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How to Waterproof a Sun Deck or Rooftop Deck

The picture depicts a rooftop outlook over a city. On the deck, there are two areas for seating.

Rooftop decks, whether constructed from wood or masonry, are becoming an increasingly popular architectural trend in urban residential and commercial buildings. 

As cities continue to evolve and space becomes a premium, decks provide valuable outdoor space without sacrificing building footprint. However, the exposure to weather elements makes these types of structures highly susceptible to water damage.

A proper waterproofing regimen is crucial for the longevity of the deck and the overall structure it is built upon. It’s essential to understand the process of waterproofing your rooftop deck and the different materials and techniques available to achieve the best results.

Assessing Your Rooftop Deck

The picture depicts a primarily wooden rooftop overlooking a city.


Before starting a waterproofing project, it’s important to thoroughly inspect your rooftop deck. Look for signs of water damage like discoloration, peeling paint or soft spots on the deck’s surface. Check for cracks or gaps in the sealant around flashing and joints, as they can allow water to enter. If your deck has a slope, ensure that it directs water away from the building and doesn’t create pools.

Dealing with Existing Wood Decking and Pavers

If your rooftop deck features wood decking or masonry pavers, they will need to be removed prior to the waterproofing procedure. This is essential to ensure thorough sealing of the underlying substrate to provide a robust barrier against water ingress and subsequent damage.

Types of Waterproofing Systems

Liquid-Applied Membranes

Liquid-applied membranes are an effective type of waterproofing system that can be used on rooftop decks. They are commonly made up of a primer coat and two top coats that are applied directly onto the surface of the deck. 

Sheet Membranes

Sheet membranes are another effective option for waterproofing rooftop decks. Typically made from rubber, plastic, or bituminous material, sheet membranes are rolled out onto the deck surface and bonded to the substrate using an adhesive. The sheets overlap at the edges to create a continuous watertight barrier. 

Sheet membranes have the advantage of being highly durable and resistant to UV light, making them an excellent choice for sun decks. However, their installation can be more complex compared to liquid-applied systems, especially around corners and details. 

Deck Coatings

Deck coatings are a versatile and economical solution for waterproofing masonry rooftop decks. One such product that is very effective is DRYLOK® Extreme Masonry Waterproofer.

  • Latex-based product with an easy application process, typically requiring two coats applied with a brush, roller, or sprayer

  • A smooth, waterproof finish works well for exterior masonry surfaces, which makes it an ideal choice for rooftop decks

  • Fills hairline cracks and is resistant to 15 pounds of hydrostatic pressure, which is equivalent to a wall of water 33 feet high.

Not only is it tintable, in order to match various color schemes, but DRYLOK Extreme Masonry Waterproofer is also resistant to UV light to help reduce the risk of color fading and damage from the sun.

Preparing the Rooftop for Waterproofing

Cleaning and Removing Debris

Cleaning and removing debris from your rooftop deck is a critical step in the waterproofing process. Start by sweeping the surface thoroughly to remove loose dirt, leaves and other debris. If there is embedded dirt or stains, use a deck brush and a suitable outdoor cleaner. 

Addressing Structural Issues or Damage

Before moving on to the waterproofing step, any structural issues or damages on the rooftop deck must be addressed.

New Rooftop Sun Deck

If you are installing a new rooftop deck, ensure the existing roof structure can handle the extra weight. You may need to have an engineer evaluate the structure and provide documents that show the underlying structure is sufficient for the new project.

Existing Rooftop Sun Deck

Start by inspecting for any signs of structural issues such as loose, warped or rotten deck boards. If you spot any of these signs, these should be replaced immediately. For masonry pavers, keep an eye out for pavers that have become loose or have shifted out of place. After the waterproofing is complete, these corrections should be implemented. Make sure that any cracks or gaps are filled in.

Filling Cracks and Leveling the Surface

Before you start waterproofing, it’s crucial to take care of cracks and level the surface. Cracks and uneven areas can affect the effectiveness and durability of your waterproofing products. For a reliable solution, check out DRYLOK Pourable Masonry Crack Filler.

