Concrete is used on site to make the structural elements of the construction: foundations, slabs, pillars, beams, stairs and floors. It is very important that they are well made and resistant.
What is concrete?
Concrete is a mixture of cement, sand, stone and water that, after a chemical reaction, hardens and turns into a kind of very resistant artificial rock. Concrete can be made on site (mixed or “turned”, as bricklayers often say) or bought already prepared from a concrete mixer truck.
The most important point in making and mixing concrete is that the amount of each of the elements (cement, sand, stone and water) has to be well calculated for concrete to have the right strength.
An engineer and a mason will call this recipe a trace. For example, if too much water is put into the mixture, the strength of concrete decreases. If the mason puts too little water, concrete is then filled with holes. Sticking to the right recipe of the mixture is fundamental for the quality of the concrete!
It is important to note that this recipe varies according to where final concrete is used. For example, concrete used at the base of the foundation takes more sand and stone than that used for beams or floors.
And the trick is that there is no standard recipe to be applied in all cases. This recipe depends on the number of floors of the house, the type of structure that will make, the resistance that it needs to have and the durability that is expected.
So it is important for a professional to calculate the mixture, which will be just right for what you plan to do. A commonly used mixture in most common structures (slabs and beams), which is often used in small projects is the famous “1-2-3”: 1 bag of cement, 30 liters of water, 4 cans (18l) of sand and 5 cans of stone.
Should you prefer concrete to be prepared on site?
You will have to trust the mason because he will mix the amount he thinks is right or follow the engineer’s recipe if there is one available.
In this case it is very difficult to control the quality, which then depends on the dedication and mood of the professional you are working with. At least, make sure that he does not make different recipes for different locations where this concrete will be used.
The mixture should be constant for all places where concrete is used. For example, is the can that is used to measure the ingredients always full?
One option to look at is to rent a hand mixer for the mason. This ensures that the ingredients are mixed better than if they are mixed by hand without any equipment.
The first impression could be that concrete prepared on site is cheaper. This is not always the case. The mason spends a lot of time preparing it. His time is your money.
Should you buy concrete from a concrete mixer truck?
You will have the assurance that the mixture used has the right proportions (it stays with the expected resistance) and saves time on site. People tend to think that it is too expensive and that the concrete mixer truck is only used in large projects (a condominium or a house).
From a price point of view, it is a little more expensive to buy concrete from a concrete mixer truck than to make it on site, but you are sure of the quality of the concrete you receive.
How much concrete is there in a truck? A concrete mixer truck transports an average of 7.5m³ of concrete. Only the foundation of a small house (80 m²) can consume 1 truck. There are companies that sell from 1/4 of the truck load.
Make sure you are ready when a concrete truck arrives
The concrete that comes in a concrete mixer truck is mixed when the truck is still in the company’s distribution center. From the moment water is placed in the mix, it must be poured into the forms of the construction site in up to 2.5 hours.
If this time passes, concrete hardens and will no longer be suitable to be used. So, make sure everything is ready when the truck arrives.
The mason must have already made all required marks and prepared all necessary forms. Shapes and structures must have all frames assembled (structures made of steel bars), well braced and cleaned. When the truck arrives and pours concrete, there is not much that can be done, but let it do the job.
Before hiring a concrete truck, make sure that this vehicle is able to pass through the streets to the house and reach your worksite.
If not, you will waste material (and, of course, your money).