What is floor expansion joint?

What is a concrete floor expansion joint and why is it necessary?

Concrete screeds and screeds may appear hard, stable, and unchanging. In reality, however, these are materials that "work" and live throughout the life of the building. A floor expansion joint is simply a deliberately designed gap (a gap) that allows individual structural elements to move independently. This prevents unrelieved stresses from damaging the material.

What is the engineering definition of a floor expansion joint?

Technically speaking, an expansion joint is a deliberate gap. It divides a building or a specific element of it—in this case, the floor—into smaller, independent sections of flooring. Its main function is to absorb and compensate for material deformations. This prevents destructive stresses from transferring to other parts of the structure. This creates an expansion joint that protects the entire investment.

What physical phenomena do expansion joints in the floor compensate for?

Epoxy or polyurethane resin floors and other building materials constantly change their volume. Expansion joints allow them to combat three main forces:

• Thermal expansion: When a material expands due to temperature changes, it needs space, if we do not provide it with space, the floor will buckle;
• Concrete shrinkage: During the setting process (hydration), concrete loses water, which causes it to shrink, this is a natural process - without the cuts, it would lead to the formation of uncontrolled cracks and fissures;
• Rheological deformation: This is the long-term change in the shape of a material under the influence of a constant load, known as creep.

Why is an expansion joint not a defect but a planned element of the structure?

Investors often ask if it's possible to pour the floor "smoothly." The answer is simple: no, if we want to avoid disaster. Expansion joints are essential and act as a safety valve.

Important: A crack in concrete will develop anyway – it's inevitable. A floor expansion joint is simply a crack that we, as engineers, induce in a precisely controlled location and in an aesthetically pleasing manner. The alternative is to allow nature to destroy the floor at a random point.

What are the types of expansion joints: structural, surface and indirect

Not every expansion joint serves the same function. There are several key types that must be considered in the design of a thin-layer commercial cement floor. They are often divided into surface joints and structural joints.

What is the difference between thermal and technological expansion joints?

• Thermal expansion joint (compensation): We use it to compensate for movements resulting from temperature changes, it is crucial for underfloor heating and outdoor use;
• Technological (working) expansion joint: This results from the construction process itself. If pouring a huge hall in one day is impossible, the place where the "old" and "new" concrete joins becomes a technological expansion joint.

When to use structural expansion joints and when to use perimeter expansion joints?

The table below illustrates the differences between these two fundamental types:

Type of expansion joint	Function	Place of application
Construction	It separates distinct elements of a building's structure (e.g., foundations). It cuts through the entire cross-section of the structure—walls, ceilings, and floors. It is crucial in areas at risk of mining damage.	Building connections, settlement expansion joints.
Perimeter (border)	It separates the floor from fixed elements. It often occurs as a floor expansion joint next to a wall, providing freedom of movement.	Along walls, around columns and pipes.

There is also a so-called indirect expansion joint, which cuts only part of the thickness of the board, as opposed to a full construction joint.

What are the functions of anti-vibration and acoustic expansion joints?

In industrial halls where powerful machinery operates, vibration-damping industrial floor expansion joints are essential. They isolate the machine's foundation to prevent vibrations from damaging the structure. In residential buildings, on the other hand, perimeter expansion joints serve an acoustic function.

What materials, strips and profiles are used to make floor expansion joints?

Simply creating expansion joints isn't the end of the job – they must be secured. Expansion joint systems or flexible fillers are often used.

Which sealing materials are the most durable and most commonly used?

To fill gaps in polished concrete floors, i.e. in expansion joints, permanently elastic masses are most often used:

• Polyurethane: The King in Industrial Applications (Industrial Flooring);
• Epoxy Resin (Flexible): Where edges need to be firm;
• Silicone: The domain of residential construction, especially in bathrooms where ceramic tiles are used.

How to choose the right expansion profile for the type of flooring?

Where traffic is heavy, mass alone is not enough. System expansion profiles can be used:

• Aluminum/Steel Profiles: Standard in Galleries;
• Sinusoidal profiles: Protect the concrete edge from being chipped by trolley wheels.

Sometimes it's necessary to install such a profile in an existing concrete floor. In this case, it's helpful to mill the concrete, thus creating a trench. The profile is then installed and filled with quick-setting mortar. Next, we need to grind the concrete.

What are the modern material solutions for expansion joints?

Expansion tapes and polyethylene cords are also used. These ensure that the sealant in the gap works properly, adhering only to the sides. A finishing strip, in turn, is often used to conceal expansion joints in the top layer (e.g., when connecting a panel to tiles).

How to properly perform concrete floor expansion joints step by step?

To properly perform a floor expansion joint, precision is key. Mistakes are difficult to correct.

What are the stages of performing contraction dilation?

• Planning: Divide the floor into fields. Fields should be no larger than 6x6 m (a maximum of 8 m per side is often assumed, but less is recommended), and the aspect ratio should not exceed 1:1.5;
• Pre-cutting: Cuts are made in the fresh concrete, creating an expansion joint;
• Curing: Concrete shrinks;
• Expanding and sealing: The joint is filled after shrinkage has finished.

When and how to cut expansion joints in fresh concrete?

Timing is key – typically 24-48 hours after pouring. The cutting depth should be 1/3 to 1/4 of the concrete slab's thickness.

How to properly fill and seal an expansion joint?

The joint must be dry. The concrete floor expansion joint must have a mass arranged to form a concave meniscus, protecting the edges.

Floor expansion joints at the wall, expansion joints on the balcony and terrace, and underfloor heating

The use of expansion joints depends on the location (wall, floor, terrace).

What expansion joints are required in residential buildings?

The most important thing is the expansion joint between the floor and the wall (perimeter joint). Often, it's enough to leave a gap filled with foam around the perimeter, separating the screed from the wall. The expansion joint between the screed and door thresholds is equally important.

In a floor with underfloor heating, it is necessary to divide the surface. Expansion joints prevent pipes and screed from cracking under the influence of heat.

Expansion joint on the balcony and terrace – why is it crucial?

Expansion joints on balconies and terraces are an absolute necessity. Temperature variations here are enormous. Lack of appropriate expansion zones (usually a maximum area of 3x3 m) will result in tiles falling off and cracking of the subfloor. This protects tile floors from cracking.

How to design expansion joints in industrial halls?

Here, the priority is load resistance to avoid the need for subsequent floor repairs. Floor expansion joints must withstand heavy traffic. In industry, concrete subfloors are divided into smaller sections, and armored profiles are used at critical points.

Properly executed concrete floor expansion joint – benefits

• Durability: Properly executed expansion joint prevents the floor from cracking randomly;
• Safety: No faults, floor cracks are eliminated;
• Aesthetics: The aesthetics of the floor are not disturbed by wild scratches; straight dividing lines look professional;
• Finish protection: Protects ceramic tiles and other surface layers from damage at the floor interface.

Lack of expansion joints and cracks in the floor – the consequences of errors

What are the consequences of missing or incorrect floor expansion joints?

Missing expansion joints is a surefire path to disaster. It's estimated that most damage is caused by improper expansion joints. This can mean serious damage to the flooring material.

What problems arise without proper expansion joints?

• Keying of boards: Irregularities at the joints;
• Edge damage: Concrete spalling;
• Uncontrolled cracks: Floor cracks can appear in the middle of a living room or hall.

Repairing the damaged surface and reconstructing the floor itself is significantly more expensive than installing the original, correct expansion joint. To avoid the need for repairs to the building's walls and pillars, use safety barriers.