Flat roofs and concrete roof slabs take more punishment in Gauteng than almost anywhere else in South Africa. Summer afternoons push slab surface temperatures well past 60°C, then a Highveld thunderstorm drops the temperature by 20 degrees in minutes. That constant expansion and contraction — thermal movement — opens hairline cracks in screeds, splits old membranes at the joints, and works flashings loose along parapet walls. Add intense UV that embrittles bitumen and acrylic coatings, hail that punctures aged membranes, and ponding water that collects wherever a slab was cast without enough fall, and you have the forces that end the life of nearly every flat roof we inspect.

EcoSeal Roof Waterproofing & Painting Contractors specialises in flat roof waterproofing across Pretoria, Centurion, Midrand and Johannesburg. Where our main waterproofing services page covers everything we seal, this page deals with one thing only: keeping water out of flat roofs and concrete roof slabs — whether that means a new torch-on membrane, a liquid-applied system, renewing an existing torch-on installation, or correcting the slab itself so water finally drains the way it should.

EcoSeal is an approved applicator for SealPro Coatings — a South African waterproofing manufacturer based in Moreleta Park, Pretoria — as well as for Marley Roofing and Mapei. That matters most on a flat roof, because a flat roof gives water time: a pitched roof sheds rain in seconds, but a flat roof holds it against every joint, crack and upstand until it finds a way in. On concrete slabs we install SealPro’s reinforced ArmTec HyperFlex slab system to manufacturer specification — the correct primer, reinforcement and topcoat in the correct sequence, not a single-product patch.

Signs your flat roof needs waterproofing

Flat roof leaks rarely announce themselves directly above the drip. Water travels along the slab, the screed and the ceiling void before it shows, which is why the earliest warning signs are usually on the roof surface itself, not inside the building. Book an inspection if you notice any of the following:

• Ponding water that is still standing on the roof 48 hours after rain — the single biggest accelerator of membrane failure.
• Damp patches, water stains or peeling paint on ceilings and the tops of interior walls, especially after a storm.
• Blistering or bubbling in the existing membrane — trapped moisture vaporising under the waterproofing layer.
• Cracked, lifting or wrinkled torch-on, particularly at laps, corners and where the membrane turns up against parapet walls.
• Exposed or shiny bitumen where the protective mineral chip or silver coating has weathered away, leaving the membrane open to UV attack.
• Hairline cracks in the screed or slab surface that widen and multiply season after season.
• Vegetation, moss or dark algae streaks — a reliable marker of areas that stay wet.
• White powdery deposits (efflorescence) on the underside of the slab or on parapet walls, showing moisture is migrating through the concrete.
• A musty, damp smell in top-floor rooms and stairwells that never quite goes away.

One of these on its own justifies a look. Two or more usually means water is already inside the slab, and repairs get more expensive the longer the moisture is left to spread.

Flat roof waterproofing systems we install

There is no single “best” flat roof waterproofing system — there is a best system for your slab, its condition, its traffic, its drainage and its budget. These are the four pillars of the flat roof work we do every week across Gauteng, built around the SealPro ArmTec range we are approved to install.

Torch-on membrane waterproofing

Torch-on remains the workhorse of concrete roof waterproofing in South Africa. A bitumen membrane, reinforced with polyester and heat-fused to a primed slab, forms a thick, seamless-at-the-laps barrier that handles foot traffic, temperature swings and standing water. We install new torch-on on new and existing concrete roof slabs. Correct installation is everything: primer coverage, full-bond fusion, generous side and end laps, and membrane turned up and dressed properly into parapet chases — the details where cheap installations fail. Where a tired torch-on roof does not need stripping, we overcoat it with SealPro’s liquid ArmTec Renew system, described in full below.

Liquid-applied membrane systems (SealPro ArmTec HyperFlex)

Liquid-applied waterproofing cures into a fully seamless, elastomeric skin over the entire roof. Because there are no sheet laps, liquid systems excel on complex flat roofs: slabs crowded with plant, pipes, aircon mounts and skylights, where sheet membrane around every penetration multiplies the points of failure. They are also the natural choice for maintenance-driven waterproofing, because future recoats go straight over the existing system without stripping.

