What is the difference between cement, concrete and mortar?
Cement is an ingredient, not a material. What you actually make with it — mortar, concrete or screed — and why asking for the wrong one gets you the wrong thing.
- Difficulty
- beginner
- Time
- 8 min
- Read
- 3 min
Short answer
Cement is the grey powder that binds the others together and is never used alone. Mortar is cement, soft sand and water, for bedding and jointing brick and block. Concrete is cement, sharp sand, coarse stone and water, for carrying load. Screed is cement and sharp sand with no stone, for levelling a floor over something else.
This is the single most common misunderstanding in DIY building, and it costs people a wasted trip. Someone lays a shed base with "cement" and finds they have bought a bag of powder; someone else beds bricks in concrete and cannot get a joint to look like anything. The diagram sets it out: one ingredient, three recipes.
Step by step
- Understand cement as the binder.Portland cement is a fine grey powder made by firing limestone and clay. Add water and it reacts chemically and hardens — it does not dry, it cures. On its own it is brittle and expensive and shrinks badly, so it is always mixed with sand or stone that does the bulk of the work.
- Understand mortar as the bedding and jointing material.Cement plus soft building sand plus water, often with lime or a plasticiser. The fine sand makes it buttery, so it spreads under a brick and stays where you put it in a joint. It is deliberately weaker than the brick it beds.
- Understand concrete as the load-carrying material.Cement plus sharp sand plus coarse aggregate up to about 20mm plus water. The stone is what makes it strong in compression. It is far too coarse to lay a brick on and far too strong to point with.
- Understand screed as a levelling layer.Cement plus sharp sand and water, with no coarse aggregate, laid over an existing slab to give a flat floor surface. It is not a structural material — it relies on the slab underneath it and it will crack if it is used as one.
- Know what to ask for at the merchant.A bag marked "cement" contains cement only. A bag marked "concrete mix", "mortar mix" or "postcrete" is already blended and needs only water. Ballast is sand and stone already mixed, so you add cement and water to it to get concrete.
- Do not substitute one for the other.Concrete used as mortar gives joints that will not tool and bricks that will not bed. Mortar used as concrete has no stone in it, so it is weak, shrinks and cracks. Cement used alone as a repair filler shrinks off whatever you put it on.
Tips
- Everything in this family cures rather than dries. Keeping it damp makes it stronger; letting it dry out fast makes it weaker.
- "Cement" is used loosely in speech to mean concrete. If somebody is telling you about a cement driveway, they mean a concrete one.
- Mortar for laying and mortar for pointing are the same material, just mixed to different consistencies for the two jobs.
Common mistakes
- Buying cement when the job needs concrete — Cement alone will not make anything. You also need ballast, or separate sharp sand and aggregate, and the ratio between them is what determines the strength.
- Assuming stronger is better — Mortar has to be weaker than the brick or block it beds so that movement and moisture are taken by the joint rather than by the masonry face. A stronger mix is actively worse.
Questions people ask
Can I make concrete just by adding stones to mortar?
Not usefully. Mortar uses fine, slightly clayey building sand, which is the wrong aggregate for concrete and gives a weaker, more shrinkage-prone result. Use sharp sand and graded aggregate, or all-in ballast.
Is cement the same as Portland cement?
In everyday use, yes. Nearly all general-purpose cement sold in the UK is Portland-based, though bags carry a code describing exactly what has been blended into it.
What is mortar with lime in it for?
Lime makes a mortar more workable, more forgiving of movement and more breathable. It is essential on older solid-walled buildings and useful on modern work.