When garden talk turns to retaining walls, it tends to be all about durability, and rightly so, because there is not just longevity at stake here, there’s safety too. That is why Standards Australia have an interest in the subject, with its own standard, AS4678, to be precise.
When we look at the best post for a retaining wall, then, and the straight choice between steel and concrete, the basic requirement is that whichever you go for satisfies AS4678. If it doesn’t, there is no conversation. But either can pass the test, as long as they are of sufficient size and strength.
That reduces the number of factors involved in your choice to two: appearance and cost. If you think that durability, weight and ease of installation should be on the list, you’re right, but those considerations show themselves in the cost column. Let’s deal with that side of it first.
What is the Best Post for a Retaining Wall?
That’s a different framing of the same question, and it has to be answered, so here goes. Steel posts are cheaper in themselves than concrete ones. If initial cost was the sole consideration, you could go right ahead and order them now. But there is also maintenance to think about. Steel, as great a material as it is, comes with an inescapable downside: it is vulnerable to rusting. It can be protected by galvanising, but that is not investing it with a superpower. Many people don’t realise that galvanisation doesn’t alter the basic composition of a metal.
You look at galvanised roofs and fencing a few years down the line, and what do you see? Rust. That’s because to galvanise steel is to give it a coating of zinc, which will do a great job for several years as long as it isn’t scratched or scraped off. So, it’s a bit like you wearing a suit to do the gardening: fine as long as you take it easy and you’re careful not to damage it, but ultimately you can’t guarantee that, not if you’re going to do the job properly. The posts that support your retaining wall will be out there in all weathers for years on end, while you or whoever else gets the work done around them. They need to be virtually indestructible.
What is the Most Attractive Material for Retaining Wall Posts?
Is this a serious question? Sadly, it does get asked from time to time, but it’s like being determined to buy a yellow car just because it’s bright and beautiful, regardless of the make, its reputation and its performance. Fair enough, given that you’ve determined that concrete posts and a concrete sleeper-based retaining wall are the way forward in practical terms, the issue of aesthetics may raise its head. Can concrete be attractive in the same way that wood is? Can steel posts look sexy, come to that?
Concrete is not the glamour material of the building world, but it has smartened up its act in recent years. With modern techniques, you can have a textured effect that is modelled on wood, if that is what really floats your boat. Different colours, too. Look at Aussie concrete experts Realcrete’s product list, for instance, and you will see neat piles of attractive materials with names like stack stone quartz, smooth face lava, bluestone, sandstone, quartz and weathered grey. Yes, weathered. There is nothing wrong with grey if it has a bit of character. But of course, the decision is yours. Just be aware there are more options in concrete than many people imagine.
What is the Best Material for a Retaining Wall?
This question will probably have been answered before you get to the posts. Answered to your satisfaction, anyway, because “best” is a matter of opinion. What is the strongest type of retaining wall is another one, although “strongest” is a term for which there is only one answer. That answer is, the strongest retaining wall is based on the biggest and best concrete railway sleepers. Railway-type sleepers, that is, because the boom in building railways is long gone and the sleepers we use as immovable objects in a garden are products of railway technology, which developed beyond the tradition of using wood to the stern, unyielding character of concrete. It doesn’t rot, it doesn’t split, and it doesn’t get eaten by termites. Concrete sits there and does its job, which is basically nothing, just being tough.
If concrete is the best material for a retaining wall, who would you use anything else for the posts that form such an important part of the barrier – and a retaining wall is just that: a barrier that keeps a heavy mass of soil in place. Why would you use wooden posts? You wouldn’t.
Why would you use steel posts? Because they are lighter than concrete ones and easier to work with, perhaps. But as we have already seen, maintenance is going to add to the overall cost, and if the posts break down before the wall does – even if that is 20 years down the line – you’ve got more expense replacing them. A chain is only as strong as its weakest link, so why install a link that you know is weaker than the rest? It doesn’t make sense.
There is an argument that concrete posts are in fact less durable than steel ones, and this kind of thing is hard to prove one way or the other. It is not the sort of research scientists concern themselves with too much and the only real evidence is gleaned by the gardeners and engineers who are called in to fix such walls when they have begun to fail.
However, if you have already come down on the side of concrete sleepers as the basis for all things heavy and durable in the garden, it is logical to use reinforced concrete posts too. Okay, they are heavy and take a bit of installing, but you as the customer are not going to be troubled by that. You will be trusting a company with the skilled staff and powerful heavy machinery, and this is all in a day’s work to them. If you had the house built from scratch, you didn’t agonise over the foundations; concrete is accepted as the ideal material for this kind of grunt work.
How Deep Do Steel Retaining Wall Posts Need to Be?
If you are still debating steel vs concrete, here’s another thing to consider. Both steel and concrete posts for retaining walls need to be buried way down, probably as deep as the wall is high. This will depend to an extent on the type of soil you are dealing with, as some provide more stability than others. Again, here you will put your trust in the professionals who are doing the work for you.
All in all, the answer to all your questions regarding retaining walls and their posts is to choose your contractor carefully. Ideally use a firm that has great experience in your local conditions and has handled jobs as big as yours or even bigger. Check them out, including the gallery on their website and remember that while good reviews may be suspiciously glowing, bad ones can be unreliable too. Statistically, complaints are more common than words of appreciation, so be careful what you believe – and word of mouth is a great thing when people are talking about quality and performance, but when it comes to appearance it’s all a matter of personal taste.
So, get your retaining wall built to last for ages and you can make sure it’s attractive too.
