Dr. Fixit FlexiPU 500GC
A single-component, moisture-cured PU/polyurea membrane built to go onto damp, green concrete — seamless, primerless, and rated for real hydrostatic pressure.
What is it?
A single-component, liquid-applied, moisture-triggered modified urethane/polyurea elastomeric membrane, coal-tar free, black in colour, meeting ASTM C836, supplied ready-to-use in an 18.9-litre (22.5 kg) drum.
Where is it used?
Unconfined retaining walls, podium decks, roof and terrace slabs under screed, planter and landscape areas, and any vertical or horizontal RCC surface that is still damp or freshly de-shuttered.
Why use it?
Because it cures using the substrate’s own residual moisture instead of fighting it — waterproofing can start roughly 24 hours after casting, without a primer, and still deliver root resistance, dynamic crack bridging and resistance up to 7 bar of hydrostatic head.
How is it applied?
Stirred mechanically (no mixing ratio to get wrong), then rolled, squeegeed or airless-sprayed in two perpendicular coats with 225 gsm chopped glass fiber strand embedded wet-in-wet, and protected within 48 hours to 10 days with a screed or protection board.
About Dr. Fixit FlexiPU 500GC
On a live Delhi NCR site, the concrete rarely waits for the waterproofing schedule — podium slabs get de-shuttered, retaining walls get backfilled against, and terraces need a screed on top well before the standard 28-day cure window is anywhere close. Most single-component PU membranes are built for that dry, cured substrate and will blister or fish-eye on anything damper. Dr. Fixit FlexiPU 500GC flips that constraint: its moisture-triggered modified urethane/polyurea chemistry uses the water still locked in green concrete as part of the cure trigger, so it is formulated to go onto surfaces as early as 24 hours after casting or de-shuttering, on both vertical and horizontal RCC.
It ships as a single, ready-to-use, coal-tar-free black liquid in an 18.9-litre drum — no second component, no pot-life clock, and per the manufacturer’s data no primer needed on properly prepared concrete. Applied in two coats reinforced wet-in-wet with 225 gsm chopped glass fiber strand, it builds to a 1.5 mm dry film that stretches roughly 450% before it lets go and still holds a genuine 7 bar of hydrostatic head — which is what puts it in the same conversation as podium decks and unconfined retaining walls rather than just terrace damp-proofing. Root resistance to CEN/TS 14416 makes it a sensible pick under planters and landscape decks too.
The technical insight
The chemistry worth understanding here is the word “moisture-triggered.” Conventional single-component polyurethane coatings cure by pulling ambient humidity in from the top surface downward — which is exactly why they are specified for cured, dry concrete: moisture coming up from below traps solvent, causes pinholing, or simply will not let the film set. FlexiPU 500GC’s modified urethane/polyurea formulation is engineered the other way — it reacts with moisture already present in green or damp concrete as part of its own cure path, which is why the data sheet permits application just 24 hours after de-shuttering and even allows adding 2.5-5% water by volume to speed curing in cold or dry weather. The mechanical numbers tell the reinforcement story: plain-film tensile strength is a modest 2.0 N/mm², but embedding the 225 gsm chopped glass fiber strand mid-coat lifts that to 7.0 N/mm² and tear resistance to 60 N/mm — the strand is doing real structural work, not just marketing. Surface prep still matters: the sheet calls for a mechanically achieved CSP 3 profile, and cracks over 1 mm need a strip coat of chopped fiber over Dr. Fixit PU Sealant before the main membrane goes on.