Our flagship liquid system for concrete is the SealPro ArmTec HyperFlex slab system — a fully reinforced membrane, not a paint-on coating. The whole roof is reinforced, not just the cracks, which is the difference between a coating that survives a season and a membrane that lasts its design life. The full sequence on a clean, dry slab is:

• Clean and prepare. Remove all loose material, dirt, grease and standing water — no SealPro system is applied over a damp or contaminated substrate.
• Prime with Penetrar. SealPro’s deep-penetrating primer for porous cementitious surfaces soaks into the concrete, binds and strengthens the substrate, seals the porosity and locks the membrane down. Applied to the full slab and left to dry fully.
• Detail the cracks and joints with Flex + StretchSeal. Every crack, movement joint and settlement joint is treated first: SealPro Flex is laid as a wet detail coat and StretchSeal reinforcing membrane embedded into it in a three-coat process. StretchSeal is also embedded at every parapet turn-up, outlet and penetration — the exact points where flat roofs actually leak — before the field of the roof, so the reinforcement is continuous.
• HydroSeal HF at outlets. Drainage outlets and penetrations get HydroSeal HF with embedded StretchSeal strips, because outlets sit at the lowest point and see the most water.
• HyperFlex coat 1. SealPro HyperFlex — a high-elongation elastomeric membrane — is applied to the full surface as the wet bed for the reinforcement.
• ArmTec Mesh rolled into the wet coat. ArmTec Mesh is rolled edge to edge across the entire roof into the wet HyperFlex, with a minimum 50mm overlap at every join. Never dry-laid — it is embedded while the HyperFlex is still wet, so it becomes part of the membrane.
• HyperFlex coat 2. A second coat of HyperFlex goes over the mesh, encapsulating it completely so the reinforcement is fully sandwiched inside the membrane.
• Two coats of HydroSeal HF finish. Once the reinforced HyperFlex layer has cured, two coats of HydroSeal HF — SealPro’s high-build elastomeric topcoat — go down as the final white waterproof membrane. Two coats minimum, always, because a single coat leaves pinholes and inconsistent thickness.

Why the mesh matters is the whole point of the system. Concrete slabs move — they expand in the sun, contract in the cold, settle over time and crack at the joints. A coating painted straight onto that slab tears wherever the concrete opens up. ArmTec Mesh embedded across the full surface turns two liquid coats into one continuous reinforced sheet that bridges those cracks and movement joints, so the membrane flexes with the slab instead of splitting over it. That is what makes it a system rather than a coat of paint. See the full specification on our concrete roof slab waterproofing system page, and the wider SealPro range on our systems page.

Screed-to-fall correction

Sometimes the membrane is not the problem — the slab is. A flat roof should never be dead flat: it needs a consistent fall towards its outlets so rainwater drains within hours, not days. Many Gauteng slabs were cast with too little fall, or have settled and cracked so water now collects in hollows in the middle of the roof. Waterproofing over a ponding hollow treats the symptom and leaves the cause. Where the survey shows chronic ponding, we correct the geometry — low spots built up, falls re-established, and outlets or spitters repositioned or added — so the ArmTec HyperFlex system goes down over a slab that finally sheds water. That is the difference between a system that merely survives and one that lasts its full design life.

Parapet and flashing detail work

Ask any honest waterproofer where flat roofs actually leak and the answer is rarely “the middle of the roof.” It is the edges: parapet walls, upstands, box gutters, expansion joints, outlets and flashings. Parapets take weather from both sides, crack along their copings, and wick moisture down into the slab. Membrane that was never chased into the wall, or flashing that has pulled away, gives storm-driven rain a direct path behind the waterproofing. Every flat roof project we do treats the detail work as a first-class part of the job. In the SealPro system that means 45-degree cement corner flashings at parapet junctions, primed and then reinforced with StretchSeal embedded in Flex at every corner, turn-up, joint and outlet — SealPro treats StretchSeal at details as mandatory, never optional, because the detail is where waterproofing succeeds or fails. We also take on detail-only repairs where the field membrane is still sound but the edges have failed. Our work portfolio includes dedicated box gutter and parapet projects for exactly this reason.

Renewing an old torch-on roof — the ArmTec Renew system

The most common question we get on older flat roofs: the torch-on is visibly weathered — does it all have to come off? The honest answer is that stripping is the last resort, not the first quote. In most cases a tired torch-on roof can be renewed in place with the SealPro ArmTec Renew system, which turns the old membrane into the base layer for its own successor and adds a full new reinforced wear layer — at a fraction of the cost, waste and disruption of a full strip-and-replace.

