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Tips for mixing and casting concrete slabs

Pouring a concrete slab

Casting a flat concrete slab may seem like an easy task, but there are some important details to remember that will make process safe and successful. One of the first things that contractors will learn on the job is how to pour a flat slab of concrete, whether it is for a floor, countertop or a base for an object.

Here are some things to consider before, during and after pouring concrete slabs. These tips will ensure that you don’t waste money or time during the process. Once you have built the wooden formwork and mixed the batch of concrete, remember the following points:

Safety is paramount

All contractors should wear appropriate safety gear when working with cement and concrete. Workers should have dust masks, goggles, gloves, boots and overalls. Appoint one employee to perform a quality check of the building materials and equipment before mixing the concrete. 

This will ensure that everything is in working order and that a high-quality batch of concrete is created. It will also ensure the safety of other contractors as faulty equipment, such as cement mixers, could lead to injury. This designated worker can also file safety reports and create quality checklists if needed.

Create a detailed batch report system

Before mixing the concrete, print out a detailed batch report that lists all the building materials needed and their quantities for each batch. When measuring out the sand, gravel, cement and water, put a tick beside each material. When adding the materials to the mixer, put another tick next to each item on the list.

This double-tick system will help you keep a detailed record of your building materials and see if there are any discrepancies or losses. It will also help you to accurately calculate how much concrete you will need to mix for the slabs. The batch report can be used for future reference so that you can easily recreate the slab with the correct quantities of materials.

Keep materials, tools and equipment nearby

It will help you to keep all of your building materials (sand, gravel, cement and water) near to the location where you will pour the concrete slabs. Also have all the necessary tools and equipment nearby. This will save time and effort when you need to quickly add some more materials to the concrete batch. It also makes it easier to carry heavy bags of cement or wheelbarrows of sand if they are stored close to the working site.

Pour multiple slabs from the same batch of concrete

If you are pouring several slabs at once, it is important to mix a large batch of concrete and use it to pour all the slabs, rather than mixing a small batch for each individual slab. This will ensure quality and consistency between all the slabs. Any variation in the ratios of wet and dry ingredients will easily be seen in the slabs. By mixing one batch of concrete, you will end up with identical slabs. 

Add materials to the mixer in the correct order

There is actually an ideal order in which building materials should be added to a cement mixer; sand and gravel go in first, followed by water and any admixtures. Next add any fibres and pozzolans. Lastly, the cement should be added gradually to the mixer.

The reason for following this order is simple; if you add cement first, followed by water, it can clump inside the mixer. Mixing the sand and gravel with water first ensures that all of the aggregates are wetted and dispersed. When the cement goes in last, it will combine nicely with the other materials to form a high-quality batch of concrete.

Some other points to remember

If you are hand-packing a stiff batch of concrete into a wooden form, make sure that the concrete goes into every edge and corner of the mould. If you are pouring a fluid mix of concrete, make sure that you release all the trapped air bubbles by tapping on the side of the formwork. 

If you are using steel rebar for reinforcing, make sure that it is suspended in the middle of the concrete batch and that no rebar stick out of the surface of the slab. These are some of the points to remember when pouring concrete slabs. Some of these details can be overlooked, which could affect the quality of the slab, so keep these tips in mind.


LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges. 


LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in Mbeya, Southwest Tanzania.


At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.


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