Fosroc Brushbond FLXIII
Two-component polymer-modified elastomeric cementitious waterproofing membrane for concrete and masonry, applied by brush, roller or trowel.
Fosroc Brushbond FLXIII at a glance
The essentials specifiers and contractors ask first — answered straight from the product data, with links to go deeper.
What is it?
Fosroc Brushbond FLXIII is a two-component, polymer-modified, elastomeric cementitious waterproofing membrane. A factory-blended cement-and-aggregate powder is mixed on site with a liquid polymer component to produce a brushable slurry that cures to a seamless, flexible waterproof coating on concrete and masonry.
Where is it used?
It is used as a seamless waterproof membrane on buried concrete structures such as bridge abutments, culverts, basements and retaining walls, and on non-trafficked reinforced concrete roof decks used in conjunction with a suitable protective and drainage system.
Why use it?
Because it is elastomeric and bonds to damp concrete without a primer, it seals structures against water ingress while accommodating minor substrate movement and bridging fine cracks, and it adds protection against carbonation and chloride/CO2 ingress under EN 1504-2.
How is it applied?
Pre-dampen the prepared substrate, mix the powder into the liquid with a slow-speed paddle, then apply by stiff brush, roller or trowel - typically two coats of 500 microns to build a 1 mm membrane. Where long-term sun exposure is expected, overcoat with a UV topcoat.
Key advantages
- Elastomeric, polymer-modified film accommodates minor substrate movement and bridges fine shrinkage cracks rather than cracking with the concrete
- Can be applied to damp substrates and requires no primer on normal concrete, saving a process step and suiting humid site conditions
- Factory pre-blended two-component readymix kit gives consistent quality and removes site-batching error
- Seamless, fully bonded membrane with no laps or joints - no welding, torching or adhesives as with sheet systems
- Bonds tenaciously to concrete (1.6 MPa pull-off, EN 1542) so leaks cannot track laterally between membrane and substrate
- Classified under EN 1504-2 for ingress protection, moisture control and increased resistivity, adding carbonation and CO2 resistance to concrete
- Applied by stiff brush, roller or trowel, so it follows complex geometry and detail that rigid boards or sheets cannot
- WRAS-approved (grey grade) for contact with potable water, suiting water tanks and reservoirs
Specifications
- Product type: Two-component polymer-modified elastomeric cementitious waterproofing membrane
- Components: Powder (cements, graded aggregates, additives) + liquid polymer component, site-mixed
- Tensile strength: 2.63 N/mm2 (ASTM D412-91)
- Elongation at break: 43% (ASTM D412-91)
- Crack bridging: Passed (ASTM C836)
- Low temperature flexibility: Passed (ASTM C765:1993)
- Water permeability: Nil (DIN 1048 Pt 5:1991)
- Adhesion (pull-off): 1.6 MPa (EN 1542:1999)
- Setting time (foot traffic): 4 hrs + 1 hr on clean dry concrete with adequate airflow at 20-25C
- Standards: EN 1504-2 methods 1.3, 2.2, 5.1, 8.2; WRAS approved (grey grade)
- Application: Stiff brush, roller or trowel; typically 2 coats of 500 microns = 1 mm total
- Coverage / yield: approx. 14.5 m2 per pack at 1 mm thick (theoretical)
- Supply: Readymix kit - 15 kg powder + 10 kg liquid (per UK TDS)
- Substrate / primer: Applied to damp substrate; no primer required on normal concrete
- UV exposure: Overcoat with Nitoproof UVR Topcoat for long-term direct sunlight
- Temperature / shelf life: Apply 3C (rising) to 40C; 12 months in original sealed containers
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About Fosroc Brushbond FLXIII
A plain-language overview of what Fosroc Brushbond FLXIII is, the problem it solves and how Space Arc Engineering positions it in a specification.
Fosroc Brushbond FLXIII is a two-component, polymer-modified elastomeric waterproofing membrane for concrete and masonry surfaces. It is supplied as a readymix kit: a powder component of specially selected cements, graded hard-wearing aggregates and additives, blended on site with a liquid polymer component. Once mixed it forms an easily brushable coating that is applied to the required thickness and cures to a seamless, flexible membrane.
