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Jan 05

Expansion joint: what is it? which difference with fractional expansion?

The term expansion joint is known to all but is often used wrongly and through. However, it is a very important masonry element, recommended by the UTD in certain contexts and making it possible, in all cases, to permanently preserve the building from variations in temperature and humidity. Definitions, types, standards: all you need to know about the expansion joint..

Concrete, like most materials, reacts to changes in temperature and humidity by expanding or contracting. Therefore, this play creates a movement that must imperatively be compensated if we want to preserve the integrity of the building.
Masons must place an expansion joint every 20 or 35 meters, according to UTD (DTU) 20.1: the expansion joint is therefore for masonry of large (very large) surfaces and should not concern individuals.
But also, expansion joints are placed when constructing adjoining buildings: the masonry of the new construction, under the action of the expansion, would risk pushing the old construction. To avoid this, the masons therefore leave a space of variable thickness depending on the zone of seismicity considered (2 to 4 cm) between the two structures: this is strictly speaking what is called an expansion joint.

Expansion joints are designed to accommodate both expansion and contraction. They can vary in complexity from a simple gap filled with rot-proof compressible boarding (as used in concrete retaining walls, slabs and similar structure), to the complicated roller, rocker or sliding joints provided at the end of bridge or similar beams. Expansion gaps in walls and slabs can be made watertight if necessary by incorporating a suitable water bar and sealant. Expansion joints in buildings must be carefully located and made weatherproof by providing cappings at joints in roofs and in the use of copper water bars or similar methods of sealing vertical walls. Care must be taken with the treatment of internal finishes at the positions where expansion joints are located, plates being used on the floors and cover strips or other features being used on walls or ceilings to permit sliding and prevent cracking of plaster or other finishings.

It should be noted that construction joints are not considered to be movement joints. They are introduced to divide the structure into conveniently sized sections for casting. The reinforcement is continuous across the joint and the face of the joint is prepared to encourage continuity of the concrete. In practice, however, shrinkage frequently occurs at construction joints converting them effectively into contraction joints. 

Fractional joints
Conversely, when a joint is left, generally using a PVC profile, in large-area masonry, it is rather referred to as a fractionation joint, even if the latter has essentially the same purpose. But if, in the case of terraced constructions, the expansion joint is intended to protect the old building from the expansion / retraction effects of the new building, the fractionation joints are intended to prevent cracking of large masonry. surface: all parts of the masonry that do not dry at the same speed.
We also speak of expansion joint for screeds, slabs and tiling on surfaces greater than 40 m². In reality, we should here again rather speak of a fractionation joint. But whatever. These expansion joints have exactly the same function: to prevent cracking of the screed / slab or the loosening of the tiling tiles: on surfaces greater than 40 m², expansion / retraction play of mortar, glue, etc. would risk causing weaknesses in the implementation.

For paving on full ground, we are used to sawn the slab, to anticipate the movement and cause cracks in these saw cuts;
For laying tiles on large surfaces, aluminum or PVC profiles or silicone joints 10 to 20 mm wide are regularly inserted to ensure the function of expansion joints.
The problem is that determining the location of expansion joints, their regularity and spacing depends directly on the type of screed / slab, the laying conditions and the climate of the region. This is why it is strongly recommended, to guarantee the durability of the building and the work carried out, to entrust the task of the expansion joints to trained and competent professionals who, alone, will be able to find the ideal compromise to achieve in accordance with the rules of the 'art the desired work.

Expansion joint 04


Expansion joint 11 



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