What Deck Flashing Is For (Hint, It Ain’t for Waterproofing)

Here at DeckExpert.com, I often hear someone say “the flashing leaked and the deck failed”. I always ask, how did the flashing leak? In my opinion, if the deck waterproofing system is installed in such a manner that the entire piece of flashing, the horizontal piece nailed to the deck and the vertical leg that goes up the wall is completely embedded in waterproofing, the flashing basically cannot leak. Drip edges covering the building materials below won’t leak unless the coating has lost it’s bond with the metal. I often find that happens when gutters are nailed through the drop of the drip flashing and the metal is deflected.

The misnomer in my opinion in the industry is to think of flashing as “waterproofing”. It is not primarily waterproofing. What the flashing is for is to provide a termination point for the deck waterproofing system to end to. Metal flashing is simply what we use to do that.

Now let me clear, the flashing’s still must be integrated properly into/with contiguous weather resistant barriers that are being installed by other trades-where building paper comes down and over the flashing for the deck. Sequencing is essential when it comes to installing weather barriers and typically the low slope roof and deck areas are weathered in first.

Edge/drip flashings still must be installed in a manner that they are placed over building materials below them so water runs over, away and off.

Flashing materials are commonly galvanized/bonderized metals, copper and stainless steel. When using any of these, proper preparation of the metal is essential prior to terminating the coating to it. Bright shiny galvanized I don’t recommend at all as it’s very difficult to clean and prep properly in the field for our work’s requirements. I recommend “bonderized” metal flashing instead. It’s basically clean so it usually just needs to be wiped down with a damp rag to remove dust and contaminants.  Copper and stainless steel both require being sanded heavily to “etch” the metal. I use a 4″ grinder with the sanding flappers in a 50-36 grit paper to cut into the metal.   I then prime the metal with a liquid based mix of the base coat so it’s loose with polymer and I brush it out onto the flashings. I then use fiberglass and resin to finish waterproofing the vertical legs of the wall to deck. See picture below for an example. Completely encasing the L flashing makes sense to me, it eliminates the possibility of water sitting at the wall and finding metal to attack.  I’m also seeing this detail in Pli-Dek and Duradeck’s details, and I hope to see other manufacturer’s follow suit if they haven’t already.

So what’s your thoughts? Comment below please.

IMG_20160127_095933089_HDR
Waterproofing the vertical leg with fiberglass & resin.
IMG_20160125_130154359
Prime all metal flashings before installing coating system! 
061ed-img_2061
Impossible to waterproof this termination! Deck waterproofing MUST extend up the vertical leg, behind the stucco paper.  
655 mulligan AG 004
A door is already in, the deck can’t be waterproofed correctly. The door must be removed for the flashing to be installed.

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