Larsen FiberFlex™ Rapid Set+ 20kg
Professional S1 Flexible Tile Adhesive
Larsen FiberFlex™ Rapid Set+ combines fast setting with increased flexibility.
Its C2 F S1 classification provides enhanced adhesion, rapid setting and S1 deformability.
Therefore, it works especially well where a standard tile adhesive may not provide enough movement tolerance.
The adhesive suits both professional domestic installations and demanding commercial work.
Ideal for Underfloor Heating
FiberFlex™ Rapid Set+ works with correctly prepared underfloor heating systems and heated screeds.
Heated floors expand and contract as temperatures change. Therefore, using a suitable flexible tile adhesive remains important.
The S1 deformable formulation helps accommodate movement within the installation.
Always commission and prepare the underfloor heating system according to Larsen’s current technical instructions before tiling.
Suitable for Porcelain and Large Tiles
Modern porcelain and large format tiles need strong, consistent adhesion.
FiberFlex™ Rapid Set+ suits:
- Porcelain tiles
- Ceramic tiles
- Natural stone
- Glass mosaics
- Large format tiles
For large format tiles, apply a thin layer of adhesive to the back of each tile as well as the prepared substrate.
This helps achieve full adhesive contact.
Rapid Setting Performance
The adhesive sets quickly, so projects can move forward sooner.
Under suitable conditions, installers can normally grout after approximately three hours.
Light foot traffic can also begin after approximately three hours.
However, temperature, substrate condition and application depth can affect setting times.
Approximately 45-Minute Pot Life
Once mixed, FiberFlex™ Rapid Set+ has a working pot life of approximately 45 minutes at 20°C.
Therefore, only mix an amount that can be comfortably used within the available working time.
Warmer conditions can shorten working time. Meanwhile, colder conditions may slow setting.
3-12mm Normal Bed Thickness
The recommended normal adhesive bed is 3mm to 12mm.
However, installers can use the adhesive up to 20mm in small isolated areas where required.
This makes FiberFlex™ Rapid Set+ suitable for many different wall and floor tiling applications.
20kg Professional Bag
Each bag contains 20kg of cement-based adhesive.
Mix one 20kg bag with approximately 4.5 litres of clean water.
Always use clean mixing equipment and measure the water accurately.
Do not add extra water once the adhesive begins to set.
Approximately 4m² Coverage
One 20kg bag covers approximately 4m² at a 3mm adhesive bed.
Actual coverage depends on:
- Trowel size
- Tile size
- Substrate condition
- Adhesive depth
- Application method
- Back-buttering requirements
Therefore, allow for additional material when working on uneven substrates or large format tiles.
Internal and External Use
FiberFlex™ Rapid Set+ suits both internal and external applications.
It can be used on correctly prepared:
- Internal floors
- Internal walls
- External floors
- External walls
- Heated screeds
- Cement-based screeds
- Suitable timber installations
- Swimming pool installations
- Underfloor heating systems
Correct substrate preparation remains essential for every installation.
Suitable for Swimming Pools
Larsen approves FiberFlex™ Rapid Set+ for demanding applications such as swimming pools.
However, the substrate must receive the correct preparation and waterproofing before tiling.
Wet areas also require an appropriate tanking system where applicable.
Timber Floor Installations
FiberFlex™ Rapid Set+ can form part of a correctly prepared timber floor installation.
However, the timber structure must remain rigid and properly supported.
Do not tile directly onto plywood or other wood-based boards.
Instead, use a suitable intermediate surface such as a tile backer board, uncoupling membrane or approved reinforced tanking system.
Our Kudos Trading Tile Backer Board 10mm provides a practical tiling surface for many suitable installations.
Correct Floor Preparation
The substrate must remain clean, stable and suitably dry.
Remove:
- Dust
- Grease
- Oil
- Loose material
- Surface contamination
- Standing water
Correct preparation improves adhesion and helps achieve a dependable tiled finish.
Use the Correct Primer
Some surfaces require priming before applying the tile adhesive.
For porous substrates, use Larsen Acrylic Floor Primer 1L where specified.
For smooth or low-absorbency surfaces, Larsen Prime Grip 360 can provide a textured mechanical key where appropriate.
Always follow Larsen’s substrate preparation instructions.
Solid-Bed Floor Tiling
For floors, wet areas and external installations, use a solid-bed fixing method.
This helps prevent voids behind the tile.
Voids can weaken the finished installation. In addition, they can create problems under heavy loads or external temperature changes.
Large format tiles should also receive a thin skim of adhesive on the tile back.
Ideal for Fast-Track Tiling
Rapid-setting adhesive allows installers to continue with the next stage sooner.
