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F Ball and Co’s Stopgap SRS offers cost-effective solution for weak and friable screeds

When preparing to install floorcoverings, contractors sometimes discover that the concrete or sand and cement subfloor is weak or friable – often the result of poor installation or curing techniques.

Previously, a weak or damaged screed would have to be entirely removed by mechanical means and a new screed installed. Now, providing the subfloor is in a reasonable condition, contractors have a less costly and disruptive option: in most cases, a weak or friable screed can be prepared with a surface reinforcement system (SRS), such as F Ball and Co’s Stopgap SRS.

Says the company: ‘The two-component epoxy resin reinforcement material is designed to quickly stabilise and reinforce weak sand/cement or calcium sulphate screeds. Contractors simply mix the components thoroughly, pour the mixture over the weak subfloor and spread out with a rubber squeegee, working into the surface until no more liquid is absorbed.

‘The product penetrates the weak/friable surface, filling voids and cracks and binding loose particles to strengthen the screed.’

Case study
This was the recommendation when one of F Ball’s regional technical representatives was called to give advice on remedial action where a luxury vinyl tile (LVT) installation throughout the ground floor of a newbuild residential property had begun to debond from the subfloor.
The area totaled about 65sq m and included the lounge, hall, open-plan kitchen and dining room, utility room and WC.

On the removal of floorcoverings, a layer on the underside was visible that was consistent with laitance, the crust of fine particles formed on the surface of a screed as it dries. This should have been removed and was doubtless a factor contributing to the floor failure. Under the laitance, the 75mm-thick concrete base was weak and sandy and could easily be scratched away to reveal the aggregate.

Added to that, an indicative moisture test showed that subfloor moisture levels were around the threshold for floorcoverings being installed and risking excess subfloor moisture attacking adhesives and causing floor failure. BS 8203, Code of practice for installation of resilient floorcoverings Annex B states that resilient floorcoverings shouldn’t be installed where humidity levels in the subfloor are above 75% relative humidity without a moisture management solution in place.

Based on the above information, the technical representative was able to recommend that the layer of laitance was first removed, along with any surface contamination, by mechanical means, and vacuumed to leave a smooth, clean surface. F Ball’s Stopgap SRS surface reinforcement system could then be used to strengthen the concrete surface.

Contnues the company: ‘The product acts rapidly, meaning weak screeds can be reinforced overnight to provide a base suitable for the receipt of other subfloor preparation products. It can also be used over certain screeds containing high levels of construction moisture prior to the application of a waterproof surface membrane.’

Depending on how weak or porous the screed appears, contractors could conduct a test to determine the likelihood of success prior to the use of a surface reinforcement system. In Situ Crushing Resistance (ISCR) tests, using a BRE screed tester to BS 8204, are typically used for these purposes. This test should not be undertaken where an underfloor heating test is present as this could risk damaging the system in place.

Moisture management
Continues F Ball: ‘Within 24 hours of Stopgap SRS curing, F Ball’s Stopgap F77 waterproof surface membrane could be applied to the surface and rolled with a roller that has been coated with the liquid to achieve a continuous, pin-hole free finish, before allowing it to cure.

‘It was recommended that the surface was then primed using F Ball’s Stopgap P141, which is designed to create a textured finish to enhance bond performance between levelling compounds and non-absorbent surfaces, such as epoxy waterproof surface membranes.’

Final steps
Flooring contractors could then apply a suitable floor levelling compound to create a perfectly smooth base for floorcoverings and optimise the appearance of the finished installation.

Finally, it was advised floorcoverings were installed using a compatible adhesive. Where LVTs will be installed in areas where high temperatures and extreme temperature fluctuations are likely, such as in the kitchen-dining room with patio doors, potentially resulting in solar gain, the use of a temperature tolerant, pressure-sensitive adhesive, such as F Ball’s Styccobond F49 Hybrid PS, is recommended by F Ball.

Says the company: ‘The solvent-free, water-based adhesive develops the ultra-high bond strength to hold floorcoverings firmly in place when exposed to temperature fluctuations from -20deg C up to +60deg C. The pressure sensitive characteristics of the adhesive, crucially high initial tack, would also help with the positioning and alignment of floorcoverings.’

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