Leaks, cracks or puddles on your flat roof? Sounds like it needs waterproofing! What can you buy to do the job properly? There are plenty of products out there, so let’s help you get what you need to successfully complete your project.

Flat roof technology has come a long way since the 60s and 70s. Thanks to modern materials and stylish glazing, today’s flat roofs are the epitome of architectural style. Some are even being used in new and unusual ways, from sun terraces and balconies to green roofs for budding urban gardeners.

But apart from their stylish design features, the other thing that’s moved on considerably is the technology used to keep them weather-proof. Once flat roofs were notoriously prone to leaking and the problem could only be solved with a boiling cauldron of tar. These days there are patch repair kits, liquid rubber membranes and even quick, efficient waterproofing paint such as paint-on acrylics that last for ages – and can even be applied in damp weather.

From short-term fixes to 15-year solutions, Roofing Superstore has the answer to all of your flat roof waterproofing dilemmas. Armed with our products and accessories you can be sure your flat roof will keep your home dry for years to come. All you need is a bit of DIY knowledge, a good head for heights and this handy buyer’s guide.

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Can I repair it or do I need a whole new roof?

That really depends on exactly what’s wrong with it and the age and history of the roof. If you only have a small leak or damaged patch, a complete re-roofing may not be necessary – and with today’s modern products, such minor repairs are well within the reach of most homeowners. These days, even patch repairs are tough and durable and, at the very least, will buy you some time while you think about what to do.

Patch repairs being applied to a roof

Even if it’s the whole surface that needs waterproofing, some of Roofing Superstore’s more extensive products are easy to apply and are designed to be a long-term solution. For example, the Acrypol range can be painted onto virtually any flat roof surface and its Acrypol 15 system is so durable that it’s guaranteed for 15 years.

A 3D render of flat roof insulation in a flat roof

So when will you require a new roof? Well, you might want to consider re-roofing should you wish to improve your flat roof’s insulating properties. Adding more insulation will protect the room below from condensation and may lower your heating bills, paying for itself in the long run. If you wish to change the use of your flat roof, perhaps by transforming it into a balcony or roof garden, a new roof could make the existing structure strong enough to hold the weight of your guests at your next rooftop barbecue.

How to find a leak in a flat roof

If you have to put a bucket in exactly the same spot each time it rains, you’ll want to find out exactly where your leak is coming from. The source of flat roof leaks can be hard to locate when you’re actually up there, so a good tip is to do your detective work inside the house. With a tape measure, measure the distance from the drip in the ceiling to the nearest wall. Then, when you’re on the roof, measure the same distance. That should lead you straight to the root of the problem.

How to inspect your flat roof

If you suspect your flat roof has a waterproofing issue, you’ll need to head up to the roof itself. But what should you be looking out for? Follow these tips for a successful flat roof inspection…

1. Be safe

Before attempting any inspection of your flat roof, make sure that it’s completely safe to do so and, if you’re at all unsure, call out a professional. If you need to use a ladder, make sure it’s well-secured and don’t step onto the roof itself if you have any doubts about its condition. If your flat roof doesn’t currently have an anti-skid coating, remember that it could also be very slippery and you may have to use temporary boards.

2. Time it right

Try to do your flat roof inspection after a period of rain. This will help you spot any areas of ponding (big puddles) and highlight any drainage issues.

3. Check the guttering

Sometimes what appears to be a leak in a flat roof actually turns out to be problems related to the guttering. That’s why you should check your gutters and drains are free from dirt and debris while you’re up there.

4. Know what issues to look out for

Once you’ve checked the gutters, it’s time to look at the flat roof surface itself. Things to look out for include blisters (bubbles in the membrane), ponding, cracks or splits. You may find that the coating has cracked and formed a pattern that looks like the skin of an alligator. Called ‘alligatoring’ this is a common condition caused by sun exposure and excess moisture. Left untreated it could lead to splits over time.

How do you know what’s causing the problem?

Spotted something on your flat roof and don’t know what it is? We can help you identify some common trouble spots, and give you tips on what to do.


Have you noticed any air bubbles on your flat roof? This is referred to as blistering, and it happens when small pockets of air or moisture get trapped beneath the membrane. Blisters can expand in the sun as the warmth heats the air inside, which stretches the membrane further. But despite their appearance, it’s actually best to leave blisters alone if they’re still intact. If they do happen to pop, cut away the broken material then apply a patch repair such as Acrypol Plus or an adhesive patch kit such as Karnak Patch N Go, making sure the damaged area is well covered.