As a result, FiberFlex™ Rapid Set+ works particularly well for:
- Bathrooms
- Kitchens
- Extensions
- Renovations
- New builds
- Underfloor heating projects
- Commercial floors
- Large format tiling
- External tiling
- Swimming pool installations
Key Features
- Professional Larsen Pro Red Bag
- 20kg pack
- Fully flexible S1 adhesive
- C2 F S1 classification
- Rapid-setting formulation
- Enhanced adhesion
- Approximately 45-minute pot life
- Grout after approximately three hours
- 3-12mm normal bed thickness
- Up to 20mm in isolated areas
- Approximately 4m² coverage at 3mm
- Suitable for porcelain tiles
- Suitable for ceramic tiles
- Suitable for natural stone
- Suitable for glass mosaics
- Suitable for large format tiles
- Internal and external use
- Wall and floor applications
- Suitable for underfloor heating
- Suitable for heated screeds
- Suitable for correctly prepared timber installations
- Suitable for swimming pools
Technical Specifications
| Specification | Details |
|---|---|
| Brand | Larsen Building Products |
| Product | FiberFlex™ Rapid Set+ |
| Range | Professional / Pro Red Bag |
| Pack Size | 20kg |
| Product Type | Flexible Rapid-Set Cement-Based Tile Adhesive |
| Classification | BS EN 12004 C2 F S1 |
| Flexibility | S1 Deformable |
| Normal Bed Thickness | 3-12mm |
| Maximum Localised Depth | Up to 20mm |
| Mixing Water | Approx. 4.5 litres per 20kg |
| Pot Life | Approx. 45 minutes at 20°C |
| Grouting | Approx. 3 hours |
| Light Foot Traffic | Approx. 3 hours |
| Coverage | Approx. 4m² at 3mm |
| Application | Walls and Floors |
| Internal Use | Yes |
| External Use | Yes |
| Underfloor Heating | Yes |
| Heated Screeds | Yes |
| Swimming Pools | Yes |
| Tile Types | Porcelain, Ceramic, Natural Stone, Glass Mosaic, Large Format |
| Manufacturer Colours | Grey and White |
What Does C2 F S1 Mean?
The C2 F S1 classification describes the performance of the adhesive.
C2 means enhanced cementitious adhesive.
F means fast setting.
S1 confirms deformability.
Therefore, FiberFlex™ Rapid Set+ suits demanding installations where strong adhesion, faster setting and additional flexibility matter.
Why Buy From Kudos Trading?
Kudos Trading supplies Larsen products alongside a complete range of floor preparation and underfloor heating materials.
Therefore, installers can order primers, levelling compounds, tile backer boards and heating components from one supplier.
We have supplied underfloor heating products to the UK since 2001. In addition, our experienced team can help with complete water underfloor heating projects.
Frequently Asked Questions
What Is Larsen Pro Red Bag?
Larsen Pro Red Bag is FiberFlex™ Rapid Set+.
It is a fast-setting, fully flexible S1 tile adhesive for demanding wall and floor applications.
Is Larsen FiberFlex Rapid Set+ Suitable for Underfloor Heating?
Yes.
Larsen approves FiberFlex™ Rapid Set+ for correctly prepared underfloor heating systems and heated screeds.
Is It S1 Rated?
Yes.
FiberFlex™ Rapid Set+ meets BS EN 12004 C2 F S1 classification.
How Soon Can I Grout?
Under suitable conditions, tiles can normally be grouted after approximately three hours.
Site temperature and substrate conditions can affect this time.
How Long Is the Working Time?
The mixed adhesive has a pot life of approximately 45 minutes at 20°C.
Therefore, avoid mixing more than you can apply during that period.
How Much Water Do I Need?
Use approximately 4.5 litres of clean water per 20kg bag.
Always follow Larsen’s current mixing instructions.
What Is the Recommended Bed Thickness?
The normal bed thickness is 3-12mm.
Small isolated areas can reach up to approximately 20mm where required.
How Much Area Does One Bag Cover?
One 20kg bag covers approximately 4m² at a 3mm bed thickness.
Actual coverage will vary according to the substrate and installation method.
Can I Use It with Porcelain Tiles?
Yes.
FiberFlex™ Rapid Set+ suits porcelain, ceramic, natural stone, glass mosaics and large format tiles.
Is It Suitable for Outside?
Yes.
The adhesive suits correctly prepared external wall and floor installations.
Can It Be Used in Swimming Pools?
Yes.
Larsen lists swimming pools as a suitable application.
However, correct waterproofing and substrate preparation remain essential.
Can I Tile Directly onto Plywood?
No.
Larsen advises against tiling directly onto plywood or other wood-based boards.
Use a suitable tile backer board, uncoupling membrane or approved intermediate system.
Is It Suitable for Large Format Tiles?
Yes.
For large format tiles, fully skim the back of the tile with adhesive before fixing.
This helps achieve adequate adhesive contact.
Related Products
- Larsen Acrylic Floor Primer 1L
- Larsen Prime Grip 360 1kg
- Larsen SLC 1550 Flex 20kg
- Kudos Trading Tile Backer Board 10mm
- Tile Backer Board Fixing Kit – 100 Screws & Washers
- Levelling Compound & Tile Adhesives
- UFH Laying Systems & Insulation
Next Working Day Delivery: Yes, we hold all our products in stock at our 7000 sq ft Nottingham warehouse and at our 3000 sq ft warehouse in Market Harborough and use DPD for a tracked next-day delivery.
Collection Available: You can always collect from our Norttinagham location and help yourself to a free tea and coffee.
