There is a large body of folk knowledge around concrete, some of it sound and some of it expensive. This page takes the two most common shortcuts, poor man's concrete and adding washing up liquid, and says plainly what each one does to the mix.
What Is Poor Man's Concrete?
The phrase is informal, so it covers a few different things. In UK usage it usually means one of:
- A lean mix. Something around 1:3:6 cement to sand to aggregate, or leaner. Far less cement than a structural mix, and correspondingly weaker. This one is entirely legitimate for the right job.
- Soil cement. Existing site soil or crushed material bound with a small percentage of cement. Used properly this is a real engineered technique for haul roads, working platforms and sub-bases.
- Dry pouring. Tipping dry cement and ballast into place and letting ground moisture or rain hydrate it. Common for fence posts, and the version most likely to disappoint.
The first two are genuinely useful. A lean 1:3:6 mix is the correct specification for blinding, mass fill, backfilling and kerb haunching, and paying for a structural mix in those places wastes money. Our mix ratio guide covers where each ratio belongs.
The problem is only when a lean mix is used where a structural one is needed. A slab, a foundation or anything carrying load is not the place. The saving is small, because cement is a modest share of the total job cost, and the failure is expensive because it means breaking out and starting again.
Why Dry Pouring Underperforms
Cement hydration is a chemical reaction that needs a controlled amount of water distributed evenly through the mix. Dry pouring gives up both.
Water arrives from above and from the ground, unevenly, over an uncontrolled period. Some of the cement hydrates fully, some partially, some barely at all. The result has hard zones and weak zones, higher porosity, and considerably lower strength than the same materials properly mixed.
For a fence post in a domestic garden that is often good enough, and people reasonably take the shortcut. It is worth knowing it is a real trade rather than a free one. Our fence post guide covers doing it properly.
The Fairy Liquid Myth
Adding a squirt of washing up liquid to a mix is one of the most persistent bits of site folklore, and it half works, which is exactly why it survives.
What it does: detergent is a surfactant, so it entrains air bubbles. Those bubbles act like tiny ball bearings and make the mix feel more workable without adding water. That is genuinely the same mechanism a commercial air-entraining admixture uses.
Why it is still a bad idea:
- The dose is uncontrolled. Air-entraining admixtures are dosed at around 0.02 to 0.1 percent of cement weight, a tiny and carefully measured quantity, targeting 4 to 6 percent air. A squirt from a bottle is a guess.
- Air costs strength. Compressive strength drops by roughly 5 percent for every additional 1 percent of entrained air. Controlled, that trade buys freeze-thaw durability and is worth it. Uncontrolled, you are simply losing strength.
- Detergent is not an admixture. Washing up liquid is formulated to cut grease, not to work in a cement matrix. The surfactant can interfere with hydration, and the bubble structure it creates is coarser and less stable than the fine, closely spaced voids a real air-entrainer produces, which is what actually delivers freeze-thaw protection.
If the mix is too stiff to place, the correct answer is a plasticiser at the manufacturer's rate, which improves workability without the water and without the guesswork. Our admixture dosage guide gives the rates, and the admixtures guide covers what each type does.
Shortcuts That Do Work
Not all folk knowledge is wrong. These are sound:
- A lean mix for non-structural work. Correct specification, not a compromise.
- Fibres instead of mesh in many ground-bearing domestic slabs, which removes the labour of laying and tying steel. See fibre versus steel mesh.
- Covering a fresh pour with polythene to retain moisture. Costs almost nothing and materially improves the finished strength.
- Spending the budget on the sub-base rather than a higher grade. Consistently the better value, as covered in can you pour concrete onto soil.
The pattern is that the shortcuts which work reduce labour or improve curing, while the ones that fail try to cheat the chemistry. Cement hydration does not negotiate.
If a job has moved past what is sensible to mix by hand, our concrete calculator will give you the volume, and volumetric supply means no full-load minimum on a small pour.
What does Coca-Cola do for concrete?
The phosphoric and carbonic acid in cola will very slowly etch cured cement paste, which is why it appears in tips about cleaning cement residue off tools. It is far weaker and slower than a proper acid-based cement remover, and poured into a fresh mix it simply adds sugar, which is a powerful retarder that can delay set badly or prevent proper hardening. It is not a useful admixture.
