How do I install Tile on upper Exterior Patio Deck over a room?


How do I install Tile on an upper Exterior Patio Deck over a room? - I plan on installing tile over an outside deck with a wood subfloor. Do i need to have a Roofing Company to apply asphalt, and than do i apply to coats of permabase, to make sure the room undernith the deck doesn't get water infriltration?


ANSWER - Exterior decks are very problematic if they are not installed correctly, particularly if there is occupied space underneath it.

There are several steps necessary to make sure your tile deck will perform as intended.  First, you need to make sure it is structurally sound to be able to take the weight and that it will not cause too much deflection.  Make sure it is IRC compliant by having a structural engineer inspect it.

Next you need to determine how the water will drain off the deck.  Will you install a drain or will you have it run off the edge into a gutter?

Next you need to create a pre-slope substrate by applying a concrete bed with a slope to drain.  Then you properly apply a roofing membrane such as hot mop asphalt coating or apply a sheet waterproof membrane.  Then you should apply a mortar bed over the membrane or there are membranes that you can bond the tile directly to it if it is appropriate to eliminate the top mortar bed.  If you apply the mortar bed then apply a secondary waterproof membrane over it of the type that allows you to bond the tile directly to the membrane.  Be sure to do at least a 48 hour water test to make sure it doesn't leak.

You mention Permabase which is a cementitious backer board.  it is possible to use a backer board rather than a mortar bed, but it would be difficult to achieve an adequate slope on its surface.

Make sure you have movement joints (expansion joints) placed within the tile assembly every 8 to 12 feet.  Make sure you have perimeter movement joints filled with a proper ASTM C920 sealant (caulking).  Make sure the tile is installed achieving 95% full thin-set contact between the tile and its substrate.

It is important to provide quality control inspections to make sure the installers follow industry standards and manufacturer's installation directions for each component of the installation.  If it is afordable you should hire a consultant like ourselves to write the installation specifications, provide a quality control plan, and to perform quality control inspections.  If it isn't affordable then go to our website at to Expert Answers and under Resources and print a copy of the Quality Control Installation Guidelines we provide at no charge as a industry community service.

Good luck.

4 thoughts on “How do I install Tile on upper Exterior Patio Deck over a room?

  1. Phil Perez says:

    I have a Hot Mop with Roofer sheeting melted into the top of it. It has three-quarter inch tongue and groove then a Hot Mop and then roof sheeting. I want to tile over the entire deck it’s 960 ft.² do I install a mud bed first over the surface and then thin set or do I install a membrane? How do you stick the membrane to the mud bed with out using screws or nails ?

    • Donato Pompo says:

      Hot Mop if done correctly is a good waterproof membrane. The hot mop surface should be sloped 1/4″ per foot towards the drain. The hop mop should flash up the sides of the perimeter walls at least 3″ to make it water tight.

      Once the hot mop is properly prepared then you can install a wire reinforced mortar bed over a 15lb felt cleavage membrane. The mortar bed should be at least 1.25″ thick with the 2×2 reinforcement wire embed within the bottom or top third of the thickness of the mortar bed.

      If the hot mop is properly sloped then the surface of the mortar bed should be a reflection of that and be properly slopped.

      If the hot mop isn’t properly sloped and it is too much work to fix it, you could apply a liquid applied waterproof/crack isolation membrane over the mortar bed and then bond the tile to it. Here again you have to flash it up the adjacent walls and install a base over it to cover it.

      Even if the hot mop is sloped you might want to apply the liquid applied membrane over the mortar bed to keep the water out of the mortar bed and help prevent efflorescence staining.

      If you use a sheet membrane you can’t penetrate it with nails or screws. You have to use a tile membrane where you adhere it to the mortar bed.

  2. Sep Golboo says:

    Hi Mr donation,
    I have a balcony about 200 square feet that was just hot moped . If I use mesh wire it needs to be nailed down to hotmop which damages the membrane , if I don’t nail it down mortar or cement will not stick to hot mop, hence I don’t know what next step is

    • Donato Pompo says:

      Hot mop waterproofing is a very robust method of waterproofing shower pans or balconies. Industry standards shows that this type of installation should have a non-bonded mortar bed so you don’t penetrate the primary waterproof membrane. The mortar bed should be at least 1″ thick and suspended within the mortar bed is a 2×2 inch 16/16 galvanized or stainless steel wire mesh that meets ANSI A108.02.3.7 should be applied over the pre-sloped hot mop surface.

      You should have flashed the hot mop up the wall at least 3″ above the finished surface. If you put metal lath on the wall over the hot mop, you can pre-drill the holes and fill with an ASTM C920 sealant (caulking) prior to screwing in the fasteners to make the penetrations watertight.

      We would normally then apply a liquid applied waterproof/crack isolation membrane over the mortar bed and then bond the tile to the membrane so we can keep the moisture out of the mortar bed and provide added waterproof protection.

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