Repairing and screeding of slab edges with flowable structural repair mortar

Descripción sistema

The edge or end of a slab, known as the slab edge, is an element of the structure that must be correctly aligned with an imaginary straight vertical line, a criterion that obeys aesthetic reasons for the building, but also the need to function properly as a support for certain types of façade.

In renovation works it is common to observe that this is not always the case and that, when the level is pulled down, some of the floor slabs are removed from, or exceed, this vertical.

This was the problem in the building in which Molins intervened, in which the edges of the slab were covered with an L-shaped artificial stone cladding.

Reason for the intervention

Due to the passage of time and the action of the weather, the reinforced mortar used in previous works to increase these slab edges showed signs of degradation. Bearing in mind that the stone cladding rested not only on the upper part of the slab, but also on these mortars, it was clearly necessary to ensure its adherence.

To carry out the repair, the cladding pieces were first removed. Some of them were left unusable in the operation, but they could be replaced with the help of a specialised company, which was able to adjust them sufficiently so that the colour difference between the old and new stones was practically imperceptible.

The floor slabs in this project did not extend beyond the façade line, but all of them had to be repointed with the appropriate mortar after removing the mortar that was in poor condition.

Challenges and constraints

“Use as screed mortar a high-strength, non-shrink mortar that allows for strong continuity of the slab in the aligned area.
“The mortar must allow for screeds between 10 and 15 cm thick.
“Ensure the mechanical and chemical adherence of this mortar to the old slab.
“Ensure the mechanical and chemical adherence of the stone cladding to the repaired slab edges.

Molins Solution

“Installation of rebar anchored to the original slab edge with PROPAM® NF EPO, once the old screed mortar has been removed.
“Application of BETOPOX® 93 bonding bridge on the surface of the slab edge.
“Application by pouring PROPAM® REPAR TECHNO FLUID mortar into the formwork.
“Laying of the stone cladding with VAT® FLEXIBLE adhesive.
“Additional fixing of the stones to the substrate with PROPAM® NF EPO.
“Grouting of the stones with BORADA® UNIVERSAL special joint mortar.

Execution

“1. Removal of the stone cladding, and repointing of the old screed mortar.

“Installation of the reinforcing bars by fixing them to the concrete substrate with the high-performance epoxy-acrylate resin for structural chemical anchoring PROPAM® NF EPO (ETA certified according to ETAG 001 part 1 and part 5 in concrete). Drilling into the substrate is carried out using a mechanical drill with a hammer, followed by blowing to prevent residual dust from affecting the resin anchorage.

“3. Installation of the formwork and sealing of the joints with BETOFLEX MS (single-component, high-performance elastomeric sealant based on MS polymer that meets the requirements of standards EN 15651-1, EN 15651-3, and EN 15651-4) to prevent mortar leakage.
“4. Application of BETOPOX® 93, a two-component bonding bridge based on low-viscosity epoxy resins, on the surface of the slab edge at a rate of 150 g/m2. This product meets the requirements of EN 1504-7.
“5. Pour into the formwork, while the bonding bridge is still fresh, the very high mechanical strength, non-shrink, fibre-reinforced, fluid mortar, PROPAM® REPAR TECHNO FLUID. This mortar meets the requirements of EN 1504-3 class R4, EN 1504-2 and EN 1504-7. It can be used for structural screeds between 20 and 200 mm.

“After 24 hours, the formwork is stripped and the mortar is cured by wetting it with water frequently during the first 48 hours.

“The scheduling of the work according to a sequence of works that included first of all the alignment of all the slabs, allowed the setting and hardening process of the PROPAM® REPAR TECHNO FLUID mortar to be completed and, consequently, the stone covering to be placed on a safe support using the VAT® FLEXIBLE cementitious adhesive (C2TES1 according to EN 12004).
“Once the VAT® FLEXIBLE adhesive had hardened and as an additional safety supplement, the individual pieces were mechanically fixed individually with the chemical dowel PROPAM® NF EPO, and BORADA® UNIVERSAL (CG2WA according to EN 13888) was used for the grouting of the cladding.

Technical note

PROPAM® REPAR TECHNO FLUID mortar is a new generation mortar that allows all the steps of a structural repair to be carried out with a single product:
” Reinforcement passivation.
“Structural reconstruction in a single layer up to 200 mm.
“Waterproof and smooth finish for increased durability.
The use of a fluid structural repair mortar makes it possible to carry out repairs in high thicknesses with a single application by pouring or pumping into the formwork, so that its high fluidity ensures complete filling of the cavity even when the volume of reinforcement is high.

Its excellent fluidity and low water/cement ratio allow high quality surface finishes to be obtained. With this mortar, repairs are obtained that improve the resistance to carbonation and to the penetration of aggressive agents for the concrete, thus increasing the durability of the repair.

Often these types of repairs and formwork screeds are made with concrete or with fluid anchoring mortars (grouts), which have the following disadvantages:

“Concrete easily cracks in high stress areas such as edges and corners because it is not shrinkage compensated.
“Grouts are designed to work in confinement, and are formulated to have a slight expansion to ensure that they completely fill the void in which they are applied. If these mortars are left unconfined, it is easy for them to produce stresses that lead to cracking and lack of adhesion.

PROPAM® REPAR TECHNO FLUID is a non-shrink, fibre-reinforced, but non-expansive, fluid mortar, which allows repairs and screeds to be carried out on formwork without cracking.