Underfloor heating filler LL 5500

Base 

• Concrete substrate, wood- and gypsum-based boards, insulation board
• The substrate must be clean, solid, and dust-free, and it must be vacuumed.
• Loose layers, cement laitance, and other impurities must be mechanically removed to ensure proper adhesion between the floor screed and the substrate.
• The substrate must be sufficiently strong, stable, and load-bearing.
• The floor must be constructed as a floating, reinforced structure if the substrate consists of weak concrete (tensile strength < 0.5 MPa), wood, or insulation. The floating floor must be separated from the subfloor with Fescon Separation fabric and from vertical structures with Fescon Bordering strip.
• The subfloor temperature must be > +10°C and the relative humidity < 95% RH. The subfloor’s relative humidity affects the drying time of the floor screed.

Priming 

• Priming is carried out according to the instructions for Fescon Adhesion promoter or Flow Primer, depending on the substrate.
• Non-absorbent surfaces (e.g. ceramic tiles, epoxy, metal surfaces) must be pre-treated in accordance with the Primer PLUS instructions.

Instructions for use 

• The working area must be fully protected from wind, drafts, sunlight, and rain.
• During floor installation, the indoor temperature must be between +10°C and +25°C, and the relative humidity must be above 40% RH.
• One 20 kg bag of screed is mixed with 3.0–3.6 litres of clean water.
• Overdosing water is prohibited, as it weakens the strength properties of the screed, increases the risk of separation, and prolongs the drying time.
• LL 5500 must be mixed into a uniform mass using a power drill with a mixing paddle.
• The mixture is applied to the substrate and levelled with a steel trowel.
• Working time is approximately 20 minutes from the addition of water.
• Tools and equipment must be cleaned with water immediately after use.
• Hardened material must be removed mechanically.

Covering 

• Underfloor heating filler LL 5500 can be directly waterproofed using certified products from the Fescon Waterproofing system.
• It can be covered with ceramic tiles, laminate, and parquet.
• Other floor coverings require a skim coat using Fescon hand-applied levelling compounds, such as FlowPlan.
• Layer thicknesses of less than 20 mm can be covered after 24 hours.
• However, it must be ensured that the screed meets the technical requirements set by the floor covering manufacturer and the RYL guidelines, taking into account the entire floor structure. The flatness of the screed surface should be measured, if necessary, in accordance with RT instruction 14-11039.
• The screed must not be left uncoated for more than 3 months due to the risk of cracking and detachment.
• Once the screed has reached the required moisture level for the floor covering, the covering should be installed or post-treatment started.
• Always check the moisture content of the entire floor structure before installing the covering.
• Favourable drying conditions for the screed require indoor air relative humidity below 50% RH and temperature above +20°C. Unfavourable conditions will slow down the development of the screed’s strength properties and extend the drying time.

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