QUESTIONHow 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?
ANSWERANSWER - 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 www.CTaSC.com 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.