Unlike a rigid cementitious slurry, the polymer modification gives Brushbond FLXIII genuine elastomeric behaviour, so the cured film tolerates the minor movement and fine cracking that concrete undergoes in service. A standout practical advantage is that it can be applied directly to damp substrates and needs no separate primer on normal concrete, which suits the realities of Indian site conditions where surfaces are rarely bone-dry. The factory pre-blended two-component system also removes the guesswork of site batching and gives consistent quality from kit to kit.
Space Arc Engineering supplies Brushbond FLXIII and supports specifiers and contractors with substrate assessment, detailing and trained application. It is a membrane for water-retaining and water-excluding concrete structures - buried walls, basements, water tanks, sumps and reinforced-concrete roof decks - rather than a decorative or self-finished exposed coating. Because regional Fosroc datasheets and grades can differ, we always supply the current Technical Data Sheet against your specific project before finalising a specification.
The technical insight
Why Fosroc Brushbond FLXIII behaves the way it does — the mechanism behind the performance, in specifier-friendly terms.
Brushbond FLXIII works on the principle of polymer-modified cement chemistry: the liquid polymer disperses through the fresh cement matrix and, as the cement hydrates, the polymer coalesces into a continuous flexible phase that interpenetrates the hardened paste. This polymer phase is what converts a normally brittle cementitious coating into an elastomeric membrane - per the Fosroc TDS the cured film records about 43% elongation at break and 2.63 N/mm2 tensile strength (ASTM D412-91), passes crack bridging to ASTM C836 and low-temperature flexibility to ASTM C765, and develops a pull-off adhesion of 1.6 MPa to concrete (EN 1542). The membrane is classified under EN 1504-2 surface protection methods 1.3 (ingress protection), 2.2 (moisture control), 5.1 (physical resistance) and 8.2 (increasing resistivity), and is WRAS-approved in the grey grade for contact with potable water.
Where Fosroc Brushbond FLXIII is used
Typical applications Fosroc Brushbond FLXIII is specified for, supplied by Space Arc Engineering across Delhi NCR, Ghaziabad, Noida and Uttar Pradesh.
- Waterproofing of buried concrete structures - bridge abutments, culverts and retaining walls
- Basement and below-grade wall and slab waterproofing against ground water
- Non-trafficked reinforced-concrete roof decks (with protective and drainage system)
- Internal lining of water tanks, reservoirs and sumps (grey WRAS-approved grade for potable water)
- Protection of concrete against carbonation, CO2 and chloride-driven ingress (EN 1504-2)
- Waterproofing of wet-area concrete substrates beneath screeds, tiles or protective finishes
- Masonry and gypsum-board surfaces (porous boards first sealed with Nitobond AR)
Key advantages
The properties that make Fosroc Brushbond FLXIII the right choice — drawn from the manufacturer's product literature.
- Elastomeric, polymer-modified film accommodates minor substrate movement and bridges fine shrinkage cracks rather than cracking with the concrete
- Can be applied to damp substrates and requires no primer on normal concrete, saving a process step and suiting humid site conditions
- Factory pre-blended two-component readymix kit gives consistent quality and removes site-batching error
- Seamless, fully bonded membrane with no laps or joints - no welding, torching or adhesives as with sheet systems
- Bonds tenaciously to concrete (1.6 MPa pull-off, EN 1542) so leaks cannot track laterally between membrane and substrate
- Classified under EN 1504-2 for ingress protection, moisture control and increased resistivity, adding carbonation and CO2 resistance to concrete
- Applied by stiff brush, roller or trowel, so it follows complex geometry and detail that rigid boards or sheets cannot
- WRAS-approved (grey grade) for contact with potable water, suiting water tanks and reservoirs
Limitations & considerations
Where Fosroc Brushbond FLXIII is not the right answer. Check these constraints from the manufacturer before specifying — using it outside its scope is the most common cause of failure.
