Deck Waterproofing

What is Deck Waterproofing Systems

Deck waterproofing begins with the decking boards. While composite boards typically need no additional sealing or waterproofing, a wood deck will get plenty of benefits from extra protection. The most common deck waterproof solutions include sealers, coatings, and vinyl membranes.

Wood boards must be maintained and sealed properly. Applying a clear sealant will prevent water from entering the porous surfaces of the wood and reduce the risk of rot.

Deck coatings are various versions of a thick substance made from latex, liquid rubber polyurethane, acrylic, enamel, or similar materials and used for resurfacing. They also do a good job of masking cracks and splinters, but some formulas are more difficult to apply than others. 

Waterproof membranes can be constructed with materials resistant to mould, mildew, and UV. They also provide slip resistance. Some types of membranes feature higher upfront cost than sealers, but at the same time don’t require re-application of fresh coats.

Benefits of Deck Waterproofing

Excessive rain, humidity and moisture can seriously damage the deck's surface. Combined with exposure to direct sunlight, it creates unique thermal stress to the material of the deck. Followed by foot traffic, physical tear and wear, debris, green growth and stains, this set of conditions can significantly shorten the lifespan of the deck. The right waterproofing coatings can prevent the issue before it starts. 

Types of Deck Waterproofing Solutions 

Waterproof decks comprise a waterproof membrane installed over a timber substrate and can collect substantial amounts of water that needs to be drained. Deck substrate is support for membrane deck surfaces. The prevalent type of substrate is plywood, provided that complies with the regulations. 

The most common types of waterproof membranes are deck waterproofing sheets. They come in different sizes and thicknesses, manufactured from PVC, synthetic rubber, or modified bitumen. 

Other types are liquid-applied acrylic and polyurethane. A trafficable surface may be permanent or removable. Each type of membrane features specific performance criteria and installation requirements, suitable to particular deck designs.

Things to Consider 

Timber deck joists and plywood substrate moisture content must not exceed the maximum of 20%. Timber joists must feature minimum H1.2 treatment, while plywood requires minimum CCA treatment and minimum 17 mm of thickness. Sheet edges must be supported and laid with staggered joints, with a maximum spacing of 400 mm, and the void may need to be ventilated.

At the edges of a deck, membranes should be correctly turned up behind wall or balustrade claddings, to a minimum of 150 mm or according to the manufacturer’s specification. Over the deck edge, the membrane needs to be turned down a minimum of 70 mm, packed out from the cladding to form a drip edge. All waterproof deck membranes have to be installed by approved specialists.

The size and the slope of the deck determine the deck waterproofing solution—the smaller the area, the lower drainage requirements. Larger decks need higher capacity membranes and greater slope to ensure that water is drained effectively.

The highest point of the deck waterproofing is a threshold with a minimum height of 100 mm, which can be formed by incorporating a demountable raft. A recessed drain can also be used, designed with sufficient capacity, fall, and drainage.

A slope of 1.5° minimum, must face away from the building. Increasing the fall will support better drainage, but it can also make the deck feel steep. 

Care & Maintenance of Waterproof Decks

Every deck needs periodical inspections. Sealers and coatings also require periodic cleaning. Scrubbing the deck with a biodegradable detergent is an acceptable cleaning method that will not impair the waterproofing. Depending on the waterproof membrane quality, pressure washing may or may not be recommended.