Sika SikaProof A+
A fully bonded FPO pre-applied membrane that locks to the structural concrete, stopping water tracking behind the sheet on blindside basements and deep below-ground works.
What is it?
A flexible polyolefin (FPO) sheet membrane with a hybrid bonding layer, installed before the concrete is poured so it forms a permanent, integral bond with the structural slab or wall.
Where is it used?
Basement rafts and retaining walls cast against soil or piling, lift pits, cut-and-cover boxes, tunnels and other below-ground reinforced concrete where the outer face is inaccessible after casting.
Why use it?
The full bond to concrete means that even if the sheet is punctured, water cannot migrate laterally between membrane and structure, so a leak stays local and traceable instead of travelling.
How is it applied?
Rolled out grid-side up over blinding or fixed to formwork/shuttering, laps sealed with SikaProof tapes, then reinforcement is fixed and concrete cast directly onto it.
About Sika SikaProof A+
SikaProof A+ belongs to Sika’s pre-applied, fully bonded waterproofing family, built on the same FPO (flexible polyolefin) chemistry Sika has proven in tunnel lining membranes for decades. The sheet is laid out before any concrete is placed, with its bonding grid facing the wet mix. As the concrete hydrates it keys mechanically and chemically into that grid, so the finished membrane behaves as one continuous skin married to the structure rather than a loose sheet draped behind it. This is the defining difference from conventional loose-laid tanking, and it is exactly what a blindside basement needs, where you can never get back to the outer face to chase a leak.
For Indian projects the product is offered in two grades so the specification can match the exposure and the ground conditions. SikaProof A+ 08 uses a 0.8 mm membrane and suits typical basement and below-ground work; SikaProof A+ 12 steps up to a 1.2 mm membrane for deeper structures, higher water heads and more aggressive ground. Both are supplied in rolls of 1.0 m or 2.0 m width by 25 m length, and both run as a system with dedicated SikaProof tapes for laps, penetrations and detailing. Where ground gas is a concern, the system extends with Sikadur-120 LM as a gas-protection layer. As an authorised Sika distributor and applicator across Delhi NCR and Pan-India, Space Arc supplies the membrane, the tapes and the site guidance as one package.
The technical insight
The engineering value sits in the word “bonded”. A loose sheet membrane relies on the sheet staying intact over its whole area, because any breach lets water spread freely in the void behind it until it finds a construction joint or crack to enter the structure, often metres from the puncture. SikaProof A+ removes that void. Its hybrid bonding layer creates a dual bond with the fresh concrete, part adhesive grip and part a polymer-modified cementitious key into the surface grid, so the membrane is fused to the concrete face with no continuous cavity behind it. If a service penetration is drilled carelessly or a stone punctures the sheet, water entering that point has nowhere to travel and shows up directly above the defect, which is what makes remedial injection viable. The FPO carrier itself contributes the other half of the performance: high elongation, so it bridges the shrinkage and settlement cracks that always appear in structural concrete, plus strong resistance to the alkalis, sulphates, natural ground gases and brackish water that attack membranes below the water table.
