Check in with concreteshopper’s dozen before your next concrete pour. Before it’s too late.
1. WHAT’S MY SUB BASE LIKE? GROUND SURFACE? DO I NEED CRUSHER DUST OR SOME FILL?
Your sub base needs to be level and free from cracks or imperfections before you commence your concrete slab. Like many sub bases a clay based ground surface expands and contracts with the weather. Hot dry weather may cause your sub base to crack, leading ultimately to cracks within your concrete slab. Crusher dust, manufactured sand or barmac, as it is sometimes referred, makes an ideal sub base. It is easy to level and protects your slab from the cracks and imperfections below. In summer it is still prudent to “hose it down” and wet the crusher dust prior to your concrete pour, otherwise when your concrete is poured it is going to dry, shrink and crack.
2. WHAT SIZE STEEL REINFORCING DO I REQUIRE?
This is a good question, and may well depend on the geotechnical composition of your soil. As a rule of thumb SL62 sheets of mesh are suitable for foot traffic i.e., pathways and patio’s, sheets of SL72 72 are appropriate for light traffic i.e., driveways and garages, whilst sheets of SL82 and SL92 are utilised when heavy traffic and transport is traversing over your concrete slab i.e., in shed slabs or high traffic areas.
3. WHAT STRENGTH CONCRETE DO I REQUIRE? WHAT’S THIS 20MPA, 25MPA MEAN? OR 20/20? 25/10?
The MPA of concrete is a term used to describe the megapascal strength of concrete, or its tensile strength. In layman terms that’s how much stress or pressure it can take before cracks, shears or breaks. 20mpa is weaker than 25mpa concrete, 32mpa and 40mpa concrete and so on. As a rule of thumb 20mph concrete is fine for foot traffic, I.e., footpaths and house slabs, depending on your sub base, whilst 25 mph is more appropriate for driveways and light traffic. 32mpa and 40mpa concrete is suitable for shed slabs and heavy traffic areas. The number after your MPA relates to the size of the aggregate within the concrete mix i.e., 20 for 20 millimetre stone or 10 for 10 millimetre stone. Many concreters find 10mm or smaller stones are easier to place, though in many instances they come at an additional cost.
4. DOES THE CONCRETER I AM HIRING DO THE HAVE TO DO THE JOB HAVE FORMWORK? (I.E. BOARDS?) IF YOU ARE DOING THE CONCRETING YOURSELF, DO YOU HAVE FORMWORK? BOARDS? PEGS?
If the answer to these questions is NO, you may need to consider hiring a concreter or someone who can supply the form work for you. Otherwise form work could be a large expense for you to outlay for a one off concrete job.
5. WHO IS SUPPLYING THE STEEL REINFORCING ACCESSORIES (I.E. MESH AND BAR CHAIRS)? THE CONCRETER OR ME? HOW ARE THEY BEING DELIVERED?
Whether it is you or the concreter supplying it, it is prudent to have someone on site when the steel and accessories are delivered, to ensure everything is there. Make sure the steel and accessories arrive BEFORE the concreter’s arrive, otherwise delays could cost you both additional concreter charges and aggravation.
6. HAVE I ORDERED ENOUGH STEEL, ACCESSORIES AND CONCRETE?
Wow! This is probably THE MOST IMPORTANT thing to consider when organising your concrete pour. Whatever you do don’t under order. Allow for variations and variables in your slab, for not enough steel and accessories can cost another delivery, delays and additional concrete charges. As a rule of thumb when ordering steel remember to divide the square meterage of your site by 12.2 to ascertain how many sheets of mesh you require. When it comes to ordering bar chairs to prop your sheets of mesh up from the ground, remember approximately 18 bar chairs are required for every sheet of 6m x 2.4m mesh. Keep in mind under ordering concrete can hurt your back pocket when you have to order in the 1 cubic metre or less you require, and pay the small load fee that goes with it. That’s if the concrete plant even has a truck nearby to supply it! If not you may even find yourself with a cold joint in your concrete slab. So when you have calculated how much concrete it is you need using our concrete calculator on the home page, don’t forget to add 10% to this figure for safe keeping. It’s better to be sure than short.
