Is Postcrete as strong as mixed concrete?

The comparison people make is the wrong one. Post mix is not competing with concrete on ultimate strength — a fence post is not a highly loaded thing and both materials are comfortably strong enough. It is competing on labour, on time, and on how much of a Saturday you would like to spend mixing.

Step by step

1. Use post mix where speed and simplicity are the point.A few posts, a single replacement, working alone, no mixer, no water on site beyond a can. The saving in effort is enormous and the cost difference over a handful of posts is small.
2. Use mixed concrete for a long run.A whole fence line, a set of gate posts and a run of intermediate posts. Once you are past a handful of holes the price gap dominates, and if you are hiring a mixer anyway the marginal cost of another hole is almost nothing.
3. Follow the water-first instruction.Most fast-setting post mixes want the hole part-filled with water and the powder poured in afterwards, not the other way round. Getting this backwards is the commonest reason for a soft or uneven set.
4. Brace the post before adding anything.Post mix gives you a couple of minutes and no more. Have the post plumbed and braced in both directions before the bag is opened, because there is no adjusting it afterwards.
5. Never use post mix for a slab or a footing.It is designed for a confined hole with a post in it. You cannot place, compact, screed and finish something that sets in minutes, and it is not batched or specified for structural concrete.
6. Slope the top away from the post.Whatever you set it in, the top surface must fall away from the timber so that water runs off rather than sitting against it. A flat or dished top around a timber post is what rots it at ground level.
7. Consider drainage under the post.A post set in a sealed concrete cup stands in whatever water gets in. Gravel in the base of the hole lets that water away, and it makes a substantial difference to how long a timber post lasts.
8. Give gates and heavy posts more than the standard treatment.A gate post takes a large and constantly changing load. It wants a deeper, wider hole and more concrete than a fence post, and it should be left much longer before the gate is hung on it.

Alternatives

• Fast-setting post mix (Postcrete and equivalents): Poured dry into the hole with water added, no mixing. Goes off in minutes, holds a post within about a quarter of an hour, and takes load the same day. Expensive per hole. Ideal for a handful of posts, a repair, or working alone with no mixer.
• Hand-mixed or mixer concrete: Far cheaper per hole, and once you are setting more than a few posts the cost gap becomes the deciding factor. Needs bracing to hold each post while it sets, and the posts cannot be loaded for a day or more.
• Metal post spikes or bolt-down shoes: No concrete at all. Quick, reversible, and fine for a light fence in firm ground. Considerably less rigid than concrete and prone to working loose in soft or wet ground or on an exposed windy boundary.
• Compacted gravel or a dry mix: Post set in well-compacted angular gravel, or a semi-dry sand and cement that takes moisture from the ground. Both drain freely, which extends the life of a timber post considerably compared with a post sitting in a concrete cup.

Questions people ask