How do you waterproof a leaking roof?
Short answer: clean and prime the surface, seal the cracks and joints, then apply a flexible waterproofing system — most commonly a liquid rubber coating, a reinforced membrane, or a bitumen sealer. The right choice depends on your roof type, the size of the problem, and your budget. This guide explains each option, how they compare, how much product you’ll need, and how to apply a liquid-rubber system yourself.
A roof leak almost always starts at a weak point — a hairline crack in the screed, a lifted seam, a perished old membrane, a gap around a pipe or parapet, or a rusted screw hole on a steel roof. Water finds that gap, sits, and works its way in. Waterproofing fixes the problem by laying a continuous, flexible, UV-stable skin over the whole surface so there are no gaps left for water to exploit. Do it properly once and a flat or low-pitch roof can stay watertight for years.
Why roofs leak in South Africa
- Thermal movement — our big day-to-night temperature swings make roofs expand and contract, cracking rigid screeds and old brittle coatings.
- UV breakdown — harsh sun perishes old torch-on and acrylic membranes until they craze and lift.
- Ponding water — flat roofs that don’t drain fully leave standing water that eventually finds any weak spot.
- Failed detailing — the joints, parapets, pipe penetrations and flashings are where most leaks actually start, not the open field of the roof.
Your waterproofing options compared
There are four main approaches for homes and light commercial roofs in South Africa:
| System | How it works | Best for |
|---|---|---|
| Liquid rubber coating | A flexible rubberised coating rolled or brushed on, often with a reinforcing membrane embedded between coats. Forms one seamless skin. | Flat & low-pitch concrete roofs, parapets, box gutters, DIY repairs — the most versatile all-rounder. |
| Reinforced membrane system | A bonded-polyester or fibre membrane laid into a waterproofing coating to add strength and bridge cracks and joints. | Roofs with movement, cracks or busy detailing that need extra reinforcement. |
| Bitumen / flashing sealer | Bitumen mastic and aluminium/bitumen flashing tape seal joints, flashings, gutters and penetrations. | Spot repairs, metal roof seams, flashings, gutters and around pipes & chimneys. |
| Reflective / roof paint | A waterproofing and heat-reflective topcoat that protects the system below and cuts heat gain. | Finishing and protecting a waterproofed roof, and reflecting heat off IBR & concrete. |
Liquid rubber vs torch-on vs membrane: which should you choose?
For most home and small-commercial jobs, a liquid rubber coating is the easiest and most forgiving choice. It’s applied cold with a brush, roller or squeegee — no open flame — so it’s safe to DIY, it gets into every awkward corner, and it forms one seamless membrane with no seams to lift.
Torch-on (heat-applied bitumen sheeting) is tough and well proven, but it needs a gas torch and real skill to lap the sheets correctly, and the laps are exactly where failures start — it’s best left to experienced contractors.
Reinforced membrane systems sit in between: you still apply a liquid coating, but you embed a bonded-polyester membrane into it over cracks, joints and the whole field for extra strength. This is the go-to when a roof moves or has a lot of detailing. For the actual leak points — seams, flashings and pipe penetrations — bitumen mastic and flashing tape seal them before you coat.
How much waterproofing do I need?
Coverage depends on the product and how porous your surface is, so always check the tin, but as a rule of thumb for a liquid rubber system:
- Measure your roof area in square metres (length × width), and add about 10% for waste, laps and detailing.
- Allow for multiple coats. A proper system is usually a primer/first coat, a reinforcing membrane layer, then one or two topcoats — so you’ll use noticeably more than a single-coat estimate suggests.
- Typical total usage for a rubberised coating lands around 1.5–2 litres (or kg) per m² across all coats on a sound surface; rough or porous surfaces drink more.
- Don’t under-buy the membrane. If you’re reinforcing, match the membrane roll area to your roof area plus overlaps.
When in doubt, round up — a thin, under-applied coat is the single most common reason a DIY waterproofing job fails early.
How to apply a liquid rubber waterproofing system (step by step)
- Clean the surface. Sweep, then wash off all dirt, moss, chalking and loose old coating. The surface must be sound, dry and dust-free — adhesion is everything.
- Repair and prime. Rake out and fill cracks, and seal joints, flashings and penetrations with bitumen mastic or flashing tape. Prime porous surfaces so the coating bonds instead of soaking in.
- First coat. Brush or roll on an even base coat, working it well into the surface and all the detailing.
- Embed the membrane. While the first coat is still wet, lay your reinforcing membrane into it over cracks, joints and the full field, overlapping the edges, and coat straight over the top so it’s fully saturated with no dry patches or air bubbles.
