Fosroc Brushbond FLXIII
Two-component polymer-modified cementitious slurry that cures into a seamless, crack-bridging elastomeric membrane — brush, roller or trowel applied to concrete and masonry, no primer needed.
What is it?
A two-part flexible waterproofing coating: 15 kg of factory-blended cementitious powder mixed on site with 10 kg of liquid polymer to form a brushable elastomeric slurry.
Where is it used?
Basements, retaining walls and buried structures, water tanks and sumps, non-trafficked RC roof decks, and sunken wet areas beneath screeds.
Why use it?
43% elongation bridges hairline cracks, it bonds to damp concrete at 1.6 MPa without primer, and it carries EN 1504-2 compliance with WRAS approval on the grey grade.
How is it applied?
Pre-dampen the prepared substrate, mix powder into liquid with a slow-speed drill, then apply two coats of 500 microns each to build a 1 mm membrane.
About Fosroc Brushbond FLXIII
Brushbond FLXIII — written into many Indian BOQs simply as Brushbond Flex — is Fosroc’s workhorse flexible cementitious waterproofing membrane. Each kit pairs 15 kg of factory-blended powder (selected cements, graded hard-wearing aggregates and additives) with 10 kg of liquid polymer. Mixed on site, the two components produce an easily brushable slurry that cures into a seamless elastomeric film, typically built to 1 mm over two coats and bonded directly to concrete or masonry with no separate primer.
For specifiers, the appeal is the certification trail as much as the numbers. The product is CE-marked to EN 1504-2 for ingress protection, moisture control, physical resistance and increasing resistivity, and the grey grade holds WRAS approval for contact with potable water. Space Arc Engineering supplies Brushbond FLXIII from authorised Fosroc channel stock across Delhi NCR and pan-India, with trained applicator crews available where a warranted, supervised installation is required.
The technical insight
The membrane’s behaviour comes from what happens during cure. As the cement fraction hydrates, the dispersed polymer coalesces into a continuous elastic film threaded through the cementitious matrix — cement contributes adhesion and alkalinity, polymer contributes stretch. The cured film tests at 2.63 N/mm² tensile strength with 43% elongation at break (ASTM D412) and passes ASTM C836 crack bridging, so it accommodates the hairline shrinkage and thermal cracking that fractures rigid slurry coatings. Because the chemistry is cement-compatible, damp substrates help rather than hinder: pull-off adhesion is 1.6 MPa (EN 1542) on pre-wetted concrete. Diffusion data tells the second story — an equivalent air layer thickness (Sd) of 107 m against CO₂ makes it a genuine anti-carbonation coating, while water permeability is nil under DIN 1048 Part 5 pressure testing.
Where it is used
- Basement rafts, walls and lift pits in high-water-table areas
- Buried infrastructure — bridge abutments, culverts, retaining walls and foundations
- Non-trafficked RC roof decks, used with a protective screed or drainage layer
- Water tanks, reservoirs and sumps — WRAS-approved grey grade for potable contact
- Sunken slabs, bathrooms and balconies as a thin bonded membrane beneath screeds
- Anti-carbonation and chloride-ingress protection on exposed structural concrete
- Complex details — pipe penetrations, upstands, corners and junctions where sheet membranes cannot conform
Key advantages
- Applies to damp (pre-wetted) substrates — no waiting for bone-dry concrete and no primer on normal concrete
- 43% elongation with passed ASTM C836 crack bridging tolerates hairline substrate movement
- Seamless and fully bonded at 1.6 MPa pull-off — no laps or joints, and no lateral water tracking under the membrane
- Factory pre-blended kit removes site-batching error and keeps quality consistent between crews
- EN 1504-2 (methods 1.3, 2.2, 5.1, 8.2) compliance plus WRAS approval simplify specification sign-off
- Doubles as an anti-carbonation coating (CO₂ Sd 107 m), protecting rebar in the same pass
