How to choose a waterproof roof coating for emergency leaks and long-lasting repairs
A leaking roof or gutter rarely happens at a convenient time. Whether you've discovered water coming through a flat roof during heavy rain or spotted a cracked roof tile that's starting to let moisture in, choosing the right waterproof coating can help stop damage quickly while protecting your home for the future.
The best solution depends on three factors:
- How urgent the repair is
- Whether the surface is wet or dry
- How easy the damaged area is to access
Bostik's WATERSTOP range offers two effective waterproof repair solutions for different repair situations: WATERSTOP Emergency Waterproof Coating and WATERSTOP Repair Spray.
In this article, we'll explain how waterproof roof coatings work, when to use them, and how to select the best solution for both fast repairs and long-lasting protection.
What is a waterproof roof coating?
A waterproof roof coating creates a protective barrier over damaged or vulnerable surfaces, helping prevent water penetration through cracks, joints, seams and small gaps. They come in multiple forms including brushable paint-like formulas as well as convenient, spray solutions. These coatings are commonly used on:
- Flat roofs
- Gutters and downpipes
- Roof tiles
- Flashings
- Exterior wood
- Masonry surfaces
Once applied, they form a watertight layer that helps protect against rain, frost, and general weathering.
Let's look at the two types of waterproof roof coatings available...
When you need an emergency roof leak repair
Sometimes a leak simply can't wait for dry weather. If water is actively entering through a roof or gutter, Bostik WATERSTOP Emergency Waterproof Coating is designed to provide an instant waterproof seal, even when applied to damp surfaces or during rainfall. No primer is required, making it ideal for urgent repairs when time is critical.
WATERSTOP Emergency can be used on many common building materials, including concrete, stone, wood, metal, zinc, clay, tiles, slate, felt, polystyrene and most plastics. This makes it useful for small, time-sensitive repairs where the aim is to create a continuous waterproof layer over the affected area.
The flexible coating cures into a durable membrane that resists cracking, UV exposure, frost, and temperature fluctuations.
Best for:
- Active roof leaks
- Emergency gutter repairs
- Flat roof damage
- Wet-weather repairs
- Cracks and seams requiring immediate waterproofing
When a repair spray is the better choice
Not every waterproofing job is an emergency. For smaller repairs, maintenance work or just working with awkward locations, Bostik WATERSTOP Repair Spray provides a convenient solution, but should only be applied in a dry period.
WATERSTOP Repair Spray is a waterproofer in a handy, aerosol format that allows users to quickly coat difficult-to-reach areas without additional tools. The spray is particularly useful for:
- Cracked roof tiles
- Gutter joints
- Downpipes
- Exterior wood protection
- General outdoor maintenance
It forms a flexible waterproof barrier that helps stop leaks while protecting surfaces from future weather damage. Once cured, the coating remains resistant to heat and frost, helping deliver long-lasting outdoor performance.
Best for:
- Hard-to-reach areas
- Small roof repairs
- Roof tile maintenance
- Preventative waterproofing
- Quick outdoor repair jobs
Choosing the right waterproofer for you
A simple way to choose the best waterproof coating out of the two WATERSTOP options is to consider the conditions of the repair.
Choose WATERSTOP Emergency Waterproof Coating if:
- The leak needs stopping immediately
- The surface is wet
- Rain is falling or expected
- You need a thicker waterproof membrane
- You're repairing flat roofs or gutters
The coating can be applied directly to wet surfaces and is immediately waterproof after application.
Choose WATERSTOP Repair Spray if:
- The area is difficult to access
- The repair is relatively small
- You want a fast, controlled spray application
- You're carrying out maintenance before leaks become serious
The spray requires no primer or specialist equipment and creates a durable waterproof barrier after curing. However, it can only be applied in dry conditions.
Getting a long-lasting repair
Whichever product you choose, preparation remains important. How long a waterproof coating roof repair lasts depends on the surface condition, preparation, coating thickness and exposure to weather.
Before application:
- Remove leaves, moss, and debris.
- Clean away grease, rust and loose material.
- Ensure that standing water has been removed.
- Apply an even, continuous coating across the damaged area.
For larger cracks exceeding 5mm, consider filling the gap first and reinforcing the repair with flexible scrim embedded into the coating.
Applying a complete, uniform membrane is often the difference between a short-term patch and a long-lasting repair.
Important limitations to consider
Waterproof coatings are highly effective for many roofing and gutter repairs, but they are not suitable for every application.
For example, WATERSTOP Emergency Waterproof Coating should not be used on polyethylene, polypropylene, roof lights or glazing, and is not intended for areas subject to regular foot traffic or permanent water immersion.
Similarly, WATERSTOP Repair Spray is designed for exterior use and performs best when protected from rainfall until fully cured.
Understanding these limitations helps ensure the repair performs as intended to give long-lasting, reliable results.
The bottom line
For urgent leaks in wet conditions, Bostik WATERSTOP Emergency Waterproof Coating offers an immediate waterproof solution that can be applied directly to damp surfaces and even in the rain.
For smaller repairs, preventative maintenance and hard-to-reach areas, Bostik WATERSTOP Repair Spray provides a fast, convenient way to create a waterproof protective barrier.
By matching the product to the repair, homeowners can not only stop leaks quickly but also help protect roofs, gutters and exterior surfaces from future weather damage.
