How to Make Concrete Yourself: Proportions and Mixing

A brief guide to making concrete yourself

Concrete is a unique material because it is used not only in construction for erecting buildings, but also for making various items such as balusters, paving slabs, kitchen countertops or even vases. Today, concrete production technologies allow this material to compete with natural materials such as marble or granite. Although the finished product is not as aesthetic as those materials, it does not have a radiation background. If you have decided not to buy ready-made concrete, then in order to make concrete yourself, you must follow certain conditions and production features that determine its quality and suitability. The concrete recipe also changes depending on its application.

To make concrete with your own hands, let us first look at the concept and properties of concrete. Concrete is a mixture of cement mortar with fillers, where the main ingredients are cement, water, sand and various aggregates, such as crushed stone, slag, pebbles, gravel and the like. Special ingredients — plasticizers — may be used as additives, giving the mortar various unique properties.

The main characteristic of concrete is compressive strength, which is measured in megapascals (MPa). Depending on strength, concrete is divided into grades. According to GOST, classes are designated as follows: B7.5 — B80. The differences between them depend on the type of cement used (M300 — M600), the sand, the fraction and the rock type of the crushed stone. The number in the class name shows what pressure the concrete can withstand in most cases. To make strong concrete yourself, you need to clearly determine which concrete should be used. Making concrete yourself will take much more time.

The simplest concrete option is a mixture of coarse sand and ordinary cement mortar. Such concrete is used mainly as a foundation bedding layer, and it is suitable only for protection against foundation settlement and excessive moisture penetration.

Stronger concretes are made by adding different crushed stone fractions of 2–3 mm and 30–35 mm. The quality of such concrete directly depends on the composition and cleanliness of all its components.

How to make concrete at home

The first mandatory component is cement, which binds all the other components together. Usually cement grade 500 is used, and in some cases grade 400 is used, although the strength of the latter is lower. It is better to buy cement immediately before use, because during long storage it loses its qualities. The approximate ratio is as follows:

- more than 1 month — minus 10 percent of strength;

- more than 2 months — minus 20 percent;

- more than 6 months — minus 30–50 percent;

- more than a year — the cement is unsuitable for use.

Cement must be dry and free-flowing. You should not save money by buying damp, unmarked or discounted material, as this may affect safety later.

The second component is sand. Suitable sand for preparation has a fraction from 1.5 to 5 mm, an even size with a variation of no more than 1–2 mm, and must not contain foreign impurities. Such impurities may have a harmful effect on the properties of concrete in the future. According to GOST, sand must meet first-class requirements: this means that various impurities and particles make up no more than one percent, and the filtration coefficient is 5–7 m/day. River and sea sand meet the first class; unlike quarry sand, they do not have such a small fraction and are cleaner.

To check the quality, you can perform a simple test at home. A handful of sand should be poured into a jar of water, shaken and left for about a day. The water above the settled sand should be clean or slightly cloudy. In that case, this sand can be used.

The third component is crushed stone, which should not be replaced with pebbles. Unlike crushed stone, pebbles have a surface that is too smooth and will not bond well with the concrete mortar. Crushed stone is rough and jagged, which promotes reliable adhesion. Only crushed stone with a size from 5 to 35 mm is used. Larger fractions are rarely used in production. Crushed stone should contain as little dust or clay inclusions as possible.

The fourth component is water. Only clean water is used, without oils, silt or chlorine. The amount of water should not exceed 20 percent of the cement mass for the best bonding. If this amount is exceeded, voids will form inside the concrete. When adding water, you can follow a simple rule: if it is suitable for drinking, then it is suitable for concrete.

The fifth component is possible additives, such as plasticizers, various auxiliary components, reinforcing substances or lime. Sometimes lime is added to make surface leveling easier. However, this can damage the normal bond between cement and aggregate, which will affect strength. Plasticizers are used to make the concrete mix more fluid or, on the contrary, more viscous. Their use decreases or increases the required amount of water. Flowable concrete is used when pouring foundations of complex shape: it fills all holes and recesses faster and more reliably. Various auxiliary components are used to give more advanced properties. The properties may differ, such as ensuring setting and hardening of concrete at low temperatures or in the absence of moisture. When concrete is used for a thin screed, reinforcing substances are added — special polypropylene or polyvinyl chloride fiber, which helps prevent situations where the concrete spreads.

Material ratios for preparing concrete at home

Below are tables of ratios for M400 and M500 cement, sand and crushed stone. M400 cement:

M500 cement:

By following the established tables, you can avoid most unpleasant consequences. These are optimal ratios for good density and normal binding ability.

Mixing concrete

Here you need to remember the main rule: you should not mix concrete mortar by hand with shovels. This is very labor-intensive, and any rest or untimely stop in the process will inevitably lead to a decrease in concrete strength. It is unrealistic to mix concrete by hand to meet regulatory requirements.

Therefore, a concrete mixer must be used for mixing concrete. A standard unit with a motor power of 0.5 to 1 kW and a 200-liter drum is quite sufficient. Concrete is mixed as follows:

1. The required amount of water is poured into the drum, except for 10–15 %, which will be added a little later.
2. Cement is added, except for 10–15 %, as with the water.
3. Sand is poured in and mixed for about 2–3 minutes so that all components are distributed evenly.
4. At this stage, all necessary additional components are added.
5. Crushed stone or another aggregate is added.
6. Finally, the remaining water and cement are mixed separately. The resulting cement slurry is added to the drum.

The whole process takes approximately about 10 minutes. Do not overdo it, because if you mix for too long, the cement will begin to set.

Pouring concrete

For proper pouring and distribution of concrete, it must be placed evenly, compacted and checked for the absence of air bubbles in the mix. Vibration is used for these tasks, allowing the concrete to be compacted quickly and efficiently. This can be achieved using special tools. Depending on the work being performed, they are either immersed in the mix or, for screeds, they process the concrete from the surface. At the same time, the surface is leveled and the concrete is compacted. If there is no opportunity to use professional tools and you want to try methods of preparing concrete at home, you can try to do everything manually. A sledgehammer is used for vibration, delivering even blows to the sides of the formwork and to the beams that fasten the form boards.

Also, during concrete pouring, all air must be released from the mix. For this purpose, a sharpened reinforcing bar is used to pierce the concrete to its full depth. When pouring the next layer, the previous layer should be pierced by 10 cm for reliable bonding.

As a result, an even layer should form on the surface, and the concrete should be tightly compacted. Next, the top layer remains to be leveled. This is done in several passes over 2–3 hours.

For drying and protection, the concrete must be covered with film. This will protect it from external factors and will not allow the surface to dry faster than the inner part.

The initial drying time of concrete is about 36 hours. After this period, you do not have to be afraid to step on the layer. Complete drying will take approximately one or two weeks. This depends on the thickness of the layer. After that, further work can be carried out. Concrete reaches maximum strength after approximately one to one and a half years.