Concrete is a mixture of cement, sand, aggregate and water. Combining these ingredients is not hard, but to get the best out of concrete there are a few rules that should be followed. The following guidelines are for concrete mixing amounts suitable for small areas.
Firstly, it is important to properly clear an area. If you are working inside, put down thick plastic sheets. It is also sensible to use an H Class vacuum to prevent concrete dust contaminating the air. The WhaleTale bucket attachment is a great tool for protecting both the user and the surrounding environment. Make sure that container you are using is large enough to contain all the materials you will be mixing.
It is also important that you wear sensible PPE. Cement is caustic and releases heat as it reacts. This results in burns if it is not washed off promptly.
For strong concrete the usual ratio is 1:2:3. One part cement, two parts sand and three parts aggregate. For the majority of application OPC (ordinary portland cement) should be used.
Once you are prepared to mix, slice open cement bag and dump it in the container. Adding water to the cement is where some judgment is needed. Pour a measured amount of water into the cement from a bucket, rather than using a hose. Mix the concrete for a few minutes before adding more water. As the concrete is mixed, it becomes more fluid . Adding too much water early on will cause the mix to become too thin. Keep back a few cups of the dry material in case the mix needs to be thickened.
If the mix is too dry it will appear crumbly, and fall away from the sides of the mixing bucket. Add more water in small doses and mix well before adding any more. If the mix has too much water it will not hold its form. Test this by dragging a trowel through the mix. If it sags back into the trench created, it is too wet. The mix is right if the sides of the container and the ingredients are thoroughly wetted. A trowel patted against the concrete will leave a slightly shiny surface.