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Installing tile on exterior deck

JudsonC's picture

I am wanting to install tile on an exterior deck, I live in Kansas City (cold weather), the deck currently has composite decking. I have been told that I need to lay a layer of 3/4 inch ply and hardie backer over deck boards. What type of tile works best on exterior applications, thinset or mastic?



I've installed tile on two (post #207309, reply #1 of 4)

I've installed tile on two porches over 3/4" plywood decking, and both have held up well for 18 years. I used a compound mastic adhesive, simply because I feared flexing would cause cracking and detachment if I used ordinary thinset (that was a guess, not based on empirical experience). I grouted with standard grouting, but once again I mixed it with liquid latex rather than straight water, to provide added flexibility.

If memory serves, the mastic adhesive was made by Inax (probably 2nd biggest toilet maker here in Japan [first is Toto, of course]).



". . . and only the stump, or fishy part of him remained."

I would be afraid (post #207309, reply #2 of 4)

Hopefully someone here knows something about this subject and won't chastise you for not calling your supplier.

I am not a supplier nor an expert tile installer, but I personnally would be very afraid to put tile on a wood deck.  It seems to me all decks float to some degree with twisting and flexing.  Not a good thing for tile.  I would guess this varies by location.  Maybe warm southern CA could work, Montana?

It will be interest to see if anyone WHO KNOWS anything will respond.


tile over woodfloor (post #207309, reply #3 of 4)

We have used Schluter Ditra over 3/4" exterior plywood. Had no problem over 20 years.

double check on the John Bridges Tile Forum for the latest technology

a couple of things to consider: (post #207309, reply #4 of 4)

A lot of manufacturers nix their mastics being used for situations like horizontal applications on exterior decks. There are usually caveats for water exposure, etc. A true thinset would be your better choice.

Hardie used to be prohibited for exterior horizontal applications. Walls were okay. I'm not certain if changes to the board's composition over the past few years have changed that restriction or not. But a true cement board like Durock or Wonderboard might be more appropriate.

In general, you'll need a transition material between the existing deck boards and the cement board. Cement board manufacturers pretty much all restrict their materials from being installed directly to any plank material. So yes, a layer of plywood is appropriate over the existing deck boards and under the cement board.

There are tile-on membranes that can go right over the plywood. But in more demending wet/dry/freeze/thaw installation, most recommend cement board as a transition between the plywood and the membrane due to differential movement of the wood versus tile, and possible shearing action that could occur at the bonding layer of the tile.

So yup, typically a cement board is installed over the plywood.

Then you'll want a memebrane over the cement board. There are trowel-on membranes and sheet membranes, etc. Some are rated for exterior use, some are not. The two I use most often are Ditra and Nobeldeck. I prefer Nobeldeck for a few reasons.

Then thinset the tile down over the membrane.

You can certainly omit steps or use materials as they are not intended to be used in your application by the materials' manufacturer's. But that's always a crap shoot.

FWIW, for an outdoor balcony (about 230sqft), that I'll be tiling this spring, over the joists it'll be: two layers of plywood, then thinset and cement board, then thinset and nobeldeck, then thinset and tile.

There are 10 kinds of people in this world; those who understand binary and those who do not.