Expert: Richard Taylor, AIA - 3/16/2010

Question
The framers who installed our balcony did not leave a slope causing water to pool next to door and wall and leaks through the balcony even though there is flashing against the wall and a layer of grace ice & shield on the deck to temporary protect the plywood subfloor.  We are planning to eventually finish it with tile.  How do we resolve the slope issue? And, what is the best way to waterproof before laying down tile? (With metal lath and concrete?)  Thanks.

Answer
Good evening Betty - thanks for your question!

Sorry about the leaking - that's a very frustrating situation that is easily avoided with proper construction techniques.

But it's reasonably easily fixed, also.

First things first - I assume this is a wood-framed balcony...that means it's probably not suitable for tile, regardless of the substrate you install.  Concrete is not waterproof anyway - it won't solve your leak problem.

Wood framing - especially an outdoor balcony - is probably far too flexible to install tile over.  The tile would crack and split very soon after installation.  So I'd consider some other surface, unless this balcony is built like a tank!

But back to the waterproofing!  You're right, you need a slope to drain.  Best way to do this is with "sleepers".  Sleepers are basically long wood wedges that sit on top of the existing framing to create a slope.  You don't need much - 1/8" per foot should do it. Another layer of plywood goes on top of the sleepers, then your waterproof membrane.

Whatever finish you put on top, you need a good single-ply membrane to waterproof the deck.  There are several types from neoprene to vinyl.  All attach similarly, and should be extended over the edge of the deck and up the wall as far as you can get it.

You can install just about anything on top of most of the membrane, but you need to be very careful that you don't puncture the membrane in the process.  Wood decking can go on top, but it has to "float" - you don't nail it in place over the membrane.

If your deck is built solidly enough for tile, then you'll be putting a mortar base on top of the membrane, just like building a shower.  Tile over the base, grout, seal, and you're done.

Either way, talk to a local design pro about this first, or at least contact a membrane supplier to discuss the details of proper installation.

Hope this helps!

Richard Taylor, AIA
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