ArmTec Renew follows the same reinforced HyperFlex logic as the slab system, with one non-negotiable extra step at the start. The sequence over sound torch-on is:

• Clean and strip back the failures. Remove all loose, delaminated or bubbled torch-on and clean the surface thoroughly, so the renewal bonds to sound material only.
• UltraBond WP first — mandatory. SealPro UltraBond WP is a bonding primer applied over the entire torch-on surface before anything else. This step is not optional over torch-on or bitumen: it stops the membrane off-gassing under the new coats and prevents the delamination and blistering that ruin a renewal done without it. HydroSeal HF and HyperFlex can never go directly onto bare torch-on — UltraBond WP always comes first.
• Reinforce the joints with Flex + StretchSeal. All torch-on joints, laps, overlaps and cracked areas are reinforced with StretchSeal embedded in Flex, in the same three-coat detail process used on a concrete slab.
• HyperFlex + ArmTec Mesh. HyperFlex coat 1 goes down as the wet bed, ArmTec Mesh is rolled in across the full surface with 50mm overlaps, and HyperFlex coat 2 encapsulates the mesh — the same full-surface reinforcement that bridges the movement an ageing torch-on roof can no longer handle on its own.
• HydroSeal HF finish. Two coats of HydroSeal HF complete the renewal as the final white waterproof membrane.

The result is effectively a brand-new reinforced liquid membrane sitting on the old torch-on, without the cost, mess and downtime of stripping the roof back to the slab.

When renewal is right — and when it is not

Renewal is usually the right call when the existing membrane is still well bonded to the slab, blistering is limited and repairable, laps and turn-ups are largely intact, and moisture testing shows the slab and screed underneath are dry. In that case ArmTec Renew adds a full new reinforced wear layer for far less than a replacement.

Full replacement is the right call when the membrane has debonded across large areas, water is trapped underneath it (widespread blistering, a soft or spongy feel underfoot), the slab or screed beneath is saturated, or so many overlays and patch repairs have built up that the whole system is failing. Waterproofing over trapped moisture is money thrown away — the new layer blisters just like the old one did. In these cases we strip back to the slab, let it dry, repair cracks and spalling, correct falls where needed, and install a fresh ArmTec HyperFlex system on a sound base.

The deciding evidence, not opinion: adhesion checks, moisture assessment of the substrate, and the condition of the details. We put those findings in the quotation so you can see why we recommended renewal or replacement — and we will tell you when a cheaper renewal is genuinely the better decision, because a renewal that should have been a replacement comes back as a callback.

Our process

Every flat roof waterproofing project in Pretoria and the wider Gauteng area follows the same disciplined sequence — because the failures we are called in to fix are almost always process failures on someone else’s job.

1. Inspection. We walk the roof, photograph every defect, map ponding areas, check laps, turn-ups, parapets, outlets and flashings, and inspect ceilings and top-floor walls inside the building for moisture staining. On-site and remote estimates are available, but flat roofs almost always warrant eyes on the slab.

2. Moisture assessment. Before any system is specified, we establish whether moisture is trapped in the screed or slab. Waterproofing over a wet substrate is the most common — and most avoidable — cause of early blistering and failure, and it is a hard SealPro rule that no product goes over a damp surface. The assessment determines whether the roof needs drying time, localised screed removal, or venting details built into the new system.

3. Surface preparation. The unglamorous stage that decides how long the system lasts. High-pressure cleaning, removal of failed or debonded material, crack, spall and joint repair, fall correction where specified, and the correct SealPro primer for the substrate — Penetrar on porous concrete and screed, UltraBond WP over torch-on or sealed surfaces. Parapets and details are prepared to the same standard as the field of the roof.

4. System installation. The specified SealPro system installed in full — Penetrar or UltraBond WP primer, Flex and StretchSeal detailing at every crack, corner, joint and outlet, HyperFlex with fully embedded ArmTec Mesh across the field, and two finishing coats of HydroSeal HF — laid by experienced applicators to the manufacturer’s specification and wet-film thicknesses.

5. Quality control and handover. We check the finished installation detail by detail — mesh encapsulation, coat coverage, terminations, outlet dressings — and confirm drainage performance. You receive the completed work with photographs and our workmanship guarantee: [GUARANTEE — owner to confirm terms], plus a simple maintenance routine so small issues get caught while they are still small.

Recent flat roof projects

Flat roof and concrete slab waterproofing is the core of what we do, and our project record across Gauteng shows it. A few recent examples from our completed work portfolio:

• PRASA train station roof slab waterproofing & rehabilitation, Pretoria — large-scale rehabilitation of a public-infrastructure concrete roof slab, where the waterproofing has to perform under heavy exposure and constant use.
• Roof slab waterproofing upgrade for McDonald’s, Silverlakes — a trading restaurant that could not afford leaks or downtime, waterproofed with minimal disruption to business.
• SEESA Pretoria roof slab waterproofing — commercial office slab waterproofing in Pretoria, protecting occupied workspace below.

