A Reader Asks About Hot Mop For Waterproofing a Deck

DeckExpert.com answers your questions about deck waterproofing methods and materials for only $25.00.

“I am building a new roof deck as part of a full house remodel and I found you when researching my waterproofing options. My builder is suggesting hot mop, but I am not sure it is an appropriate option for a deck. The deck is on the plywood substrate and will not be heavily used (it is primarily there due to city’s set back requirement), but I still want to make sure that it can withstand light use. We are planning to install modular deck tiles on top of the decking surface.” Marat B San Francisco CA

Hello Marat,

Thanks for writing; you’re wise to have done some research and raise doubts about “hot mop” for waterproofing a roof deck.

Today’s modern deck waterproofing systems from our manufacturer’s provide all in one solutions to your waterproofing dilemma. The decking/roofing systems under Division 7 Pedestrian Walking Decks are all tough durable membranes that can be finished to look like wood, tile, stone etc.

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Alternatively, if you want a wood deck on pedestals above a waterproof surface, walking deck systems are still your best choice. The coatings can be installed and then pedestals can be placed on top of the waterproofing and a deck system built on top. With this method you should allow for being able to remove the decking to clean the waterproof surface periodically of debris. Extra slope over the minimum code required 1/4″ per foot may help flush debris off. I would suggest draining off roof edges rather than roof deck drains (ThunderbirdProducts.com) as debris may clog drains at the worst possible time. If you opt for drains, use a minimum of a 3″ drain and 3″ ABS pipe.

If you review our site, you’ll find lots of information and advice that should be useful in your quest. Make sure to read, understand and meet all requirements for a waterproof deck system and always use Best Practices to go over and above code which is just a bare minimum. For instance, use 1 1/8″ plywood over the minimum 5/8″.

Good luck with your project, Bill Leys The Deck Expert

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