Porcelain Tile on Raised Sunroom Floor?


Old 06-25-07, 08:20 AM
jdegeorge's Avatar
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Porcelain Tile on Raised Sunroom Floor?

We just had a sunroom added to our house. It's a 10' x 12' room built on a raised deck of pressure-treated, 16" OC 2" x 8" joists covered with 3/4" PTS underlayment plywood. The room is protected from all weather elements.

We'd like to put down a porcelain tile floor in this room but as sturdy as it is, there is still a little "give" at the plywood seams between the joists.

I've seen articles about putting down concrete backerboard so that the sub-floor is a total of 1-1/8" thick, or putting down a mortar bed (http://www.hometime.com/Howto/projects/ctile/tile_4.htm). Are these suggestions appropriate for our application?

How can this surface be prepped/made sturdy enough to support a porcelain tile floor?

Thanks in advance for your help!
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Old 06-25-07, 06:02 PM
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How much room do you have to come up higher? The reason i ask is because the Pressure treated ply may provide a lot of movement that cement board alone wont be able to handle. The usual type of ply to be used would be an exterior glue rated underlayment carrying a code of ACX or BCX. If it were me, I would put a 1/2" sheet of ACX fir plywood over the PTS to absorb the movement and help stiffen the floor between the joists. Screw it into the PTS but try to miss the joists. Leave a 1/8" gap between sheets and fill the gap with a cheap latex caulk. Then put a 1/4" cement board over the ply and set it in a combed bed of thinset using a 1/4" square notch trowel. Use 1 & 1/4" galvanized roofing nails to anchor the board to the plywood. Tape the seams of the cement board with thinset and fiberglass mesh tape. Start tiling the next day using a modified thinset.

Is there any mid-span support for those 2x8s?
Old 06-26-07, 09:20 PM
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Very good advice from Bob. Installing that PT plywood was not the right thing to do. In addition, you need to answer Bob's question concerning any mid-span supports, and what the max span is.

If the joists are running the 10 ft. way, you should be ok for ceramic or porcelain tiles? If they're going the 12 ft. way, you'll probably have too much deflection for a good tile installation.


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