From single garden-cottage slabs to shopping centres and multi-storey residential blocks, the systems change but the standard does not. Browse the full work portfolio for more flat roof, slab, box gutter and parapet projects across Pretoria, Centurion, Midrand and Johannesburg.

Flat roof waterproofing across Gauteng

We waterproof flat roofs and concrete slabs across the whole of Gauteng, from our base in Moreleta Park, Pretoria. Centurion is home turf — you can read about our full service on the waterproofing & roof painting Centurion page — and Pretoria East is on our doorstep, covered in detail on our waterproofing & painting Pretoria East page. From there our teams reach Midrand and the northern Johannesburg suburbs comfortably. Wherever the slab is, the SealPro ArmTec system and the standard of workmanship stay the same.

Flat roof waterproofing FAQ

What determines the cost of flat roof waterproofing per square metre?

Five factors drive the rate: the system specified (new torch-on, a reinforced ArmTec HyperFlex liquid system, or an ArmTec Renew overcoat sit at different price points); the condition of the existing roof (a renewal over sound torch-on costs less than stripping a failed build-up); how much preparation the slab needs, including screed-to-fall correction; the amount of detail work at parapets, box gutters, outlets and penetrations; and access, height and roof size. We quote after inspecting, so the price reflects your roof rather than a generic rate. Request a free assessment via our contact page.

How long does flat roof waterproofing last?

It depends on the system, the installation quality and — critically on the Highveld — whether the roof is maintained. A properly installed torch-on or reinforced ArmTec HyperFlex system on a well-drained slab is a long-term solution measured in many years, and the HydroSeal HF topcoat can be renewed at the end of its life without redoing the reinforced membrane underneath. The two things that shorten any system’s life are ponding water and neglected details, which is why we correct falls and treat parapets and flashings as part of the job, not an extra.

Can you waterproof over old torch-on, or does it have to be stripped?

In many cases, yes — over-coating is possible and often the smarter option. If the existing membrane is well bonded and the substrate is dry, we renew it with the SealPro ArmTec Renew system: a mandatory UltraBond WP bonding primer over the torch-on first — which stops off-gassing and delamination — then the reinforced HyperFlex-and-mesh membrane and a HydroSeal HF finish, all without a full strip. If moisture is trapped under the membrane or adhesion has failed, stripping is the only honest recommendation. The inspection and moisture assessment make that call — see our renewal-versus-replacement guidance above.

My flat roof is leaking now — how quickly should it be repaired?

Treat an active flat roof leak as urgent. Unlike a pitched roof, a flat roof holds water against the defect with every storm, so the volume entering the slab grows each time it rains. Moisture trapped in concrete corrodes reinforcing steel, delaminates screeds and damages ceilings and electrical installations, turning a localised repair into a full rehabilitation if it is left through a rainy season. At minimum, have the roof inspected and made watertight before the next run of storms — permanent systems can then be installed once the substrate has dried.

How often should a flat roof be inspected and maintained?

Have a flat roof checked at least once a year — ideally in late winter or early spring, before the Gauteng storm season — and after any severe hail event. Routine maintenance is simple and cheap: clear leaves and debris from outlets and box gutters, check that water is not standing after rain, and look over laps, turn-ups and parapet copings for early movement. An annual inspection catches the small, cheap repair before it becomes a full rehabilitation, and it protects the validity of your workmanship guarantee.

Do you waterproof both residential and commercial flat roofs?

Yes. On the residential side we waterproof concrete roof slabs on homes, garden cottages, garages and townhouse complexes across Pretoria, Centurion, Midrand and Johannesburg. On the commercial side our flat roof work covers offices, restaurants, shopping centres, residential blocks and public infrastructure — the PRASA, McDonald’s and SEESA projects above are all commercial slab installations. The systems are specified to the building’s use, drawing on the same SealPro ArmTec HyperFlex, ArmTec Renew and torch-on range described here and on our main waterproofing services page.

Ready to stop the leak — or prevent the first one? EcoSeal Roof Waterproofing & Painting Contractors inspects flat roofs across Pretoria, Centurion, Midrand and Johannesburg, and every quotation starts with a proper look at the slab, not a guess.