Lifting the slab on the ground

Here is the second part concerning the problems affecting the slabs on the ground. In my first article, it was about cracks in the slab on the ground, while I will deal in this one with the lifting of the slab.

The presence of cracks, efflorescence and damage in the floor tile often indicates that the floor tile has been subjected to a long period of moisture. The latter could have been caused by hydrostatic pressure in connection with poor drainage of the foundations, a negative slope towards the building or because of the lack of clearance between the garage wall and the adjacent floor.


Pyrite can also cause damage, cracking and lifting of the slab on the floor. It should be noted that the pyrite occurs due to the phenomenon of swelling of the embankment under the structure of the building. By definition, pyrite is an iron sulfide mineral found in shale. The latter is a soft sedimentary rock that looks like clay. In fact, this type of rock can be used to produce the embankments necessary in the field of residential construction. In fact, these embankments have often been used below concrete slabs in basements and garages.

Humidity and oxygen, under specific conditions, trigger the oxidation of the mineral iron sulphide (pyrite) in the embankment. Chemical reactions, which occur in pyrite, cause the embankment to swell. Then, the backfill pushes the concrete slab vertically and produces swellings in the slab on the ground. The chemical reaction (sulfation) - resulting in the swelling of the concrete slab - also attacks the concrete of the slab which becomes brittle and loses its solidity and its integrity. 

Anal Fissure star and slab swelling on the ground 

Thus, star-shaped cracks and swelling in the slab on ground in the basement and in the garage can be caused by:

  1. Pyrite - The only method to precisely check the presence of pyrite shale (pyrite), in the embankment under the concrete floor, is to have this embankment analyzed by a specialized laboratory.
  2. Concrete sulfation - the presence of moisture, under the slab, connected to poor drainage can cause the sulfation of concrete.
  3. Hydrostatic pressure - As for hydrostatic pressure, poor drainage of the foundations can create hydrostatic pressure under the slab on the ground.

Poor foundation drainage

In the same vein, a poor drainage engines of the foundations can be caused by:

  1. A negative slope from the ground (slope) to the building. This situation abnormally requests the drainage of the foundations. You have to change the slope of the land to keep the water away from the building.
  1. Un French drain inadequate (crushed, negative slope, etc.) can also cause hydrostatic pressure under the slab.

"Slab on ground" items

Star-shaped crack caused by lifting the slab from the ground

Star-shaped crack caused by lifting the slab from the ground

Hydrostatic pressure and swelling of the slab on the ground

Hydrostatic pressure and swelling of the slab on the ground