Blistering on roofing membrane


If a puddle stands on a flat roof for 48 hours or more it’s known as ponding. It’s a common problem in flat roofs. This may not be a problem, but over time it could cause stress on the membrane and lead it to fail, letting in the dreaded moisture. To avoid this, keep gutters clear so that water can quickly drain away.


If your flat roof is starting to look like the hide of an alligator, water, debris or sun damage has cracked the bitumen coating. This is what causes the alligatoring roof effect. Eventually, this will split and let moisture in. For this, you need a new roof waterproofing solution, such as liquid rubber or Acrypol.

Alligatoring on a flat roof

For more information on blistering, ponding and alligatoring, read our guide to common flat roofing problems.

The problem and the solution

Not sure which one of Roofing Superstore’s flat roof waterproofing solutions is best for you? We’ve made a list of common issues and matched them with the product that can help.

The problem: You need to fix a roof leak quickly but it’s wet outside

The solution: Acrypol Plus

For this kind of emergency, you need a quick, easy-to-apply waterproofing solution you can even use in wet conditions. Step forward Acrypol Plus. Whereas many waterproofing solutions need the flat roof to be totally dry to be effective, Acrypol Plus can even be used in damp weather and can fix cracks of up to 10mm wide. Although the product is available in larger amounts (such as 5kg or even 20kg cans) you won’t need nearly as much for just a small flat roof leak repair. That’s why we’d recommend Acrypol Plus in the smaller 2.5kg can. Even better, it comes in a medium grey shade. This is specifically designed so that the colour will blend in seamlessly with your existing roof.

A tin of Acrypol + roof coating with a before & after example in the background

How does Acrypol Plus work?

Acrypol Plus is an acrylic resin that’s dispersed in a solvent so it looks like a semi-liquid paste. When dry it turns into a tough elastic overlay that stops any moisture from moving through it. Its chemical structure is designed so that even trapped moisture can evaporate safely away, so you’ll avoid any blistering. This particular product also has added fibres that interlace together, helping it to fill and bridge gaps, while still remaining flexible.

Acrypol Plus is suitable for:

Acrypol Plus can be applied onto almost any kind of flat roof surface from asphalt and bitumen to felt. It’s a handy product to have around the house as you can also use it to fix gutters, metals, concrete and masonry.

How to apply Acrypol Plus:

First, remove all loose dirt, moss and standing water from the area of your roof that needs to be treated. Apply the product with a brush or roller. While still damp, work it into the surface to remove excess moisture, then brush it out fully. For a more detailed Acrypol application guide, take a look at the Acrypol application guide on the product page.

The problem: You want to turn your flat roof into a terrace so you need non-slip flooring

The solution: Acrypol Quartzdeck

Before turning your flat roof into a sun deck, remember that it may not have been designed to bear the weight of lots of people. Seek specialist advice first as you may need to reinforce the existing structure. Assuming you’ve got the go-ahead, Acrypol Quartzdek is a great addition to your grand design. In a choice of beautiful colours, not only does it make an attractive floor covering for your new balcony, but it’s designed to be anti-slip, and it can waterproof your flat roof, all at the same time.

A before & after of Acrypol Quartzdeck on a roof

How does Acrypol Quartzdek work?

A waterproofing and anti-slip solution in one, Acrypol Quartzdek contains real quartz granules that you sprinkle over a tough waterproof coating, all sealed and bonded together with a final layer of resin.

Acrypol Quartzdek is suitable for:

You can use Acrypol Quartzdek anywhere that needs an anti-slip covering such as balconies, walkways, exterior stairs, risers and roof gardens. It’s suitable for use on practically any flat roof covering.

How to apply Acrypol Quartzdek:

First, choose the colour of your granules. There’s an attractive silver mixed with light grey and black or a striking red mixed with light grey and black. Then on a clean, dry flat roof surface, apply the Quartzdek Primer over the entire area. Let it dry for one to two hours, then apply the Quartzdek Resin in strips half a metre wide. Sprinkle the quartz granules into the wet coating. Allow to dry overnight, then apply a final coat of Quartzdek Resin over the top. This also needs to dry overnight, but the next day your new flat roof terrace will be ready for you to enjoy.