Where it is used
- Basement raft slabs and retaining walls cast against soil, rock or contiguous piling (blindside waterproofing)
- Lift pits, sump pits and other deep pockets where external access is lost after casting
- Cut-and-cover boxes, underpasses and metro station structures
- Tunnel inverts and buried service or utility tunnels
- Podium and transfer slabs over occupied or below-ground space
- Water-retaining and below-water-table reinforced concrete structures
- Structures on contaminated or gassing ground, in combination with the system gas-protection layer
- Deep foundations, pile caps and tanking to buried plant rooms
Key advantages
- Full, permanent bond to the concrete stops lateral water tracking, so a breach stays local and traceable
- Pre-applied over blinding or against shuttering removes the need for external access after the pour
- High elongation FPO carrier bridges shrinkage and settlement cracks in the structural slab
- Resists ground water, sulphates, alkalis and natural ground gases found below the water table
- Two grades (0.8 mm and 1.2 mm membrane) let the spec match water head and ground aggressiveness
- Complete system of matched tapes seals laps, penetrations and details reliably
- Built on FPO chemistry with a long tunnelling track record for ageing and durability
- Backed by Sika technical support plus local supply and applicator input from Space Arc
Limitations & considerations
- It is a pre-applied system: it must be installed before reinforcement and concrete, so it cannot rehabilitate an existing wet basement from outside
- Needs a sound, reasonably level substrate (blinding or shuttering) free of sharp protrusions to seat correctly
- Lap and detail sealing with the correct SikaProof tapes is critical; poor jointing undermines the bonded principle
- Ground-gas protection is not automatic and needs the additional system layer where gas is present
- As a rolled sheet it favours large continuous areas; heavily congested or intricate geometry needs careful detailing
- Correct membrane orientation (bonding grid toward the fresh concrete) must be maintained throughout the pour
Selection & best practice
Prepare a firm, level substrate first: minimum 7-day cured blinding or clean shuttering, free of standing water, debris and sharp edges. Roll the membrane out with the bonding grid facing the concrete to be cast, keeping sheets taut and flat. Maintain adequate side and end laps and seal every lap, corner and penetration with the matched SikaProof tape system, giving particular attention to pipe entries, construction joints and internal corners, which is where most below-ground failures originate. Protect the laid membrane from foot traffic, rebar chairs and dropped tools before the pour, and inspect and repair any punctures with the system tape before concreting. Place concrete carefully so the membrane is not displaced, and keep work within the +5 degC to +45 degC ambient range. Where the site is gassing, incorporate the gas-protection layer as part of the same continuous envelope.
Specifications
| Product type | Pre-applied, fully bonded FPO (flexible polyolefin) sheet membrane |
| Bonding mechanism | Hybrid bonding layer forming a dual (adhesive + cementitious grid) bond with fresh concrete |
| Grades | SikaProof A+ 08 (0.8 mm membrane) and A+ 12 (1.2 mm membrane) |
| Roll dimensions | 1.00 m or 2.00 m width x 25 m length |
| Tensile strength (A+ 08) | >= 500 N/50 mm, both MD and CMD |
| Elongation at break (A+ 08) | >= 1000% |
| Resistance to impact (A+ 08) | >= 300 mm |
| Watertightness | Pass (Method B, 24 h at 60 kPa) |
| Application temperature | +5 degC to +45 degC ambient air |
Industry use cases
Commercial & IT parks
Deep multi-level basements and car parks cast against piling, where blindside tanking must be right first time because the outer face is buried.
Metro & infrastructure
Cut-and-cover station boxes, underpasses and service tunnels needing a durable, crack-bridging envelope against the water table.
Residential high-rise
Basement rafts, retaining walls and lift pits under towers, where a traceable, non-tracking membrane simplifies any future remedial work.
Industrial & contaminated sites
Below-ground structures on gassing or aggressive ground, combining the bonded membrane with the system gas-protection layer.
Frequently asked questions
What makes SikaProof A+ different from ordinary loose-laid tanking sheets?
Which grade should I specify, A+ 08 or A+ 12?
Can SikaProof A+ fix an existing leaking basement?
Does it protect against ground gases like methane and radon?
What roll sizes are supplied and how are laps sealed?
Is Space Arc an authorised Sika supplier for this product?
How we position Sika SikaProof A+
SikaProof A+ sits at the premium, engineered end of below-ground waterproofing and is best paired with the rest of the Sika basement system: the SikaProof tape range for laps and detailing, Sikadur-120 LM where ground-gas protection is needed, and Sika waterstops or SikaSwell profiles at construction and expansion joints to complete a continuous watertight envelope. For projects standardised on Fosroc, the directly equivalent pre-applied fully bonded membrane is Fosroc Proofex Engage, which some specifiers prefer where the wider Fosroc Proofex tanking and joint system is already the site standard. We stock and apply both families and will recommend the one that best fits your specification, ground conditions and existing approved-vendor list rather than pushing a single brand.
Fosroc Proofex Engage — Choose the Fosroc option when the project is already standardised on the Proofex tanking and joint system, or where its mechanical cell-mesh bond to concrete is the specified pre-applied membrane.
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Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.