- Not inherently UV-stable for permanent sun exposure - the TDS requires overcoating with Fosroc Nitoproof UVR Topcoat where long-term direct sunlight is expected, so it is not a finished exposed terrace coating on its own
- It is a non-trafficked / light-foot-traffic membrane: it takes only occasional foot traffic when cured and is not a wearing surface, so trafficked decks, podiums and terraces need a protective screed, tiles or separate wearing course over it
- It is a cementitious membrane for concrete and masonry; it is not formulated for flexible or movement-prone substrates such as timber sub-floors, and porous boards (e.g. gypsum) must first be sealed with Fosroc Nitobond AR
- Elongation (about 43%) and crack-bridging are suited to fine cracks - it is not a high-movement joint or expansion-joint solution; active or wide cracks need dedicated crack treatment or a joint system
- Application is temperature-sensitive: do not apply above 40C substrate/air or below 3C and rising, and avoid freezing conditions for 24 hours after application
Selection & best practice
How to decide whether Fosroc Brushbond FLXIII fits your job — and how to apply it so the repair lasts.
Specify Brushbond FLXIII where you need a fully bonded, seamless, flexible waterproof membrane on concrete or masonry that will be buried or protected - basements, retaining walls, bridge abutments, culverts, water tanks and non-trafficked RC roof decks under a finish. Choose it over rigid crystalline or plain cementitious coatings when minor movement or fine cracking is expected, and over sheet/torch-applied membranes when complex detailing, damp substrates or potable-water contact (grey grade) are decisive. Where the surface will be permanently exposed to sun, walked on, or is a timber/wet-area floor, pair it with the correct topcoat or protection - or select a Fosroc product positioned for that exposure - rather than relying on FLXIII alone.
Application best practice
- Prepare the substrate to sound, clean concrete free of oil, grease, laitance and dust; cut out spalled or disintegrated concrete and reinstate with the Fosroc Renderoc system before membrane application
- Pre-dampen the substrate to a uniformly 'just visibly damp' condition, sponge off any excess and stop running water with a plugging mortar such as Renderoc Plug before coating
- Mix correctly: place about two-thirds of the liquid in the container, add the powder gradually under slow-speed (350-450 rpm) paddle mixing for 3-4 minutes, then add the remaining liquid and mix a further 1-2 minutes; use within pot life
- Apply two coats of about 500 microns each to build the recommended 1 mm membrane, allowing the first coat to set before the second; reinforce corners, fillets and junctions as detailed
- Treat coverage as theoretical - the kit yields about 14.5 m2 per pack at 1 mm, but allow for wastage and substrate texture when ordering
- Where long-term sun exposure applies, overcoat with Nitoproof UVR Topcoat; on potable-water structures use the grey WRAS-approved grade, and protect trafficked areas with a screed or tiles
Specifications
Indicative properties from the manufacturer's literature. Always confirm batch-specific values against the current TDS before specification.
| Product type | Two-component polymer-modified elastomeric cementitious waterproofing membrane |
|---|---|
| Components | Powder (cements, graded aggregates, additives) + liquid polymer component, site-mixed |
| Tensile strength | 2.63 N/mm2 (ASTM D412-91) |
| Elongation at break | 43% (ASTM D412-91) |
| Crack bridging | Passed (ASTM C836) |
| Low temperature flexibility | Passed (ASTM C765:1993) |
| Water permeability | Nil (DIN 1048 Pt 5:1991) |
| Adhesion (pull-off) | 1.6 MPa (EN 1542:1999) |
| Setting time (foot traffic) | 4 hrs + 1 hr on clean dry concrete with adequate airflow at 20-25C |
| Standards | EN 1504-2 methods 1.3, 2.2, 5.1, 8.2; WRAS approved (grey grade) |
| Application | Stiff brush, roller or trowel; typically 2 coats of 500 microns = 1 mm total |
| Coverage / yield | approx. 14.5 m2 per pack at 1 mm thick (theoretical) |
| Supply | Readymix kit - 15 kg powder + 10 kg liquid (per UK TDS) |
| Substrate / primer | Applied to damp substrate; no primer required on normal concrete |
| UV exposure | Overcoat with Nitoproof UVR Topcoat for long-term direct sunlight |
| Temperature / shelf life | Apply 3C (rising) to 40C; 12 months in original sealed containers |
Coverage, dosage, pack sizes and cure times vary with substrate and conditions — request the full TDS for certified technical data.