The problem: You need to waterproof a complicated flat roof that has lots of details and abutments

The solution: Liquid rubber

Flowing and flexible, liquid rubber membranes are the painless way to completely waterproof a flat roof that has lots of complex features. Totally eco-friendly and with a long life expectancy, Roofing Superstore has plenty of options to choose from when it comes to rubber for roofs. There’s an all-purpose brush-on Cromar whose RubberCoat is designed for hand application, making it perfect for DIY-ers. Or go for top-of-the-range EcoProof which is well-known for its exceptional adhesion properties, meaning it will fully bond to whatever roof covering you already have. Finally, there are Soudal products that are great for emergency rubber repairs.

A flat roof coated with liquid rubber

How does liquid rubber work?

Far more flexible than traditional bitumen, when the liquid rubber is applied it cures to form an elastic coating that’s able to stretch and return to its original shape without cracking or splitting. It’s almost like getting a whole new roof but at a fraction of the cost. In fact, it’s estimated that liquid roofing is 70% less expensive than a brand-new roof.

Liquid rubber is suitable for:

Liquid rubber can be used over any flat roof covering, even concrete, cement and asphalt.

How to apply liquid rubber:

To achieve a perfect finish, adding some liquid rubber optional extras before you start can help make your waterproofing even more durable. First, use some liquid rubber mastic adhesive to fill small gaps, then apply liquid rubber tape to cover joints, large gaps, pipework and vents. Using a flood coat can help the liquid rubber stick to trickier surfaces such as built-up felt, fibre cement sheets and semi-porous surfaces such as masonry. Then apply your liquid rubber membrane in thin layers, allowing each to fully dry and cure. Finally, add some kind of liquid rubber trim angled so that it deflects rainwater away from the roof.

The problem: You have a wide crack in your roof

The solution: Acrypol Plus and Acrypol Scrim

Acrypol Plus can be used by itself to fix cracks up to 10mm wide. But if your crack is wider than this, you need the help of Acrypol’s flexible mesh – otherwise known as scrim. This reinforcement mesh can be incorporated into just one application of Acrypol Plus to bridge over major splits and cracks in roofs and gutters.

Acrypol scrim being applied to corrugated roofing with a paint brush

How do Acrypol Plus and Acrypol Scrim work?

If you’re filling in a large crack in a flat roof, you need a type of mesh that has added flexibility. That’s because you still want the flat roof substrate to be able to move in any direction, without breaking its watertight barrier. Acrypol Scrim allows you to do just that because it increases both the tensile strength and the mechanical resistance of the waterproof coating.

Acrypol Plus and Acrypol Scrim are suitable for:

The Acrypol Plus and Acrypol Scrim solutions can be used on most types of flat roofs from felt and asphalt to asbestos and metal. For single-ply and fibreglass roofs, you’ll need to do a compatibility test first.

How to apply Acrypol Plus and Acrypol Scrim:

Acrypol flexible reinforcement mesh is easy to work with as the product can just be cut with scissors. First, remove any dirt, then apply one coat of Acrypol Plus to the problem area making sure you go at least 20cm beyond the crack in every direction. Embed a small piece of Acrypol Scrim into the Acrypol Plus with a brush to make it flat, then apply another coat of Acrypol Plus over the top. Acrypol Plus comes in grey, black and white so you can get the finish that matches your existing roof coverings.

The problem: Your flat roof is too slippery and dangerous to walk on

The solution: DeckProof Anti-Skid & Waterproofing Kits

If your flat roof is so slippery that your window cleaner is refusing to clean your bathroom windows, you need to apply some kind of anti-slip surface. For this, you have two options. You can just apply DeckProof Anti Slip Liquid Roof Membrane over the top of your existing membrane (although this does not have any additional waterproofing properties) or buy one of the Deckproof Rapid Curing Anti-Skid Roof Waterproofing Kits which ensure your roof is both waterproofed and anti-skid.

DeckProof Anti Slip Liquid Roof Membrane on a flat roof

How do anti-skid kits work?

Anti-Skid kits have everything you need for a fully bonded, seamless anti-skid flat roof. Just apply two coats and your roof will be anti-slip and ready to walk on. The kits come with detailing primer and joint tape. For a total solution with both anti-skid and waterproofing properties, anti-skid kits with waterproofing come in black or grey options and also contain detailing primer and the anti-skid coating, but also have a waterproof coating too.

Anti-skid kits are suitable for:

You can apply both products to asphalt, masonry, felt and plastics.

