on the side to guide them in to place. It is a lot cheaper to buy your wooden post just that little bit longer and put it in the ground with sand and cement (ready made postmix is getting really expensive lately) than it is to buy the post with a metal support.
When to use a Metpost?
Temporary fences. As I said in the opening line the cost of simplicity is paid for out of longevity and stability, if you don't need longevity then there's no problem!
Corners. If a fence post has two panels attached to it at a 90 degree angle so long as the panels are secured propery at the other end that post should stand up with nothing in the ground. There's your stability.
Summary
I'd rather put a 2ft hole in a slab of concrete to get a post in than use a Metpost. That way I go home confident I'm not coming back in 12 months to put a 2ft hole in a slab of concrete! Horses for courses though and that is just a personal opinion.
