Working with Concrete

Select your question below

What is the right consistency for good quality concrete?

What mix ratio should I use for a path or driveway?

What Personal Protective Equipment (PPE) is required when handling cement based products?

How many bags of pre-mixed Concrete Mix are required to fill a cubic metre?

What does the term MPa mean?

Does the temperature of the air on the day affect the use of concrete products?

How do you cure freshly laid concrete?

What is the difference between cement and concrete?

Why should a shovel not be used to measure concrete or mortar materials?

How quickly will Rapid Set Concrete harden?

What mix ratio should I use for foundations or footings?

What is the procedure for laying a concrete surface?



What is the right consistency for good quality concrete?

Watch this video clip to see the right consistency for concrete

back to top

What mix ratio should I use for a path or driveway?

For concrete made for paths & driveways, mix 1 part Cement Australia Builders Cement with 2 parts sand and 3 parts aggregate.  Approximately 16 x 20kg bags of Builders Cement are required per cubic metre of finished concrete.  

For more mix ratios, check out the Mix Advice section in our Trade Professionals area.

back to top

What Personal Protective Equipment (PPE) is required when handling cement based products?

Always wear the correct protective clothing when handling any product containing cement as it is an alkaline substance in a fine powder form:

  • Gloves - to guard against skin irritation
  • Face mask - to prevent dust inhalation
  • Eye protection - to prevent dust from getting in to eyes
  • Long pants and sleeves - to guard against skin irritation
  • Safety boots - to prevent injuries to your feet when handling heavy items or using potentially hazardous tools

Always separately wash clothes that may be splashed with cement-based products at the end of each day.

back to top

How many bags of pre-mixed Concrete Mix are required to fill a cubic metre?

Approximately 110 x 20kg Concrete Mix bags are required.

back to top

What does the term MPa mean?

MPa is the metric unit for pressure or stress called megapascal (MPa). The term is used in concrete as the common unit for compressive strength. If you have a project which requires a defined strength of concrete - i.e. 20MPa to set the posts for a raised deck - then its time to call in the experts and have concrete delivered from a ready mixed truck – it’s the only way to guarantee the structural strength in the concrete.

You may also see concrete requirements expressed as 'N20/10' - this is where N means normal class concrete, 20 refers to 20MPa of strength and 10 refers to it containing a maximum aggregate size of 10mm.

back to top

Does the temperature of the air on the day affect the use of concrete products?

The ambient temperature can affect the setting times of all types of concrete. If the temperature is less than 10oC, wait until the day becomes warmer and if its over 35oC then postpone the job until it is cooler.

back to top

How do you cure freshly laid concrete?

It is important to moisten the surface and edges of the slab for up to 7 days. This provides a continuous supply of moisture to provide a better surface quality. Curing occurs to ensure that the hardened surface abrasion is developed and dusting is reduced.

Protection should start as soon as the final surface finish is produced and not the next day. 

This can also be achieved by covering the slab with black plastic. Care should be taken to ensure that covering the slab does not mark the freshly poured concrete. Protection of coloured concrete slabs must be considered. If polythene sheets are in direct contact with the concrete variable colour of the surface due to hydration staining may occur and this is not possible to correct at a later stage. 

Alternatively, mist spray the slab at least twice daily for up to 7 days as it is important that the slab does not dry out before the cement has fully hydrated.

 

back to top

What is the difference between cement and concrete?

While the terms cement and concrete are often used interchangeably, it is important to note that cement is actually an ingredient of concrete. Cement is the powder added to concrete that provides the basis for the glue that holds the concrete together. Concrete is a mixture of aggregates (stones) and sand and the paste is water and cement. Through a process called hydration the cement and a portion of the water will undergo a chemical reaction and harden into a rocklike mass.

Contrary to popular belief, concrete “sets” or “hardens” as a result of the chemical reaction between the cement and the water – it doesn’t just dry out.

back to top

Why should a shovel not be used to measure concrete or mortar materials?

Cement is a dry product and is free flowing whereas damp sand tends to clump together. Cement tends to lie flat on the shovel and has less volume than the sand. Using a shovel does not ensure that materials are measured equally and it is recommended that proportions of raw materials are measured with a container such as a bucket.

Always use an accurate measure to add your water too as the most common mistake made when mixing concrete, render or mortar is to add to much water.

Too much water ruins the strength of concrete, mortar and render.

back to top

How quickly will Rapid Set Concrete harden?

Rapid Set Concrete contains cement, sand and aggregate and an additive which causes an initial hardening to happen within 15 minutes of water being added.

In warm temperatures, this hardening is accelerated and can be as fast as 5 minutes!

Never mix Rapid Set Concrete in a vessel like a bucket or a wheelbarrow as it will set hard and ruin it before you can remove the product.  Rapid Set Concrete is designed to be added to clean water in the hole that you wish to fill with concrete.

Watch this video clip to see how to use it to set a post.

back to top

What mix ratio should I use for foundations or footings?

For concrete made for foundations or footings, mix 1 part Cement Australia Builders Cement with 3 parts sand and 3 parts aggregate.  Approximately 13 x 20kg bags of Builders Cement are required per cubic metre of finished concrete.  

For more mix ratios, check out the Mix Advice section in our Trade Professionals area.

back to top

What is the procedure for laying a concrete surface?

This process is referred to as the placing and finishing of the concrete and there are four steps:

  1. Screeding  - which is the initial levelling of the placed concrete using a straight length of wood, aluminium straight edge or a portable power screed for larger jobs.
  2. Bleedwater accumulation  - where the concrete is left for 1 to 2 hours after screeding to allow bleedwater to accumulate on the surface and then to evaporate.
  3. Final floating  - occurs when the bleedwater has evaporated and the top surface is firm to touch and is completed with a wooden or magnesium float.
  4. Final trowelling  - occurs when the concrete surface becomes firm and is often carried out in several passes at intervals of 30 minutes where the concrete receives its final surface finish.

back to top