Cement, Concrete, Mortar & Masonry Mat Guides

What Cement, Concrete, Mortar & Masonry Materials covers

This section covers cement and the mixes made from it, along with the sands and aggregates that go into them.

The first thing to settle is the vocabulary, because it is the most common counter confusion in the country. Cement is the grey powder — the binder, on its own not a building material. Concrete is cement, sand, stone and water, used where strength and bulk are needed: slabs, foundations, footings. Mortar is cement, sand and water without stone, used to bed bricks and blocks. Screed is a fine mix used to level a floor before a finish goes down. Asking for the wrong one gets you a product that will not do the job.

The second is that sand is not one material. River sand, building sand, plaster sand and silica sand differ in particle size, shape and cleanliness, and they are not interchangeable. Plaster sand is finer and gives a workable plaster; a coarse sand produces a rough, weak plaster. Using the wrong sand is a frequent cause of work that looks acceptable and performs badly.

The third, and the one that costs the most: adding water to make a mix easier to work weakens it permanently. Concrete gains strength from a controlled water-to-cement ratio. Extra water gives an easier mix and a weaker result, and no amount of curing recovers it.

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How the guides in this section differ

Which mix. Concrete, mortar, plaster and screed share ingredients and are not substitutes. The guides say which each product belongs to.

Which sand. Particle size and cleanliness decide suitability. Sand with clay or organic content weakens the mix regardless of how good the cement is.

Which cement. Common cements differ in composition and setting characteristics, and packaging states a strength class. Specialist cements exist for particular conditions.

Structural or not. A garden path and a house foundation are different problems. Anything structural needs designed mix proportions and, generally, an engineer.

Mix	Ingredients	Used for
Concrete	Cement, sand, stone, water	Slabs, foundations, footings, posts
Mortar	Cement, sand, water (often with lime)	Bedding bricks and blocks
Plaster	Cement, plaster sand, water	Coating walls
Screed	Cement, fine sand, water	Levelling floors before a finish
Grout (masonry)	Fluid cement mix	Filling cavities and cores

Safety, accuracy and next-step checks

These guides are informational. Structural concrete work requires professional design and, in most cases, municipal approval under the National Building Regulations.

Points worth carrying:

Wet cement burns. Cement, concrete and mortar are strongly alkaline and cause serious chemical burns after prolonged skin contact — often with little pain until damage is done. Kneeling in wet concrete and letting it enter boots causes severe injuries every year. Wear waterproof gloves and boots, and wash it off immediately.
Cement dust harms eyes and lungs. Wear eye protection and a suitable mask when handling dry cement, and never rub an eye with a dusty hand. Cement in the eye needs immediate irrigation and medical attention.
Cutting and grinding concrete produces silica dust, which causes irreversible lung disease. Cut wet or with extraction, and use a properly rated respirator.
Do not add water for workability. It permanently reduces strength. Use a plasticiser if the mix is hard to work.
Cure properly. Concrete needs to stay damp while it gains strength. Letting a slab dry out fast in South African sun and wind produces surface cracking and a weaker result. Keep it covered and damp for the stated period.
Mind the weather. Very hot conditions accelerate setting and complicate placing; cold slows strength gain.
Use clean water and clean sand. Contaminated sand or water weakens the mix.
Lift correctly. A cement bag is heavy and awkward, and back injuries are the most common site injury of all.

Frequently asked questions

What is the difference between cement and concrete? Cement is the binding powder. Concrete is cement mixed with sand, stone and water. Mortar is the same without stone.

Which sand should I use for plaster? Plaster sand — finer and cleaner than building sand. Coarse or dirty sand gives a rough, weak plaster.

Can I add more water to make it easier to work? No. It permanently weakens the result. Use a plasticiser instead if workability is the problem.

How long before concrete is strong enough? It gains strength over weeks, with much of it in the first days if properly cured. Loading times depend on the mix and the application, and structural work should follow an engineer’s guidance.

Why is my slab cracking? Common causes are drying too quickly, too much water in the mix, inadequate curing, missing reinforcement or movement in the ground beneath. Fine surface crazing differs from structural cracking, which warrants professional assessment.

Cement, Concrete, Mortar & Masonry Materials Used-For Guides