How to apply anti-skid kits:

They’re easily applied in two coats. Each coat takes just 20 minutes to cure and they provide an attractive surface once they’re finished.

The problem: You need to repair a small patch of damage and have no DIY skills

The solution: Flat roof repair kits

If you’re not particularly handy, you’ll need something really easy to use. Luckily,  Roofing Superstore has not one but two products available. First, there are Patch-N-Go repair kits from market leader Karnak. These are very effective and don’t require any DIY knowledge whatsoever.

Tekcryl paint-on waterproofing solution being applied to a flat roof with a paint brush

How do flat roof repair kits work?

The easiest flat roof repair that money can buy, the stick-on patches work very much like plaster – you just peel away the backing and apply the patch to the damaged area of your roof.

Flat roof repair kits are suitable for:

There are two different stick-on patches available, one for EPDM and rubber roofs, and one for felt.

How to apply flat roof repair kits:

Make sure the surface is clean and dry, and that you’ve removed any oil and grease. If using the patches, take them out of the pack and peel off the film backing. Then press down onto the roof, applying extra pressure with a roller to help it stick. If using acrylic paint, just brush it on. It dries in two to three hours but will be waterproof immediately.

The problem: You need a long-term, affordable waterproofing solution

The solution: Acrypol System 10

If your flat roof has so many cracks and blisters it’s starting to resemble the surface of the moon, you need a whole roof solution, and one of the most durable on the market is Acrypol System 10. With a 10-year life expectancy, it can be installed even when it’s damp and doesn’t involve you making any structural changes to your roof, making it great value for money.

A before & after image of Acrypol system 10 on a flat roof

How does Acrypol System 10 work?

System 10 uses a tough, acrylic resin that stops water from penetrating but allows any moisture to escape at the same time. With both undercoats and topcoats available in UV-protecting solar white or minimalist grey, you apply the system in seven simple steps. Fast and easy, it gives a totally seamless finish even around problem areas prone to leaking such as upstands or vents.

Acrypol System 10 is suitable for:

You can use System 10 on practically any existing roof membrane.

How to apply Acrypol System 10:

Use a stiff brush to remove all dirt and debris, then pressure wash the whole area. Apply Acrypol Sealer, then use a silicone filler on any splits. Apply the Acrypol System 10 undercoat and while wet, use the Acrypol flexible mesh scrim and smooth flat. Finally, apply the System 10 topcoat in your chosen colour with a paintbrush.

The problem: You need a long-term waterproofing solution for a commercial property

The solution: Acrypol System 15

If you’re a business owner and need a large-scale solution for your industrial property, Acrypol 15 is perfect for the job. Like Acrypol System 10, it’s fast and easy to install, but it also comes with added features that make it even more long-lasting.

A before & after image of Acrypol system 15 on a flat roof at Salford Royal University Teaching Hospital

How does Acrypol System 15 work?

Acrypol System 15 has a tough acrylic resin at its heart, but as part of its 15-year long-lasting solution, it also comes with the Acrypol Bedding Coat into which you incorporate the rot-proof reinforcing mesh scrim, which makes it even more flexible and durable.

Acrypol System 15 is suitable for:

As you can use System 15 on practically any existing roof membrane, it means you won’t have to replace any roof structures. That’s perfect for commercial properties as it means the business can carry on as usual.

How to apply Acrypol System 15:

First, apply Acrypol Sealer, then use the Acrypol Bedding Coat into which you incorporate the Acrypol flexible mesh scrim. Then apply the Binding Coat, before finishing off with the System 15 Finishing Coat.

Check out our wide range of flat roof waterproofing products for more information about our latest waterproofing solutions here.

Tips for preventing flat roof leaks

Prevention is always better than cure when it comes to flat roofs. So deal with little problems before they turn into big expensive ones.

  • Try to inspect your flat roof twice a year. March and November are good months to do it, both before and after winter
  • Limit access to your roof unless it’s been designed to take regular footfall. If you need to walk on it, use temporary boards
  • Record the size and position of any blisters or puddles to know if any of these problems are getting worse
  • Check details such as upstands, flashings, joints and edge trims and make sure the roof isn’t sagging at the joists
  • And finally, keep your roof clean. Any build-up of moss or algae can contribute to trapped moisture that can lead to damage to the waterproof membrane

Buy with confidence from Roofing Superstore. For advice and help using waterproofing materials on flat roofs, contact our customer service team on 01752 692 760 or use the live chat. 

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