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Cement and concrete are the foundation of many D.I.Y. projects. There are many different kinds of cement products available, so it can be tricky to work out which one you need.
Here’s how to choose the right ones so that you get a fantastic result every time.
The difference between cement and concrete
Cement and concrete are different things. Cement is a mix of mineral materials that have been heated, ground and blended to create a very fine powder. Cement powder reacts with water to set hard, but cement is never used on its own because it is brittle when set.
Concrete is a blend of cement and other materials, such as sand and gravel. It's much stronger than cement on its own.
Cement-like products date all the way back to ancient Egypt. Many ancient Roman structures built using concrete still survive today.
Ingredients of cement-based products
Quick-set concrete is suitable for non-structural uses
Cement is only one ingredient in your cement-based products. Here’s a look at the different products as both individual ingredients and mixes.
Cement
This is the powdered ingredient. It’s generally a grey powder but there are white, off-white and ivory cements available for when lighter colours are required.
Sand
Sands are added to cement to achieve different outcomes.
Sand with a clay component, often called “brickies’ sand”, is used in mortar and render to make it more sticky and workable.
Clean, washed beach or river sand is used in sand-and-cement blends for a strong product with a smooth finish. Sand adds bulk to the mix, as well as a degree of strength.
Gravel
Often referred to “aggregate”, gravel adds compressive strength and bulk to concrete. The most common is “blue metal”, a crushed basalt.
River pebbles, quartz and other aggregates can also be used for a decorative finish. Recycled aggregates are also available.
Concrete
Used for structural or supporting situations, concrete is a blend of cement, sand and aggregate. It will often be used in conjunction with reinforcing steel to increase overall strength.
Sand and cement
A blend of sand and cement is used for non-structural situations, such as garden edging and for setting around pipes in brickwork.
Mortar is made to be pliable and stickyMortar
Mortar is a blend of sand and cement, with hydrated lime (calcium hydroxide) added to make it sticky and more workable. It’s used for bedding and joining bricks and blocks in walls and other structures.
Render
Render mixes are similar to mortar but usually include more fine clay to further increase plasticity. Render is used for coating indoor and outdoor brickwork and block work to achieve a consistent finish.
Quick-set products
Usually only available as bagged products, these include additives to accelerate curing. They are designed for situations where rapid setting is required. Many have a lower strength rating than regular products.
How to understand concrete strength
The compressive strength of concrete is measured in MPa (megapascals). This indicates how much weight the concrete can bear without cracking.
Low-MPa concrete will crack under a lighter load than a high-Mpa concrete.
The strength of a concrete depends on the ratio of the ingredients.
For example, take a dry mix that includes 20kg of cement. If you add 10L of water you will have a strong 35MPa mix. If you add 15L of water you will have general-purpose 20MPa mix. If you add 20L of water you will have a nearly unusable 10MPa mix.
Bagged cement products have the required volume of water listed on the bag, so make sure you only add the correct amount. It is important that you only use clean, clear water for adding to your mixes, whether they be bagged pre-mix or a D.I.Y. bulk blend.
High-MPa pool concrete is pumped and sprayed onUses of different strength mixes
Below 20MPa: Regular quick-set products for filling or anchoring jobs that don’t require structural strength. Such as letterboxes, fence posts, non-structural retaining wall posts and clotheslines.
20 to 25MPa: Typical concrete mixes for house and shed slabs, home driveway slabs, pathways and reinforced footings and foundations.
30+MPa: High-strength concrete for multi-storey house slabs and footings, driveways that carry trucks, and footings for tall retaining walls.
Swimming pools are most often formed using shotcrete, a specially blended concrete that is sprayed into place. This is generally rated between 30MPa and 50MPa.
How to mix your own concrete
For most D.I.Y. projects you can’t beat the convenience of a bagged, pre-mixed product. Sometimes, however, you might want to blend your own mix in a wheelbarrow or a mixer on site.
When creating D.I.Y. blends always mix the dry ingredients to a consistent blend before adding water. Add a little water at a time until you reach a consistency that is suitable for your needs.
Concrete should be smooth and just pourable. Mortar and render should still be a little clumpy.
Here are some examples of mixing ratios:
Render is formulated to stick to vertical surfacesConcrete
High-strength and watertight – 1 part cement : 1.5 parts sand : 3 parts gravel
General purpose – 1 part cement : 2 parts sand : 3 parts gravel
Foundations and footings – 1 part cement : 3 parts sand : 3 parts gravel.
Sand and cement
1 part cement : 3 parts sand.
Mortar
General purpose – 1 part cement : 4 parts sand (brickies’ sand is often used)
More plastic/workable mix – 1 part cement : 6 parts sand or brickies’ sand : 1 part hydrated lime.
Render
1 part cement : 3 parts sand : additives to suit
Some situations call for adding 1 part hydrated lime (note that lime should not be included when rendering below a damp course).
Renderer’s clay or admixes may also be added.
How to use different cement products
It's important to use the right product for the job. Here's a basic guide:
- Concrete – Paths, driveways, large and small slabs, footings and foundations (mostly in conjunction with steel reinforcing)
- Quick-set concrete – Fence posts, letterboxes, clotheslines, non-load bearing retaining walls or pergola posts
- Quick-set high-MPa concrete – Load-bearing situations such as large retaining walls, footings or gate posts
- Sand and cement – Patching around pipes in concrete or brickwork, shower bases, garden edging, bedding toilet pans, moulded products, fish ponds
- Mortar – Laying bricks and blocks, securing paving edges
- Render – Finishing brick and block walls, interior and exterior.
Oxides can be added to colour cement productsAdditives for cement products
There are many additives that can be used for different purposes.
- Hydrated lime – Used to make mixes more workable and sticky
- Oxides – Allow you to change the colour of mixes. Most often used with white or off-white cements to maximise colour
- Renderer’s or builder’s clay – Used in mortar or render to increase stickiness and plasticity
- Admixes – A broad range of products that can do things like making material more workable and making mixes waterproof
- White brickie’s sand – Most often used in mortar or render with white or off-white cement.
Cement and concrete safety
Cement products pose a range of health and safety hazards. To stay safe while using them remember:
- Always follow safe lifting procedures when moving cement bags.
- Always wear suitable personal protective equipment, such as eye protection, a respirator and leather gloves. Dry cement product is both abrasive and alkaline. As it is a fine powder it becomes airborne very easily and can get into the eyes, nose and lungs, where it can be very damaging in both the short term and long term. It can also cause skin reactions and burning.
- Wet cement-based products are hazardous to skin and eyes. They are very caustic and can cause chemical burns.
- Cement-based products generate heat as they cure. In large pours this heat can cause serious burns with extended physical contact.
How to clean up cement and concrete
Cement products will stick to just about anything as they cure. This can result in tools becoming clogged up with material. Remember to:
- Wear PPE, mainly eye protection and gloves, when cleaning up.
- Thoroughly hose down all tools, including wheelbarrows and mixers, even if they will only be left standing for a short period. A mixer can be left running part-filled with water to prevent cement products setting.
- Use a stiff scrubbing brush to remove residue from tricky spots on wheelbarrows and mixing tools.
- Don’t wash cement products down gutters or drains as they can cause blockages and pollute waterways. Wash them out on the lawn and rotate to different spots to avoid damaging the soil.
If you’re planning projects at your place you’ll find it’s worth taking the time to get to know cement products. Once you do you’ll understand how useful and versatile they are and how, when used well, they can take your D.I.Y. projects to the next level.
More helpful tools and materials tips
The Bunnings Workshop community has also shared these useful guides as part of our How To series:
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