Oct 2018 METHODS OF CONCRETE MIXING
Concrete, the most extensively used material in construction, DIY projects, home improvements and renovations; Sephaku Cement explains the ideal methodology on how to mix concrete. With the objective to maintain quality and durability of the end result, concrete mixes can be made up of various additions that influence the overall strength and wet mix properties e.g. workability, compact ability, finish ability. At its core concrete is made up of Portland cement, sand, stone and other aggregates mixed together with water and the necessary chemical admixtures. When mixed with different aggregates, concrete mixes can produce a variety of results.
- Mortar mixes -Cement mixed with sharp sand less than 4mm in diameter cement mortar results in a strong and sticky plaster ideally used to glue bricks and cladding in place. The perfect mix will see a consistency that is workable but not sloppy and will not slouch when applied.
- Plaster mixes – used for smoothing over bricks to create a polished and consistent finish, plaster projects result in the best finishes by making use of river sand that is free from dust, mud and organic materials larger stones and wood chips.
- Concrete mixes – by using a combination of aggregate for added strength and load bearing durability, mixed to a smooth and plastic consistence; cement for concrete sees a mix of Portland cement, with sand and stone or coarse aggregate / gravel, admixtures and water.
Well mixed concrete forms the basis of a variety of construction and building uses where strength and durability should not be compromised. When assessing the ideal concrete mix, making sure that it has been blended well the perfect concrete mix should take on the following characteristics;
- The mixture including the incorporation of aggregates, sand and admixtures of both coarse and fine materials should be uniform and consistent. Pay close attention to the colour of the mixture as this will also indicate whether the mix has been properly combined.
- Ensure that the cement and water paste is pulled through to all of the aggregate and that the segregation of any portion in the mix does not occur.
- A concrete mix that is too wet will appear sloppy and will result in weak concrete once cured.
- A concrete mix that does not have enough water added to the mix will be crumbly and unworkable.
- Check the slump of the concrete mix by pouring some into a plastic cup. Tip the cup out as if you were building a sand castle. The ideal mix will slump to about half the height of the plastic cup. Too wet and the mix will slump much lower and will tend to segregate , too dry, the “castle” will stand tall.
To Follow See Steps and Top Tips To Mixing Cement
Step 1: Mix the dry ingredients made up of one part cement to two parts sand and four parts stone gravel / course aggregate. Premix concrete options are also available which have the required qualities of sand and aggregate already mixed together.
Tip – Begin with a moderate volume of mix, the greater the quantity the more difficult it is to mix especially by hand.
Step 2: Combine the dry ingredients with wet by slowly adding water, little by little. By doing so slowly makes the (hand) mixing process much easier and ensures that not too much water is added in error.
Tip: When making use of ready mix concrete in bags follow the mixing instructions by measuring out the prescribed amount of water first.
Step 3: Mix the concrete ensuring that all ingredients are combined together and adequately blended with the water. The consistency should be uniform and with a medium slump
Tip: If available make use of an electric concrete mixer, this will not only ensure that the mix is properly combined but will require less manual effort when hand mixing concrete.
Step 4: Pour your concrete mix at the point where it can be compacted the less you have to move the concrete after placing the better and let it cure. Cover with plastic to ensure that moisture does not evaporate too quickly especially under warmer conditions.
Tip: If you need longer setting times contact a reliable chemical admixture company for product and instructions on how to use the retarders. Only small amounts of admixture are sometimes needed to extend setting time by 1 to 4 hours.