7. CAN THE CONCRETE TRUCK ACCESS MY SITE WITH EASE? OR DO I NEED A CONCRETE PUMP? IF SO, DO I NEED A CONCRETE BOOM PUMP, I.E. A PUMP WITH A CRANE, OR IS A LINE PUMP SUFFICIENT I.E. A CONCRETE PUMP WITH RUBBER HOSE?
In situations where the concrete pour is large in terms of quantity a boom pump, though more expensive, is faster, and as such may save you additional man hours on site and thus save you on additional concreter charges. Otherwise line pumps can reach up to 100 metres with their hoses and are capable of avoiding power lines, trees and other on site hazards.
8. WHAT SIZE CONCRETE TRUCKS DO I NEED?
Concrete trucks are usually either six, eight or ten wheelers and carry between 3 and 9 metres. If access is tight at your place you are probably going to need a smaller truck, i.e., a six wheeler. If its too tight a small mimimix truck could be considered if available, or a line pump. Again both these options are at an additional cost. The alternative may be to wheel barrow the concrete in from the street, yet if this is to be considered you may need additional labour. Whilst if it cannot be completed within an hour the concrete plant is going to charge you additional costs for waiting time (e.g., $3 per minute). In situations where you are doing the concreting yourself and do not have enough labour or where a wheelbarrow is required, aim for smaller loads, i.e., 3 or 4 cubic metres, that way you have a better chance of discharging your load and avoid waiting time charges. Check out when waiting time starts with the plant though when ordering. Waiting time may well start earlier depending on your load size. Ask what the plant charges for small loads as well. Some plants charge a small load fee for less than 3 cubic metres of concrete, others charge for small loads less than 4 cubic metres.
9. HOW FAR APART SHOULD I ORDER THE TRUCKS? 20 MINUTES? ONE HOUR?
The timing of your concrete trucks is crucial to a successful concrete pour. When the trucks are too close together concreter feel under pressure and you run the risk of paying waiting time charges, and when they are too far apart you run the risk of concrete going off, cold joints (cracks in the slab) and extra concreter charges as they stand around waiting whilst on hourly hire. Talk with you concreter and/or concrete plant before pouring to ensure the timing of your concrete trucks suits your capabilities on the day.
10. WHAT HAPPENS IF THINGS CHANGE ON THE DAY?
Be prepared, wet weather could delay your concrete pour, your concreter may be ill or caught in traffic, or the concrete pump you ordered may break down. You always need a back up plan. Does the pumper have another pump they can call on? Put in place your fall back position before the day of the concrete pour to hedge against unforeseen circumstances, which could ultimately cost you a small fortune.
11. WHAT’S THE BEST TIME FOR ME TO POUR?
Preparation is the key to a successful concrete pour. Work out when it is most suitable for you to pour and book in early with your concreter and the concrete plant. Concreter’s, concrete plants and concrete pumpers are all busy, and need plenty of notice. Consider the weather conditions on the day of the concrete pour by looking at the Bureau of Meteorology’s (BOM) seven day forecast. Or visit the Cement Concrete and Aggregate Association’s APP to see how concrete conditions are faring in your location. Remember rain, extreme hot conditions, low relative humidity and wind ARE NOT CONDUCIVE to good concreting conditions. Schedule your concrete pour accordingly.
12. WHAT IF THE WEATHER TURNS DURING MY CONCRETE POUR?
Once again be prepared and make provisions for unforeseen weather events. If it’s hot and windy you may need some aliphatic alcohol to provide protection for your slab. If it looks like rain have some tarps or even left over plastic nearby. Maintain solid communication with the concrete plant at all times. They may be able to work in with and either delay or postpone your pour without the need for waiting charges or cancellation fees applying.
Note: Seek the advice of a professional where possible and feel free to email us admin@concreteshopper.com.au .com for further assistance.
