The Secret of Strong Concrete
Making concrete is easy. There are many small concrete projects that you as a homeowner can confidently tackle using PPC SUREBUILD Cement 42,5 N with extra strength. Foundations, flooring slabs, fish ponds and driveways are just some reasons to learn how to mix concrete. By doing these projects yourself you can save money.
When learning how to make concrete, remember that the secret to strong concrete is to use a power-packed cement like PPC SUREBUILD Cement 42,5 N with extra strength, and never too much water. PPC SUREBUILD Cement 42,5 N with extra strength makes more concrete than regular class 32,5 general purpose cements.*
*For more details on comparative mixes, see the Affordable Housing page.
What Materials Do I Need?
- PPC SUREBUILD Cement 42,5 N is ideal for making concrete, mortar and plaster. PPC SUREBUILD Cement 42,5 N complies with SANS 50197-1.
- Clean Concrete Sand - ask your supplier for clean concrete sand. The sand should be free of twigs, roots or other foreign matter.
|3. Clean Stone 13 mm to 19 mm in diameter is the ideal stone size.
4. Clean Water - if you can drink it, it is suitable for making concrete. Add sufficient water to obtain a workable, plastic mix. Too much water will weaken the concrete.
PPC SUREBUILD Cement 42,5 N Concrete Mixes
How Much Concrete Will I Need?
Concrete is always poured into a ‘form’ or hollow in the ground. To work out how much concrete you need you first need to measure the volume of the space you are going to fill.
|1. Flat Slabs/ Foundations/driveways
Using a measuring tape, measure the length, width and depth of the area to be filled and multiply these together to work out how many cubic meters (m3) of concrete you need, e.g. length 4,5m, width 4m, depth 0,1m = 1,8m3.
2. Post Holes (Cylindrical Forms)
When making concrete for post holes, use a measuring tape to measure the diameter (width) and depth of the hole. Now multiply the diameter by the diameter and multiply this total by the depth and then by 0,8 to work out how many cubic meters (m3) of concrete is needed, e.g. Diameter 0,3m, Diameter 0,3m, Depth 0,5m (0,3 x 0,3 x 0,5 x 0,8 = 0.036m3).
How Much Material Should I Order?
See details on the back of the PPC SUREBUILD Cement 42,5 N with extra strength bag or refer to the PPC Cement, 'The Sure Way to Estimate Quantities' leaflet to calculate the amount of PPC SUREBUILD Cement 42,5 N, sand and sstone you will need.
As a rough guide, to mix 1 cubic metre of concrete (1m3) you will need 4.6 bags of PPC SUREBUILD (depending on the strength of the concrete required) plus approximately 0,61m3 of sand and 0,76m3 of stone.
How to Mix Concrete
1. Concrete Mixer
If you use a concrete mixer the batch size should suit the mixer. Underfilling the mixer wastes time, while overfilling results in spillage and poor mixing.
a. Measure the quantity of stone and place in the mixer. Add a little water to wet the stone
b. Add the measured quantity of PPC SUREBUILD Cement 42,5 N
c. Add the measured quantity of sand d. Finally add water, a little at a time, until the concrete is flow able but not runny
2. Manual Mixing
For small batches: mix in a wheelbarrow.
For larger batches:
a. Measure out the sand and place in a long, thin heap on a flat, clean, hard surface
b. Pour out PPC SUREBUILD Cement 42,5 N on top of the sand
c. Mix the cement, sand and water thoroughly, leave adding the stone to last - this saves a lot of effort. The cement, sand and water mixture, once mixed thoroughly, will look runny but will stiffen as soon as the stone is added. Ensure the stone is mixed throughout the concrete before transporting the concrete
WARNING: Too much water will reduce the final strength of your concrete.
How Do I Place Concrete?
Once you’ve mastered how to mix concrete, and how to make concrete, you’ll need to successfully place it. This is a technique that ensures best practice for the long-term durability of your project:
- Concrete must be placed within an hour of mixing.
- Place the concrete as close to its final position as possible.
- If the concrete is being placed on the ground, make sure the ground is dampened with a spray of water before placing concrete.
- Once placed, spread the concrete evenly with a rake or spade.
- The concrete should be well compacted or ‘tamped down’ with a rod or spade, making sure that the concrete fills the form or hole completely.
- To create flat surfaces use a wooden straight edge tool. First use a ‘chopping’ motion, then a sawing motion to flatten the surface and then strike off the excess concrete.
- Concrete slabs or driveways should be divided into panels to limit cracking. Joints should be no more than 2,5metres apart for 80mm thick slabs and 3,0 metres apart for 100mm thick slabs.
- Once the concrete has stiffened, keep it concrete damp by covering it with plastic sheeting, damp hessian, damp sand, or by spraying it with water regularly. For optimum strength, this curing process should be continued for 7 days.
- For driveways, keep vehicles off concrete for at least 7 days.
Tips for Using Concrete in an Environmentally Responsible Manner:
- Use the recommended mix design proportions on the bag to mix the concrete
- Use the correct strength mix to minimise waste
- Do not add too much water – this will reduce the concrete strength
- Mix just enough concrete (mortar or plaster) for your project
- If you are building a house, make sure you design for optimal energy efficiency
- Use good quality aggregates and potable water
- Cure the concrete properly to get maximum durability
- Do not waste water when cleaning
- Dispose of your paper bags in a responsible manner
Use local raw materials - this reduces the carbon footprint of the transport component
- Recycle building rubble where possible
For more advice on how to make concrete, ask your PPC Cement stockist or call the PPC toll-free help line: 0800 CEMENT (236 368) - SA only.
Click here for this information in downloadable PDF format.