Ceramic over T&G planking

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Old 03-28-07, 11:10 AM
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Ceramic over T&G planking

I have a 1901 brick row house with joists between 12" and 16" o.c. There is 4" x 3/4" tounge and groove nailed to the joists which serves as the finished floor surface. In my kitchen however there are 2 layers of lenoleum and my cabinets were installed on top of the first layer. I am planning on removing the lenoleum, placing backerboard and ceramic tilings from there. I can not remove the T&G as that would entail me removing all of my base cabinets.

I have read the posts that discourage tiling over hardwood becuase of its movement. I do not think i will get the same kind of movement with this nailed T&G as i would if i had a finished hardwood over a subfloor.

Can i apply the backerboard to the T&G?
 
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Old 03-28-07, 01:04 PM
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No.

There IS movement in this T&G. You will have to lay down a suitable subfloor for the tile or the tile and grout WILL crack.

I recommend laying down 5/8" plywood over the T&G then the cement backerboard over that.
 
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Old 03-28-07, 01:09 PM
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What sort of movement are you concerned with? Vertical deflection or horzontal thermal type movement.
 
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Old 03-28-07, 01:45 PM
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The planking moves to much with seasonal changes and changes in moisture conditions. You need to do something to isolate that movement from the tile. The answer to that, is that you need to go over the planking with minimum 1/2" plywood (thicker would be better). The plywood is more stable than the planking and will not be affected as much by seasonal changes. You can use cbu or an isolation membrane over the plywood.
 
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Old 03-29-07, 11:03 AM
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Thanks for the info.

I definitely agree that the planks would see more seasonal movement than plywood. I have read to install an exterior grade plywood with a moisture membrane and then the mortar and tile. Should i use the recommended 6 to 8" oc fastening patterns for the plywood to the planking?

Additionally...If thermal movement is at play and since the plywood will now take any thermal forces from the planking, can I simply install a 1/2 backer board to the planking and eliminate the membrane? The backerboard won't be as stiff for deflections should be able to accomidate the thermal forces.
 
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Old 03-29-07, 12:23 PM
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Yes, use the 1/2" backer over the plywood without the membrane.

You just don't want your subfloor laying in the same direction as the T&G.

Also take into account the height of your appliances. Sometimes people forget about this and they tile up to the dishwasher, and then they cannot remove the dishwasher because of the height of the floor.
 
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Old 03-29-07, 03:54 PM
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Make sure all the planking is secured well to the floor joists. Use extra nails and screws as needed. Use 1/2" or thcker bc grade or better exterior plywood. The plywood should be installed perpendicular to the floor joists. Leave a small gap between the plywood sheets and around the edges of the room for expansion/contraction - dont butt the ply sheets. Screw the plywood into the planking every 8"in the field and every 6" around the edges. Avoid screwing the plywood into the floor joists. This will further isolated the movement of the joist structure from the tile above. You dont need 1/2" cbu. You can use 1/4" cbu over the plywood. The cbu gets bedded in unmodified thinset (dryset) using a 1/4" square notched trowel and screwed every 8" in the field and 6" at the edges. Again, avoid screwing into the floor joist as best you can. Leave a small gap between the sheets of cbu and around the perimeter of the room. You need to tape and mud the cbu joints with thinset and alkalai resistent mesh tape. Its best to do this while your setting the tile. If you do it before, you'll wind up with some high spots and it'll be difficult to get some of the tile on plane with each other.
 
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