Compression layer with light structural screed mortar

The home in which Molins products have been applied corresponds to one of these rooms in the house, and is located in a PB+2 building, whose horizontal structure (slabs) is composed of wooden joists and ceramic vault.

Reason for intervention

Within the framework of rehabilitation of the home, which included its structural adaptation, it was determined to lift some areas of the pavement in which defects of important planimetry, to proceed with its repair and leveling.
When carrying out this operation, it is verified that:
» The pavement, made up of unglazed ceramic tile, is placed on a base layer of unreinforced mortar.
» The wooden joists are in apparent good condition, with loss of section in some areas.

Challenges and limitations

» Protect the wood of the joists against the action of environmental humidity.
» Prevent the mixing water of the mortar with which the compression layer is made from affecting the wooden joists.
» Obtain a good physical union between the wooden joists and the compression layer
» Obtain mechanical performance of the compression layer greater than 30 N/mm2 (at 28 days) with an average thickness of 7 cm of lightened mortar.

Molins Solution

» Application of a protective layer of BETOPOX® 93 on the surface of the joists.
» Once the connectors are installed, in order to promote mechanical adhesion between the compression layer and the joists, application of new layer of BETOPOX® 93 with sprinkling of fine natural quartz aggregate while the resin is still fresh.
» Installation of electro-welded mesh for load distribution.
» Pouring of the mortar PROPAM® LIGHTWEIGHT SCREW AR for formation of the compression layer .

Execution

» 1. Cleaning any remaining dust from the surface of the joists, and application of a first layer of BETOPOX® 93, a two-component bonding bridge based on low viscosity epoxy resins, with a dosage of 150 g/m2, which will act as a protective barrier against environmental humidity. BETOPOX® 93 meets the requirements of the EN 1504-7 standard.

» 2.Installation of connectors that allow a better physical union of the joists with the compression layer. Application of a layer of BETOPOX® 93 with a dosage of 200 g/m2, and sprinkling of natural quartz aggregate (0.4-0.9 mm) until saturation, while the resin is still fresh. After 24 hours, sweep the surface to remove any non-adhered aggregate. By preparing the surface of the joist in this way, the grip (mechanical adhesion) of the compression layer to it is favored.

» 3. Fixing the electro-welded mesh (Ø 5 mm, ME 15×30)

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» 4. Pouring the mortar PROPAM® LIGHTWEIGHT AR screed (CT-C25-F5), lightweight micro-concrete, for the execution of structural screeds in thicknesses from 30 to 100 mm. It is 40% lighter than conventional concrete and meets the requirements of the EN 13813 standard.
The final finish has been carried out with a light coating.

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Technical note

The mortar PROPAM® SCROWED LIGHT AR has three fundamental advantages over conventional concrete when it comes to rehabilitating old structures:
» It is 40% lighter, which allows the weight of the structure to be lightened
» It acquires high mechanical resistance in a very short time, allowing execution times to be reduced.
» It requires less thickness than concrete, which which significantly reduces the loss of useful space.

The density of a conventional hardened concrete is around 2 to 2.2 kg/dm3 while the density of the mortar PROPAM® SCROWED LIGHT AR hardened is approximately 1.2 kg /dm3. This lightness together with compressive strengths at 28 days greater than 25 N/mm2 allow structural screeds to be carried out with weights between 40% and 50% lower, and therefore rehabilitate old floors with structural weight problems.
< br>The low density of this mortar is achieved with a careful granulometry of light aggregates, and with the use in its formulation of a perfectly studied combination of fluidizing and aerating additives, which manage to introduce adequately stabilized and unconnected air pores into the mass. , so that durability is not affected since they do not contribute to the diffusion of water or other external agents that degrade the mortar.

The screeds obtained with PROPAM® SCROWED LIGHT AR are also good thermal and acoustic insulators, due to precisely to its content in stabilized air pores. The thermal conductivity (λ) of this screed is 0.4 W/mk.

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