A garage is not just a place to store a car, but a full-fledged workshop and maintenance area, where the flooring experiences enormous loads. The weight of a modern sedan or SUV, coupled with possible impacts from falling tools and exposure to aggressive technical fluids, requires exceptional foundation strength. That is why the question of how to make a floor screed in a garage is faced by every owner who wants to ensure the durability and safety of their premises.
Poorly performed work can lead to the formation of cracks, dust and destruction of the top layer after just a year of operation, which will require expensive repairs. In this article we will analyze in detail all the stages of creating a reliable concrete foundation, from soil preparation to finishing. You will learn what materials to choose, how to correctly calculate the proportions and why reinforcement is a critical step that cannot be ignored.
Selection of technology and calculation of materials
Before starting work, it is necessary to decide on the type of structure, since the load-bearing capacity of the future floor depends on this. For a garage, the most suitable option is a monolithic concrete slab, which is laid directly on the prepared soil base. It is important to understand that the usual cement-sand mixture, used in apartments, is not suitable here due to insufficient compressive and bending strength.
Calculating the quantity of materials is not just a formality, but a necessity to avoid stopping work in the middle of the process. Concrete for a garage must have a grade of at least M300, which corresponds to strength class B22.5. If you plan to use heavy equipment or store large cargo, the requirements for brand of concrete are increasing.
To prepare the solution yourself, you will need Portland cement M400 or M500, purified sand and crushed stone of a fraction of 5-20 mm. Proportions are key: imbalance of water and cement will either lead to brittleness or excessive shrinkage and cracks.
⚠️ Attention: The use of sea sand or sand with clay impurities is strictly prohibited, as this will drastically reduce the strength of the finished structure and lead to delamination of the screed.
The secret of durable concrete
Plasticizers added to the solution make it possible to reduce the water-cement ratio, increasing the final strength and water resistance of concrete without losing its mobility during laying.
Foundation preparation and excavation work
The quality of the “cushion” preparation determines whether your floor will walk or stand as a monolith for decades. First, the top fertile layer of soil is removed, as organic matter rots over time, forming voids and causing subsidence. The excavation depth is calculated taking into account the thickness of all layers: crushed stone, sand, waterproofing and the concrete layer itself.
After excavating the soil, the bottom of the pit must be thoroughly compacted. For this, it is best to use a vibrating plate, but if it is not available, you can get by with a manual log rammer with a transverse handle. A dense base will prevent uneven settlement, which is the main cause of cracks.
Next, a multilayer bedding is formed. The first is a layer of crushed stone 10-15 cm thick, which serves as drainage and distributes the load. A layer of sand 5-10 cm thick is poured onto the crushed stone. Each layer must be spilled with water and compacted to a “stone” density.
☑️ Checking the readiness of the base
Waterproofing and floor insulation
Concrete has a porous structure and is capable of drawing moisture from the ground, creating dampness in the garage, which is detrimental to the metal body of the car. Therefore the device is reliable waterproofing is a mandatory step. Most often, dense polyethylene film with a thickness of at least 200 microns or specialized membranes are used for these purposes.
The film is overlapped by 15-20 cm, and the joints must be taped with wide construction tape. The edges of the waterproofing should extend onto the walls above the level of the future screed. This will create a “trough” effect, protecting the concrete from capillary rise of moisture.
If the garage is heated or you plan to use it as a workshop all year round, it makes sense to lay a layer of insulation. The optimal material is extruded polystyrene foam (XPS), which is not afraid of moisture and has high compressive strength. The thickness of the slabs is usually 50 mm.
| Material | Layer thickness | Function | Features |
|---|---|---|---|
| Crushed stone | 10-15 cm | Drainage, load distribution | Fraction 20-40 mm |
| Sand | 5-10 cm | Leveling, shock absorption | Coarse grain, no clay |
| PVC film | 0.2 mm | Waterproofing | Overlapping |
| Expanded polystyrene | 50 mm | Thermal insulation | For heated garages only |
Reinforcement: creating the skeleton of the structure
Concrete has excellent resistance to compression, but is extremely weak in tension. The garage floor constantly experiences tensile stresses due to uneven loads from the car's wheels. To compensate for this, it is necessary reinforcing mesh. The use of reinforcement increases the strength characteristics of the screed significantly.