- Accepts foot traffic in roughly 4 hours at 20–25°C and occasional foot traffic once cured
Limitations & considerations
- Not UV-stable long term — permanently exposed areas must be overcoated with Nitoproof UVR Topcoat or covered with a protective screed
- Not a wearing surface — trafficked decks and tiled areas need a protective screed over the membrane
- Application window is 3°C (and rising) to 40°C; freezing must be avoided for 24 hours after application, and high heat can cause colour-shade variation
- Bridges fine, dormant cracks only — live cracks and movement joints need a dedicated joint sealant or treatment
- Active water ingress must first be stopped with a plugging mortar (e.g. Renderoc Plug 20), and porous boards such as gypsum need sealing with Nitobond AR
Selection & best practice
Get the substrate right first: remove oil, grease, laitance and loose material, and reinstate spalled concrete with the Renderoc system. Dampen the surface until just visibly moist — sponge off any standing water. Mix by adding the powder gradually into about two-thirds of the liquid using a slow-speed drill (350–450 rpm) with a mixing paddle, blend 3–4 minutes until lump-free, then add the remaining liquid and mix a further 1–2 minutes. Apply with a stiff 120–200 mm brush like a paint: two coats of 500 microns each, the second coat at right angles to the first, for a 1 mm membrane. Clean tools with water immediately; protect the fresh coating from rain, frost and early trafficking.
Specifications
| Supply (per kit) | 15 kg powder + 10 kg liquid (14.5 litres yield) |
| Coverage | 14.5 m² per pack at 1 mm thickness (2 coats of 500 microns); theoretical |
| Tensile strength | 2.63 N/mm² (ASTM D412-91) |
| Elongation at break | 43% (ASTM D412-91) |
| Adhesion (pull-off) | 1.6 MPa (EN 1542:1999) |
| Water permeability | Nil (DIN 1048 Part 5:1991) |
| Setting time, foot traffic | 4 hours ± 1 hour at 20–25°C on dry concrete |
| Application temperature | +3°C (rising) to 40°C |
| Shelf life | 12 months in unopened containers, dry storage (reduced in high heat/humidity) |
Industry use cases
Residential & Commercial Basements
Internal negative-side or external positive-side coating on rafts and retaining walls in Delhi NCR’s high-water-table pockets, bonded so leaks cannot track laterally.
Infrastructure
Buried protection for bridge abutments, culverts and metro structures — damp-tolerant application suits freshly struck concrete on fast-moving programmes.
Water & Wastewater
Lining for OHTs, UGTs, STP/WTP tanks and sumps; the WRAS-approved grey grade covers potable-water contact for municipal and building supplies.
Industrial & Institutional Roofs
Waterproofing of non-trafficked RC decks under a protective screed or drainage layer, with anti-carbonation protection thrown in.
High-Rise Wet Areas
Thin bonded membrane in bathrooms, balconies and sunken portions before screed and tile, where sheet systems are impractical around penetrations.
Frequently asked questions
Is Brushbond Flex the same as Brushbond FLXIII?
What area does one kit cover?
Can it be used inside drinking-water tanks?
Does the concrete need to be dry, and is a primer required?
Can I leave it exposed on a roof?
Can I tile or screed over it?
How we position Fosroc Brushbond FLXIII
Brushbond FLXIII sits in the middle of Fosroc’s waterproofing range: it is the economical, damp-tolerant choice for buried, tanked and protected areas. Where a roof stays permanently exposed or movement is higher, step up to Fosroc Nitoproof 600 liquid polyurethane, or pair FLXIII with Nitoproof UVR Topcoat for UV protection. Preparation partners come from the same family — Renderoc Plug 20 for live leaks, the Renderoc repair range for spalled concrete, and Nitobond AR for porous boards. Space Arc also stocks comparable two-component acrylic-cementitious coatings from Dr. Fixit and Sika where a project specification names those systems.
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