I am trying to tile over an unlevel plywood floor


Old 10-21-12, 06:00 PM
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I am trying to tile over an unlevel plywood floor

I am a novice at tiling floors but I am willing to give it a try. I would like to tile my kitchen/dining room floor with 12x12 1/4" porcelain tile. I have 2 layers of 5/8" plywood for a total of 1 1/4". I have a low spot in the middle of one plywood sheet of about 1/8". A high joist that is about 1/8" high in the center of the next plywood sheet. There are probably other variations that I have not discovered. I also notice a slight decline toward a center wall. How is the best way for a novice to provide a level floor to start tiling? I was thinking about using 1/4" hardi backer board. Can I use the motar it sets in to level the floor? Or should I consider a floor leveling compound? If flc which one should I use to allow me to be able to screw the backer board down to the subfloor?

I could really use some help here.

Thank you
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Old 10-22-12, 07:44 PM
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Hi Lionsfanx, hey, me too.

You need to evaluate the entire floor for flatness, level would also be nice but flat is more important. Get a long straight edge, 8-10' is best. The floor needs to be "flat within 1/4" in 10' and 1/16" in 12" of the desired plane".

Depending on what you find you'll have several options. For sure you should try to knock down any high spots if minor, otherwise you'll have to raise the low spots.

Originally Posted by Lions fan
Can I use the motar (mortar) it sets in to level the floor?
No. That will do nothing to change the flatness of the floor.

If you use a tile backer board, patching/leveling is done after, not before. You could use Ditra membrane (instead) after you make the floor flat. It's a better method too.

Old 10-23-12, 02:02 PM
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Ask a buddy or significant other to give you a hand with this step. Rather than purchase a long straight edge (pricey), get some mason string. Have your partner stand at one end of the room and hold the string tight to the floor. You stretch a length of string to the other side of the room and slowly lower it to the floor keeping it as tight as you can. If the string touches the floor before you finish lowering the string, mark that as a high spot. If you lower your end of the string and you touch the floor before the middle does, you can make note of the low spots. If it touches completely and evenly, you have a level floor. Evaluate, measure distances off of level and give us an update.
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