Problem with newly tiled kitchen floor- advice?

[Pal]

I just completed ripping out my asbestos-based vinyl flooring and replaced it with ceramic floor tile. looks great!
However, I noticed I have a tile (or two) that have an edge slightly hgher than the others. Three days after completing the grouting, I noticed the grout cracking around one of the tiles with a raised corner. After closer inspection I noted some movement of the tile. Now what?

Should I scrape up the grout from around the tile, remove the tile and then re-cement it in place? I believe the movement is caused by a disparity in the level of the underlayent, maybe an 1/8th of an inch. I am pretty damn sure I screwed the underlayment down solidly. I used 3/4 inch exterior grade plywood for underlayment (over a 3/4 inch subfloor) and Versabond fortified thinset mortar which is polymer-modified. Is this inevitable given the raised corner, or can I level the tile using a thicker bed or mortar? Can I use mastic ? I have no clue how to resolve this.

Any assitance/advice is appreciated. All other tiles, even the other with a raised corner are adhereing fine, but I am only a few days in.

[tileguytodd]

A 1/4 " cement board backer would have been a better choice as an underlayment, however, given what you have remove the grout from around the tile, remove it by breaking it up with a hammer (if you try to pry it up from the side you will likely chip another and be replacing 2) Clean up the old thinset and grout very carefully from the other edges of tile and from floor using a small very sharp cold chisel or carbide tipped chisel..Then using a sharp wood chisel knock down (or shave down) any high spot.Reset with versabond, wait 24 hours and grout remembering to feather the grout into the existing.
Good Luck to you.
Next time, use a cement backer board for best results and increased lifespan of the installation

[Pal]

Would you put the cement backerboard directly over the subfloor, or should I have laid say 1/2 inch plywood then the cement board to equal the same height? I went with the 3/4 inch plywood because I could not remove the cabinets and the height of the new underelayment had to match the height of the remaining underlayment I could not remove (my circular saw could only cut to about 3 inchs from the cabinets). How elese should I have done this?

Also, is the failure likely due to the mortar(could it have been too dry..it was the last piece I laid from that batch) or more likely due to the high spot? In other words...was I wrong to assume that an 1/8 inch high spot was no big deal?

Thanks

[jadnashua]

First, I'm not a pro, nor have huge experience in tiling...whilte tiling over plywood directly with mortar then tile is possible and can last a long time, everything has to be perfect for it to last. Versabond is good for many things, but I'm not sure it is flexible enough to last directly on plywood in your case. When you put the tile back down, make sure you get 100% coverage - if it isn't flat, you may have to back butter the tile to account for the differences. If the lip was caused by there being a gap between the two layers of plywood, the flex when you step on that area will cause continued problems.

If there are any voids or gaps between the two layers of plywood, you can expect problems in the near future. My unprofessional opinion.

[Davy]

Yep, make sure the plywood has no movement when you take up the tile. Fix the movement or it will be doing the same thing again.