Made by Cement Australia
Concrete · Small jobs and footings
Concrete Mix 20kg
Premix concrete you mix in a barrow or mixer, for small jobs: posts, small footings, pads and garden edges.
Comes on pallets of 48 or 84 × 20kg bags.
1 bag (less than a pallet).
Lead time: Approx. 1 to 2 working days
Code: 200842003
Available to order from Allmat. Click and collect or delivered across Adelaide.
How many bags do I need?
Work it out with the free Allmat concrete calculator.
About Concrete Mix 20kg
Premix concrete: a ready blend of cement, sand and aggregate for small jobs around the home and garden. Add water, mix and place. Cement Australia lists it for footings, small slabs, paths, mower strips, garden edges and pergola posts, and suggests bags for jobs under about 0.1m3: a post, a small footing or a pad.
- Water
- 1.75L per bag
- Yield
- About 110 × 20kg bags per m3
- Coverage
- 2 × 20kg bags: about 450 × 500mm at 75mm thick
- Formwork off
- After 24 hours
- Foot traffic
- After 3 days
- Heavy loads
- After 7 days
Best for
- Small footings and foundations
- Small pads, such as under a tap, bin or air-conditioner
- Mower strips and garden edges
- Posts and pergola uprights
Not for
- Placing below 5°C or above 35°C
- Aluminium posts, unless their maker confirms it suits them
- Jobs that specify a concrete strength such as N20: Cement Australia advises truck-delivered concrete
How to use
- In a mixer, put in 1.75L of clean water per bag first, then tip the mix in slowly. In a barrow, make a hollow in the mix and add 1.75L of water per bag. Mix no more than 2 × 20kg bags at a time.
- Mix it right through. Only if you really need to, add more water about 100ml at a time until it is workable. Too much water ruins concrete.
- Check the mix: it should be neither stiff nor sloppy, and should hold its shape when squeezed in a gloved hand.
- Place it in the formwork, fill the corners and compact it. A non-load-bearing slab should be at least 75mm thick. Level it with a straight edge and finish with a wooden float or steel trowel.
- Keep the surface moist for 7 days for full strength. Formwork can come off after 24 hours. Keep off it for at least 3 days, and keep heavy loads off for 7 days.
- For a post, fill the hole to just below ground and tamp. Leave the bracing on for at least 24 hours and wait 3 days before fixing anything to the post. For a pergola stirrup or a clothesline, allow 7 days before loading it.
The squeeze test, in a gloved hand
Bags or a truck? Cement Australia's volume guide
- Under about 0.1m3: use bags of Concrete Mix.
- From 0.1 to 0.5m3: mix your own with Builders Cement, sand and aggregate.
- Over 0.5m3: ready-mixed concrete by truck, where access allows.
Paths, driveways and slabs are usually a ready-mix truck job.
Storage & safety
Keeps about 6 months from manufacture, sealed, dry and off the ground. Do not use a bag that has gone hard. Wear dust-proof goggles and PVC or rubber gloves. Each 20kg bag is a two-person lift. Storing and handling bagged cement.
- Wet concrete can burn skin, so add a face shield when you work it wet.
How many bags?
Our estimate: about 2 × 20kg bags for a 200 × 600mm post hole with a 90x90 post, on 100mm of gravel with 10% extra.
Not sure this is the right concrete? Compare the four bagged concretes.
Documents
The manufacturer's own sheets. Open one to read it on the page, share it or download the PDF.
Concrete Mix questions
Cement Australia's own FAQs put it at about 110 × 20kg bags of Concrete Mix per cubic metre. A job that size is usually ready-mixed concrete delivered by truck. For a pad or footing, the slab and footing calculators, linked below these questions, work out the bags.
2 × 20kg bags cover a pad about 450 × 500mm at 75mm thick.
Formwork can come off after 24 hours. Stay off it for at least 3 days and keep heavy loads off for 7, keeping the surface moist for those 7 days so it reaches full strength. Drying times for concrete in general are linked below these questions.
A small one, under about 0.1m3, such as the pad drawn under How to use. The volume guide beside that drawing gives Cement Australia's sizes for mixing your own and for ordering a truck.
Linked from these answers: Slab calculator · Footing calculator · Concrete drying time
Sources and guidance
The product information on this page comes from Cement Australia's published product data sheets, safety data sheets and website (see Documents above). It is general guidance only. Other manufacturers may give different advice for their own products, so always follow the instructions on the bag and the product's data sheet. Structural work, such as footings for buildings, must follow your engineer's design and the relevant Australian Standards.
You may also need
Often ordered with this product. Use + Add to pick the option and quantity and put it on the same quote.
PROSTRENGTH Extra Strength Concrete 20kg
High strength concrete mix, designed for up to 50MPa in lab tests. Walk on it after 24 hours.
Rapid Set Concrete 20kg
No-mix concrete for fence posts, clotheslines and letterboxes. Starts to harden within 15 minutes.
Also for this job: Post supports (stirrups)