It is manufactured specifically to fill and seal minor cracks in concrete surfaces like sidewalks, patios and garage floors. DRYLOK Crack Filler provides a smooth finish that can be painted over once it’s dry, and it’s designed to withstand the elements. Remember to clean the crack and remove any loose material before applying for the best results.

Ensuring Proper Drainage

Adequate drainage prevents standing water, which could lead to leaks, premature wear and tear, as well as structural damage. Begin by examining the slope of the deck. Ideally, your deck should slightly tilt towards the drainage point to facilitate the natural flow of water. 

If your deck is level or has low spots, consider consulting a professional to adjust the slope. Regularly inspect and clean your deck’s drainage system, including gutters and downspouts, to prevent blockages. 

Removing Existing Coatings or Finishes

Before applying new waterproofing, it’s necessary to remove any existing coatings or finishes from the deck surface. These could potentially interfere with the adhesion and effectiveness of the new waterproofing products. Begin by using a paint scraper or a pressure washer to remove loose or flaking paint.

To strip stubborn coatings, consider using a chemical paint stripper specifically designed for deck surfaces. Once the old coating is fully removed, sand the surface to create a smooth, clean substrate for the waterproofing product. Rinse the deck thoroughly to remove any lingering dust or debris, and then allow the surface to dry completely.

The picture depicts a gray rooftop with a fireplace, seating areas and small tables.

The following are general guidelines for applying waterproofing products:

  1. For the best results, it’s recommended to schedule your project when the air and surface temperatures are 50°F or higher to help ensure the optimal outcome and desired quality.

  2. Choose a rain-free period for application.

  3. Before and during the application of DRYLOK Extreme Masonry Waterproofer, make sure to thoroughly stir the product without thinning it.

  4. Use a three-quarter-inch nap roller, a DRYLOK Brush or a quality nylon bristle brush for the first coat on bare masonry. If using a brush, work the waterproofer into the masonry’s pores and make sure to fill all pores and pinholes. If using a roller, back brush the first coat for the same result.

  5. Allow the first coat to dry for 2 to 3 hours before applying a second coat.

  6. The second coat can be applied using a roller, brush or sprayer. Note that a minimum of two coats is required for warranty waterproofing. After the second coat, carefully inspect the entire surface for pinholes and apply an additional coat if needed.

If leaking persists after two coats, it indicates that pores or pinholes are still open, and these areas should be painted again.

Post-Installation Considerations

Regular Inspections and Maintenance

The cornerstone of a healthy rooftop deck is regular inspections and proactive maintenance. Inspecting your deck for signs of wear or damage, such as cracking, peeling, or discoloration, should be done at least twice a year, ideally in spring and fall. During the inspection, check for loose railings, protruding nails, or rot and take prompt action to resolve any issues found.

Cleaning Schedule and Products

A clean deck not only looks good but also lasts longer. Plan to clean your deck thoroughly at least once a year. A mild, non-abrasive deck cleaner, suitable for the deck material, is ideal for lifting dirt and mildew without damaging the surface. Make sure to rinse the deck thoroughly after cleaning to avoid any residue build-up which can lead to staining.

Handling Minor Repairs

Address minor repairs as soon as they arise to prevent further damage. This can include filling small cracks with a suitable filler, replacing loose nails with deck screws or sanding rough areas. Always follow the manufacturer’s instructions when using repair products.

Reapplying Waterproofing

Depending on the weather exposure and deck usage, you may need to reapply a waterproofing treatment every 2 to 3 years. Ensure that the deck surface is clean and dry before reapplication. Follow the manufacturer’s instructions for the best results.

Protecting Rooftop Furniture and Features

Furniture and other features on your rooftop deck are exposed to weather and need protection as well. Consider using covers for furniture when not in use and apply suitable protective treatments to other features as necessary.

Trust in DRYLOK for the Best in Waterproofing for Your Rooftop Deck

When it comes to safeguarding your rooftop deck from the elements, DRYLOK is a reliable and long-lasting solution. Our waterproofing products are designed with durability and ease of use in mind to help ensure that your deck remains dry, safe, and in excellent condition, regardless of the weather.

Contact us today to locate a retail supplier near you!