Where it is used
- Podium decks over habitable basements, ahead of the landscape screed
- Unconfined (exposed-face) retaining walls below grade
- Terrace and roof slabs, applied straight after de-shuttering and protected under a screed
- Planter boxes and landscape/podium areas needing root-resistant waterproofing
- Balcony and sunken-slab waterproofing before floor screed
- Wet areas and damp substrates where a 28-day dry-out isn’t practical on site
- Newly repaired or patch-concreted areas that need waterproofing without a long drying wait
- Below-grade structural walls under genuine hydrostatic pressure (non-potable, non-water-retaining)
Key advantages
- Cures on damp, green concrete — application can start about 24 hours after casting or de-shuttering instead of waiting out a 28-day dry period
- Genuinely primerless on properly prepared (CSP 3) concrete, saving a working day and a line item
- Single component straight from the drum — no mixing ratio, no pot-life panic on a hot afternoon
- 225 gsm chopped glass fiber reinforcement lifts tensile strength from 2.0 to 7.0 N/mm² and tear resistance to 60 N/mm
- Root resistant to CEN/TS 14416 — safe to run under planters and landscape decks
- Rated to 7 bar hydrostatic head (ASTM D5385), genuine below-grade retaining-wall performance rather than splash-zone damp-proofing
- Dynamic crack bridging (EN 1062-7, Class B4.2) with roughly 450% elongation, so it moves with hairline cracking instead of splitting
- Coal-tar free — none of the odour or handling baggage of the older bituminous PU systems it is replacing on site
Limitations & considerations
- Not for permanently water-retaining structures such as tanks or STPs — the manufacturer excludes this use outright
- Needs UV protection fast: horizontal applications must get a geotextile-and-screed layer within 10 days, vertical ones a protection board within 48 hours — it isn’t a stand-alone exposed roof coating for the long term
- Can’t be applied over standing or flowing water, or over an existing coating or curing compound — surface prep has to be genuine, not cosmetic
- Supplied only in black — it needs a topping screed, tiling or protection board for anything that will be walked on or seen
- Full cure is rated at 7 days at 24°C, so screed-laying, backfilling and other follow-on trades have to respect the sequencing, not just the 48-hour minimum recoat window
- Hitting the rated tensile and tear figures depends on correct technique — wet-in-wet glass fiber lay-in and the specified coat-wise coverage — so it is an applicator-trained job, not a DIY brush-on
Selection & best practice
Prepare the concrete mechanically to a CSP 3 profile and confirm it is genuinely sound before starting — FlexiPU 500GC is primerless but not surface-prep-free. Treat any crack wider than 1 mm with a strip coat of chopped glass fiber over Dr. Fixit PU Sealant before the main membrane goes on. Stir the material mechanically at slow speed to avoid air entrainment, then apply two coats at right angles to each other, laying the 225 gsm chopped glass fiber strand into the first coat while it is still wet and rolling it flat to avoid wrinkles. In cold or low-humidity conditions, add 2.5-5% water by volume to keep the cure on schedule. Protect the finished membrane promptly — geotextile and screed within 10 days on decks, a protection board within 48 hours on retaining walls — rather than leaving it exposed.
Specifications
| Chemistry | Single-component, moisture-triggered, modified urethane/polyurea (coal-tar free) |
| Standard compliance | ASTM C836 |
| Specific gravity (27±2°C) | 1.18 ± 0.3 g/cc (IS 101) |
| Tensile strength | 2.0 N/mm² plain film; 7.0 N/mm² with 225 gsm glass fiber strand (ASTM D412) |
| Elongation at break (plain film) | 450 ± 50% (ASTM D412) |
| Shore A hardness | 30 (ASTM D2240) |
| Hydrostatic head resistance | Up to 7 bar, pass (ASTM D5385) |
| Theoretical coverage | 1.4-1.45 kg/m² for 1.5 mm DFT in 2 coats |
| Packaging | 18.9 litre (22.5 kg) drum |
Industry use cases
Residential podium / gated community
Waterproofing an unconfined retaining wall and podium deck on a Gurugram basement-plus-podium project where the excavation-to-backfill schedule didn’t allow the usual 28-day concrete dry-out.
High-rise terrace waterproofing
Applying the membrane straight after de-shuttering a freshly cast roof slab so the IPS/tile screed could follow within the same fortnight instead of waiting out a full cure cycle.
Landscape and clubhouse decks
Waterproofing planter boxes and podium landscaping in a gated community, where root resistance mattered as much as waterproofing itself because of deep-rooted ornamental plantings.
Balcony and sunken-slab waterproofing
Treating sunken bathroom and balcony slabs before the floor screed in an individual bungalow, where the primerless, damp-tolerant system avoided a scheduling clash with the plumber.
Repair and retrofit
Waterproofing a patch-repaired retaining wall section where the new concrete couldn’t realistically be left to dry for a month before the site needed it watertight.
Frequently asked questions
Can FlexiPU 500GC really be applied on wet or freshly cast concrete?
Do I need to apply a primer first?
Can I use it inside an overhead or underground water tank?
How much coverage do I get from one drum?
Does it bridge existing cracks in the slab or wall?
Once applied, does it need to be covered up, or can it stay exposed?
How we position Dr. Fixit FlexiPU 500GC
Within the Dr. Fixit range, FlexiPU 500GC sits alongside Dr. Fixit Roofseal and Dr. Fixit Aquashield PU as the brand’s PU-chemistry answers to terrace and general waterproofing, while Dr. Fixit Bathseal covers smaller wet-area jobs and Dr. Fixit Pidicrete URP handles the protective screed or topping that often goes over a membrane like this one on a podium deck. Where a project has already standardised on Fosroc systems, or a specifier wants a pitch-modified single-component PU membrane pitched specifically at below-grade and concealed concrete rather than an exposed roof-and-podium system, Fosroc Nitoproof 600 is the genuine equivalent worth comparing line items against — both are moisture-cured, primer-light PU membranes, and the choice usually comes down to brand standardisation on site and the exact substrate condition rather than a real performance gap.
Fosroc Nitoproof 600 — Where a project has already standardised on Fosroc systems, or a specifier wants a pitch-modified single-component PU membrane pitched specifically at below-grade and concealed concrete rather than an exposed roof-and-podium system, Fosroc Nitoproof 600 is the genuine equivalent worth comparing against.
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