Industry use cases
Real-world scenarios where Fosroc Brushbond FLXIII is the practical choice — the teams who reach for it and the jobs it does for them.
- Infrastructure: waterproofing bridge abutments, box culverts and earth-retaining structures before backfill
- Water and wastewater: lining RCC water tanks, overhead/underground reservoirs and treatment-plant structures
- Buildings: basement raft and retaining-wall tanking, lift-pit and sump waterproofing in commercial and residential projects
- Roofing: waterproofing non-trafficked RC roof decks and inverted/buried roofs under insulation, screed or green-roof build-ups
- Concrete durability/repair: surface protection of RC elements against carbonation and moisture as part of a Renderoc repair scheme
Frequently asked questions
Common questions about specifying and sourcing Fosroc Brushbond FLXIII.
What is Fosroc Brushbond FLXIII?
It is a two-component, polymer-modified elastomeric waterproofing membrane for concrete and masonry. A factory-blended powder of cements, graded aggregates and additives is mixed on site with a liquid polymer component to form a brushable slurry that cures to a seamless, flexible waterproof coating.
Is 'Brushbond Flex' the same product?
Fosroc does not market a product called 'Brushbond Flex'. The correct product in the Brushbond range is Brushbond FLXIII (FLX = flex), the two-component polymer-modified elastomeric membrane described here. Other Brushbond variants (such as UltraFlex, RFX or Roofguard) are positioned for different exposures, so always confirm the exact grade against the project TDS.
Where should Brushbond FLXIII be used - and where not?
It is designed for buried structures (abutments, culverts, retaining walls, basements), water tanks and non-trafficked RC roof decks under a protective finish. It is not an exposed wearing surface: trafficked decks need protection over it, and permanent sun exposure needs a UV topcoat. It is a cementitious membrane for concrete/masonry, not for timber sub-floors.
Does Brushbond FLXIII need a primer, and can it go on damp concrete?
On normal concrete no separate primer is required, and the membrane can be applied to a damp (pre-wetted, not running-wet) substrate. The exception is porous boards such as gypsum, which should first be sealed with Fosroc Nitobond AR before coating.
Is Brushbond FLXIII UV-resistant and walkable?
Not for permanent service on its own. The TDS calls for overcoating with Nitoproof UVR Topcoat where long-term direct sunlight is expected, and the membrane only takes occasional foot traffic when cured - trafficked areas need a screed, tiles or other protective wearing course over the membrane.
How much crack movement can it bridge?
Brushbond FLXIII is elastomeric (about 43% elongation at break, ASTM D412-91) and passes crack bridging to ASTM C836, so it bridges fine shrinkage cracks. It is not a high-movement or expansion-joint solution; active or wide cracks need dedicated crack/joint treatment before the membrane.
What is the coverage and pack size?
Per the Fosroc UK TDS the kit is supplied as 15 kg powder plus 10 kg liquid and yields about 14.5 m2 per pack at 1 mm thickness (two 500-micron coats). Coverage is theoretical - allow for wastage and substrate texture. Regional Fosroc datasheets can vary, so request the current TDS from Space Arc for your project.
References
Manufacturer and technical sources this page draws on. Always confirm current data against the live TDS before specification.
Source Fosroc Brushbond FLXIII for your project
Space Arc Engineering is an authorised distributor for Fosroc, serving Delhi NCR, Ghaziabad, Noida and Uttar Pradesh. Talk to us for pricing, the technical data sheet and on-site support.
Or email info@space-arc.com · www.space-arc.com