- Topcoats. Once touch-dry, apply one or two more coats, ideally cross-wise to the previous coat, to build a thick, continuous film.
- Finish & reflect. For flat concrete and IBR, finish with a reflective roof coating to protect the system from UV and cut heat gain.
Work in dry weather with no rain forecast for the curing window, and don’t coat in the heat of the day on a scorching surface.
Different roofs, different approaches
- Flat & low-pitch concrete — the classic liquid-rubber-plus-membrane job; finish with a reflective coat against ponding and UV.
- IBR & corrugated steel — seal the screw holes, overlaps and ridge first, then coat; a reflective topcoat makes a big difference to interior heat.
- Parapets, box gutters & flashings — reinforce every internal and external corner with membrane; these are the highest-risk leak points.
- Asbestos sheeting — don’t disturb or grind it; encapsulate and protect it with a dedicated coating such as RCM Asbestos FibreLock.
The benefits of a liquid rubber system
- Seamless & flexible — one continuous skin with no laps to lift, and it stretches with the roof instead of cracking.
- Cold-applied & DIY-friendly — no open flame, just a brush, roller or squeegee.
- Gets everywhere — coats around pipes, parapets and awkward detailing that sheet systems struggle with.
- Re-coatable — when it eventually weathers, you simply clean and re-coat rather than stripping and starting over.
Things to consider before you start
- Surface prep makes or breaks it. Most failures are adhesion failures — time spent cleaning and priming is never wasted.
- Weather window. You need dry conditions through application and curing; check the forecast before you open a tin.
- Don’t skimp on coats or membrane. Build the specified film thickness; thin is the enemy of waterproof.
- Match the product to the surface. Concrete, metal, asbestos and bitumen each have a best-fit coating — ask us if you’re unsure.
How to choose: products for the job
Match the product to your roof and the scale of the job:
- All-round flat-roof waterproofing — a rubberised sealer kit like the Eco Rubber Rubberized Waterproof Sealer DIY Kit (coating plus membrane in one), with a contractors pack for bigger areas.
- Heavy-duty & reflective coatings — the RCM range, including RCM ImvulaPro Waterproof Coating and the heat-reflective RCM Reflective Barrier Coating.
- Reinforcing membrane — RCM bonded-polyester membranes in various widths and lengths.
- Rubber-seal roof kits — the POWR Rubber Seal waterproofing kits in a range of colours.
- Joints, flashings & gutters — Flash Harry bitumen mastic and aluminium flashing tape.
See the full Waterproofing & Coatings range and waterproofing paints for everything in one place.
Frequently asked questions
What is the best way to waterproof a flat roof?
For most homes, a cold-applied liquid rubber coating reinforced with a bonded-polyester membrane is the best all-round method. It forms one seamless, flexible skin with no seams to lift, is safe to apply yourself with a brush or roller, and can be re-coated when it eventually weathers.
Liquid rubber vs torch-on membrane — which is better?
Liquid rubber is easier and safer for DIY and small jobs because it’s applied cold and seamless, with no laps to fail. Torch-on bitumen sheeting is durable but needs a gas torch and skilled lapping, so it’s better suited to experienced contractors on larger roofs.
How much waterproofing do I need per square metre?
As a rule of thumb, a rubberised liquid system uses roughly 1.5–2 litres or kg per m² in total across all coats on a sound surface, with rough or porous surfaces using more. Measure your roof area, add about 10% for waste, and always check the specific product’s coverage on the label.
Can I waterproof a roof myself?
Yes. A liquid rubber system is designed for DIY: clean and prime the surface, seal the cracks and joints, apply a base coat, embed a reinforcing membrane, then add topcoats. The keys are thorough surface prep, dry weather, and building up the full specified thickness.
How long does roof waterproofing last?
A correctly applied liquid rubber system on well-prepared, sound surfaces typically lasts several years, and because it’s re-coatable you simply clean and refresh it rather than stripping it off. Lifespan depends heavily on surface prep, film thickness and UV exposure — a reflective topcoat helps it last longer.
What is the best waterproofing paint for a roof in South Africa?
For heat and UV, a reflective barrier coating over your waterproofing performs well on flat concrete and IBR. For the waterproofing layer itself, a rubberised membrane coating (such as Eco Rubber or the RCM range) gives the flexibility South African roofs need to handle big temperature swings.
Need help choosing the right system?
Browse the full Waterproofing & Coatings range — liquid rubber, membranes, reflective coatings and flashing — or tell us your roof type and size and we’ll spec the right products and quantities. Contact the Securadeal team and we’ll help you get it watertight the first time.
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