For a garage, a metal mesh made of a rod with a diameter of 5-8 mm with a cell of 100x100 mm or 150x150 mm is optimal. It is important that the reinforcement is located inside the concrete layer and not lying on the ground. For this purpose, special plastic clamps or “chairs” are used, which lift the mesh 2-3 cm above the waterproofing.
When laying the mesh, the sheets should overlap each other by at least one cell, and at the joints it is better to tie them with wire. If you plan to park a heavy SUV or minibus, it is better to use double reinforcement or a thicker rod with a diameter of 10-12 mm.
⚠️ Attention: Never lay reinforcing mesh directly on waterproofing or soil - it must be completely immersed in concrete, otherwise the metal will begin to corrode and lose its properties.
Installation of beacons and preparation of solution
To get a perfectly flat surface, you need to install lighthouses. These are the guides along which the rule will move when leveling the mixture. Steel pipes, drywall profiles or special reference beacons can be used as beacons.
The beacons are aligned on a laser level strictly parallel to each other at a distance slightly less than the length of the rule. It is best to fix them on small piles of thick cement mortar, so as not to damage the waterproofing by drilling. After the solution has hardened, the beacons are ready for use.
Preparing a concrete mixture is a process that requires precision. If you use a concrete mixer, first add water, then add crushed stone and some sand, and only finally add cement. The consistency of the finished solution should resemble thick sour cream: it should not be too liquid so as not to shrink too much, but not too dry so that it can be leveled.
To facilitate leveling, add fiber fiber (polypropylene fiber) to the solution - it will prevent the appearance of microcracks during drying and make the surface smoother.
Pouring screed and finishing
Filling is best done in one step to avoid the formation of cold seams, which are weak points of the structure. Unload the concrete between the beacons and immediately spread it with a shovel, filling all the voids. Then, using a long rule, leaning on the beacons, pull the mixture towards you, removing the excess.
After the initial setting, when you can already walk on the floor, leaving only small traces, it is necessary to perform ironing. To do this, dry cement is scattered onto the surface in a thin layer and rubbed in with a trowel or trowel. This creates a durable, non-dusty crust that is resistant to abrasion.
After a few hours, when the concrete has finally “set”, expansion joints need to be cut. They prevent random cracking due to thermal expansion. The seams are cut with a grinder with a diamond blade to a depth of about 1/3 of the thickness of the screed in increments of 3-4 meters.
The main secret to a smooth floor is not to walk on fresh concrete unnecessarily and immediately after setting, grout and cut the joints.
Drying and operation
The process of concrete gaining strength lasts 28 days, but primary hardening occurs in the first week. During this period, it is extremely important to prevent rapid evaporation of moisture. If concrete dries too quickly, it will not have time to gain its design strength and will become covered with a network of cracks.
For proper care, the surface must be periodically moistened with water in the first 7-10 days. In hot weather, concrete is covered with plastic film, creating a greenhouse effect. Only after complete drying can you begin installing the racks and driving the car.
Compliance with technology at every stage - from compacting the soil to caring for the finished screed - guarantees that your garage floor will last for decades without repair. Skimping on materials or skipping preparation steps will inevitably lead to problems in the future.
What is the minimum thickness of screed allowed in a garage?
The minimum thickness of a concrete screed in a garage subject to loads from a passenger car should not be less than 10-12 cm. When using mesh reinforcement, a thickness of 8-10 cm is allowed, but for heavy SUVs it is better to focus on 15 cm.
Is it possible to pour screed in an unheated garage in winter?
Strongly not recommended. For normal hardening, cement needs a positive temperature (above +5°C). Winter pouring without warming up and using special anti-frost additives will lead to freezing of the water in the solution and destruction of the concrete structure.
Is it necessary to slope the floor in the garage?
Yes, a slight slope (1-2 cm per 1 meter of length) towards the gate or drainage gutter is desirable. This will make it easy to wash away dirt and remove water that gets inside the room when the snow melts on the car.
What is the best way to cover a concrete floor after drying?
To protect against dust and oils, concrete is best coated with polyurethane or epoxy impregnation. Also popular are special wear-resistant paints for concrete floors or the installation of self-leveling floors with quartz sand.