How to seal a flat roof: The definitive guide

Discovering the early signs of a leaking flat roof can be stressful but fear not – we’re here to guide you through the ultimate method to waterproof and seal it. Below, we’ll walk you through the signs of a leaky flat roof and provide a step-by-step process for sealing it effectively and keeping water at bay.

From obstructed gutters to the impacts of severe weather conditions, below are key indicators that your roof needs some TLC.

Ponding water

You’ll usually spot this roughly 48 hours after rainfall on the roofs surface – and the longer it’s there, the higher the risk of water leaking through.

Blocked gutters

Often caused by a build-up of dirt, debris and green growth, obstructed gutters can result in water overflow and roof damage.

Dirt, debris and green growth

Ponding, dirt, debris and green growth on the surface of your flat roof for a long period of time can have a detrimental effect on your flat roof, again causing water damage.

Seams and overlaps of roofing material

Common area leaks often originate from the seams or overlaps of the roofing material, which should be checked on once or twice a year.

Dark brown patches

These are indicative that there is damp developing from your damaged flat roof. This could be a big or small repair, so the sooner it’s seen to, the better.

If you’ve spotted any of the above issues with your roof, give the tips below a go. But remember, if you’re ever unsure, you can call a professional for help and advice.

What you’ll need:

• Ladder
• Hard bristle broom
• Paint scraper
• Soft bristle broom
• Safety glasses
• Safety gloves

Step 1: Start Cleaning

Using a ladder, climb safely onto your roof – be mindful and make sure the roof can hold your weight. Once you’re up there, start cleaning! Clear away any loose dirt or debris using a hard bristle broom, as well as any stagnant water – although you can apply some roof coatings onto a wet surface, we advise you apply the roof coating onto a dry roof.

If you come across any stubborn dirt, moss, or green growth, we recommend you use a paint scraper, it can be more effective than just using a hard bristle broom.

Step 2: Roll Out the Mesh Scrim

Firstly, you will need enough mesh scrim to cover the entire flat roof. Starting in a corner, roll out the mesh scrim parallel to the roofs edge. Once you’re at the opposing edge, cut it slightly shorter than the roofs edge.

In the following steps we’ll be splitting the how-to process into sections. Section 1 consists of your starting point, usually a corner attached to the house, to the centre of the flat roof. Section 2 is from the centre of the flat roof to the roofs edge.

Steps 3-6: Part 1 of the Application

3. Roll up the mesh scrim from the corner to the centre, exposing the roof surface.

4. Apply an even coat of roof coating with a soft bristle broom.

5. Unroll the mesh scrim onto the wet coating.

6. Apply a second coat, covering the mesh scrim completely.

Steps 7-11: Part 2 of the Application

7. Repeat the process on the other half of the mesh scrim, ensuring the roof is dry.

8. Apply the roof coating onto the newly exposed roof.

9. Unroll the mesh scrim onto the wet coating.

10. Cover the mesh scrim with a second coat until invisible.

11. Repeat the process, overlaying the next strip of mesh scrim parallel to the freshly laid one.

Step 12: Wait to dry

Allow the roof coating to dry completely, which may take up to 24 hours.

Step 13: Optional second coat

You may find you have pinholes in your mesh scrim, which means it was not completely covered by the application. Therefore, a second coat is recommended after waiting for it to dry. Start in the corner and work your way back – make sure you don’t trap yourself!

Investing time in this thorough process ensures long-lasting protection and a roof that will last, leaving you to admire a leak-free flat roof and enjoy years of worry-free maintenance. Check out our full range of roofing repair products, here: Roof repair products