How to Make Concrete Yourself: Proportions and Mixing

A brief guide to making concrete yourself

Concrete is used not only in construction for buildings, but also for making different items: balusters, paving slabs, kitchen countertops and even vases. Modern concrete technology allows it to compete with natural stone, such as marble or granite, in some applications. If you decide not to buy a ready-mix product and want to make concrete yourself, it is important to choose the right proportions of cement, sand, crushed stone and water: strength and suitability depend on the mix composition, aggregate quality, water-cement ratio and curing after placement.

To make concrete yourself, it is useful to understand its composition. Concrete is a mixture of cement, water, fine aggregate (sand) and coarse aggregate, most often crushed stone or gravel. Plasticizers and other admixtures may be added when needed to adjust workability, setting time, frost resistance or ease of placement.

The main characteristic of concrete is compressive strength, measured in megapascals (MPa). In technical practice, concrete is designated by classes, for example B7.5–B80, while household recipes often use grades such as M100, M150, M200, M300 and higher. For home preparation, it is important to know the task in advance: a blinding layer, path, screed, foundation or other product requires different proportions and different strength.

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 coarse aggregate: crushed stone or suitable gravel. For home work, clean aggregate of about 5–20 mm is often used, and in some tasks up to 5–35 mm. The quality of such concrete directly depends on the mix composition, aggregate grading and cleanliness of all 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 — about 10 percent loss of strength.
• More than 2 months — about 20 percent loss.
• More than 6 months — about 30–50 percent loss.
• 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 coarse aggregate. Crushed stone is often preferred because its rough, angular surface bonds better with cement paste. Rounded gravel can also be used in concrete, but the mix design and strength requirements should be considered separately. For household mixes, aggregate sizes from 5 to 20 mm or up to 35 mm are usually used. The aggregate should contain as little dust and clay contamination as possible.

The fourth component is water. Use only clean water without oils, silt, organic contamination or aggressive impurities. The amount of water should be controlled not “by eye”, but by the water-cement ratio: for ordinary concrete mixes it is often roughly in the 0.4–0.6 range by mass. Excess water increases porosity and reduces concrete strength, while too little water makes mixing and placing difficult. The practical rule remains simple: if the water is suitable for drinking, it is usually suitable for making 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 approximate proportion tables for M400 and M500 cement, sand and crushed stone for common concrete grades. These tables are suitable for preliminary calculation, but for load-bearing or responsible structures the mix design should be checked against the project, standards and actual material properties. M400 cement:

M500 cement:

Following the proportions helps obtain concrete with the required density and strength. At the same time, the real properties of the mix depend on sand moisture, crushed stone fraction and cleanliness, cement activity, water amount and compaction quality.

Mixing concrete

Here the main rule is simple: small non-critical batches can be mixed by hand, but it is difficult to achieve stable uniformity this way. For foundations, screeds, slabs and other responsible pours, it is better to use a concrete mixer: long pauses, poor mixing and uneven water distribution can noticeably reduce the strength of the finished concrete.

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 hardening and protection, concrete should be covered with film or another moisture-retaining material. During the first days, it is important to prevent the surface from drying too quickly: proper moist curing reduces the risk of cracks and helps concrete gain strength.

It is usually possible to walk carefully on a small layer after initial hardening, but the exact time depends on the mix, temperature and placement thickness. Design strength is usually assessed at 28 days. With favorable moist curing, strength gain can continue afterwards, so for important work the timing of form removal and loading should be selected according to the project, curing conditions and requirements of the specific mix.