About Sika Sikalastic-11 Primer W

Sikalastic-11 Primer W is the primer Sika pairs with its Sikalastic range of liquid-applied roof membranes, and its whole job is to solve the single biggest cause of membrane failure on Indian rooftops: poor adhesion to the substrate. Sold as a pre-batched 5 kg set (1 kg Part A resin plus 4 kg Part B hardener), it is a genuinely water-based, low-VOC epoxy that mixes into a thin white liquid of about 1.2 kg/L. Because the formulation is low in viscosity, it wets out and penetrates the surface rather than sitting on top, which is exactly what you want when the deck below is thirsty concrete, an old cement screed or a chalky brick parapet. The product was formerly sold as Lanko Flowprime WB, so specifiers who know that legacy name are looking at the same material under Sika branding.\n\nWhat makes it a workhorse on refurbishment jobs is how many surfaces it will accept. The same tin primes concrete, cement screeds and epoxy mortars, stabilises high-absorbency substrates such as brick and asbestos sheeting, and-when followed by a quartz-sand broadcast-keys onto metal roof sheets and bitumen felt as well. That versatility matters in the field, where a single terrace can carry three or four different substrates in one waterproofing scope. Because it is water-based, site teams avoid the strong solvent odour and flammability that comes with solvent primers, which is a real advantage on occupied buildings, enclosed plant rooms and hospitals where ventilation and fumes are a live concern.

The technical insight

The performance of any liquid-applied membrane is only as good as the bond at the interface, and that is precisely where a penetrating primer earns its place. Sikalastic-11 Primer W is deliberately formulated at low viscosity so the mixed epoxy is drawn into surface pores and micro-cracks by capillary action instead of bridging over them. As the epoxy cures inside those voids, it locks together the loose surface laitance and dust that plague old concrete and screeds, converting a weak, friable top layer into a sound, consolidated one. The result is a mechanical key plus a chemical tie: the cured primer film presents an epoxy-compatible surface that the subsequent Sikalastic membrane can bond to reliably. On non-porous or slick substrates such as metal and bitumen, penetration alone is not enough, so a quartz-sand broadcast into the wet primer creates a rough, high-surface-area profile that gives the membrane something physical to grip. The under-6% substrate moisture limit and the dew-point rule are not fine print-they exist because trapped moisture or condensation at the interface is what later drives blistering and disbondment, so controlling them at priming stage is what buys the whole system its service life.

Where it is used

• Priming concrete roof decks, cement screeds and epoxy mortar surfaces before Sikalastic liquid membrane application
• Sealing and stabilising high-absorbency substrates such as brickwork, parapets and asbestos-cement roof sheets
• Priming metal roof sheeting and profiled decking, followed immediately by a quartz-sand broadcast
• Priming aged bituminous felt and bitumen coatings ahead of overcoating, again with sand broadcast
• Consolidating dusty or friable cementitious substrates on refurbishment and re-waterproofing jobs
• Bonding coat under Sikalastic liquid-applied roof membranes on commercial and industrial rooftops
• Terrace and podium waterproofing preparation over mixed-substrate decks
• Priming timber and timber-based panel roof decks that are sound and firmly fixed

Key advantages

• Water-based and low-VOC, so it is far more tolerable than solvent primers on occupied buildings, hospitals and enclosed roof plant
• Low viscosity gives strong penetration into porous concrete, screed and brick for a deep mechanical key
• Genuinely multi-substrate: one product for concrete, screed, brick, asbestos, metal, wood and bitumen
• Stabilises and consolidates weak, dusty cementitious surfaces that would otherwise fail the membrane bond
• Short waiting time to overcoating of roughly 2-4 hours keeps priming and membrane work on the same day
• Pre-batched 1:4 kit removes site dosing guesswork and the errors that come with field-measured two-part systems
• Purpose-matched to the Sikalastic membrane range, so the primer and topcoat are a warranted system rather than a mix-and-match
• Non-flammable water base reduces the fire-safety and storage precautions needed with solvent-based primers

Limitations & considerations

• It is a primer only, not a waterproofing layer, and must always be overcoated with a Sikalastic liquid membrane
• Application is restricted to a narrow +5 C to +30 C window for both air and substrate, ruling out peak-summer midday work on exposed decks
• Substrate moisture must be under 6% by weight and free of standing water, which is demanding during and just after the monsoon
• Pot life is only about 25 minutes at 25 C and its end gives no visible warning, so mixed material must be used quickly or discarded
• Metal and bitumen substrates require an immediate quartz-sand broadcast, adding a material and a step to the sequence
• For heavy-duty industrial floor coatings or damp-tolerant priming a dedicated floor or solvent-based epoxy primer may be more appropriate

Selection & best practice

Specifications

Industry use cases

How we position Sika Sikalastic-11 Primer W

Sikalastic-11 Primer W is a system component, not a standalone product-specify it whenever you are laying a Sika liquid membrane such as Sikalastic-560, Sikalastic-490 or the Sikalastic-618 range, where priming with the matched primer keeps the whole build-up under one warranted system. For substrate stabilisation and construction-joint detailing on the same roof, pair it with Sikaflex or SikaTop repair products from the Sika family. Where the specification calls for the Fosroc system instead, the genuine like-for-like counterpart is Fosroc Nitoproof WB Primer-also a low-VOC, water-based epoxy primer for liquid-applied waterproofing membranes on concrete. As an authorised distributor for both Sika and Fosroc, Space Arc can supply either primer to match whichever membrane system the consultant has approved, and can advise where a solvent-based or damp-tolerant primer would serve better on a difficult deck.

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