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Expert Answers
How do I prepare my outdoor patio for a tile installation?
QUESTION
How do I prepare my outdoor patio for a tile installation? - I am looking into tiling over an outdoor patio slab which is enclosed and not vulnerable to any weather problems. It has diagonal saw cuts throughout the floor, all of which have been grouted. It also has a 6 x 13 stamped concrete area that has saw cuts and an arched joint into it as well. I am looking to install 6 x 24 wood planking tile over it and I was wondering if I fill the joints with SikaFlex Caulk, and redgard the saw cuts. would I run into problems if I use a membrane over the floor before installation? The floor has been there for over 7 years now, only a few small crack throughout. I was going to use a membrane roll over those areas. Is that the way to go? And should I Place Joints throughout the floor and caulk them every 6-8 feet?ANSWER
ANSWER - To install tile on your outdoor covered patio you need to consider several things. Are you in a freeze-thaw climate area? If so you need a tile that is freeze thaw resistant. If you are using a ink jet glazed porcelain tile then it should be. Will you get windblown rain that will cause the floor to become wet? If so you need a slip resistant tile. Is the concrete slab have any contaminates on it or is it porous enough that readily allows water to absorb in it? If necessary, scarify the slab to remove contaminates and to open the pores of the concrete so the tile products will bond well to it. Do you have a vapor retarder under your patio that comes up along the side of the slab and footings that prevents the migration of water and moisture? If not, and the grading is such that water can collect under or adjacent to the slab, then you could develop a moisture vapor transmission problem that can result into efflorescence and staining. Ceramic tile is relatively resistant to moisture vapor, but it has limitations. There are epoxy coatings that can be applied to the slabs to limit moisture vapor, as long as you don't have a hydrostatic condition (water from a higher level traveling to under the slab causing pressure). You can install trench drains along the perimeter of the patio to divert moisture away from slab.Regarding the saw cuts and cracks in the concrete floor, technically all control joints are to extend up through the tile and expansion joints have to continue thought the tile work. Obviously that wouldn't look too good in your case. Some Tile Installation manufacturers will allow their crack isolation membranes to cover control joints and cracks, but not expansion joints, as long as they are not structural movement joints or cracks. That means they cannot move vertically, but they can move horizontally with limitations.
Assuming you have a properly installed vapor barrier, that the saw cut joints and cracks are not structural and don't exceed the width limitations of the membrane, and that the slab has adequate expansion joints installed within it that have to continue through the tile work. Some membrane manufacturers will recommend properly scarifying the concrete slab. Filling the cracks and saw cut joints with a high performance polymer modified thin-set mortar that meets ANSI A118.15. Then properly applying the approved crack isolation membrane over the slab, and then adhering the tile with a high performance polymer modified thin-set mortar that meets ANSI A118.15. Install generic movement joints every 8 to 12 feet in each direction, and at all perimeters and changes of planes, with an ASTM C920 traffic grade sealant with a minimum Shore A hardness of 35 so high heels can't penetrate the sealant. Use a primer if required and a polyethylene backer tape at the bottom of the movement joint if the tile isn't too thin to do so, but make sure you follow the sealant manufacturer's instructions. Use a cementitious grout that is made by the same manufacturer as the adhesive and make sure it qualifies for their 10 year labor and material warranty. You can seal the grout with a penetrating sealer that is approved for your type of application that will make the grout more stain resistant and easier to maintain. Of course follow all of the industry standards and the various manufacturer's directions to ensure the preparation and tile is done correctly, which is typically a requirement of the labor and material warranties. Good Luck!
