Is my floor tile going to crack?

Use a 1/2" towel rather than the 3/8". Float your thinset mortar in high/low areas around toilet flange so that you have a good stick. Let the tiles sit in place for 72 hours before setting the toilet. 72 hours is 80% cure. Do not over tighten the toilet bolts when setting the toilet. You have done everything correctly so far. A ceramic tile floor on a conventional foundation/floor should not deflect more than 5% of the span. If your flange ends up low use a double wax ring. If you high/lows are more than 1/2 inch, consider 45 degree cuts in tiles that meet the corners of toilet. It is not uncommon to have problem areas around toilet flanges.

Hello decking. I am going to say this against all the other answers. If floor tiles are put down on a wooden floor they should not crack. Quarry type tiles are incredibly strong. I think that although the work may have been not well done but also the tiles were not up to it. There is no reason why you can't put quarry tiles down on a wooden floor and they won't last forever. Investigate the quality of the tiles. BB

Tile is much less likely to crack or loosen when laid over a properly installed wood deck. The other guy is correct in saying that a mud bed is the best way to go, given your situation. However, it may also be expensive if you are hiring a flooring contractor. A mud bed is not exactly a DIY project, and is subject to failure if you don't know what you are doing. If you want to ensure that your tiles don't crack, my advice would be for you to double up on your plywood. That is, two layers of 5/8" plywood, not OSB but 5 ply plywood. This will prevent your deck from flexing excessively. As far as Hardiboard, it is not necessary at all. It accomplishes nothing in your case. Both Home Depot and Lowes sell medium bed mortar that is approved for plywood, as long as the plywood is properly installed and doubled. As far as your toilet being lower, medium bed mortar can go up to 1” thick. So if the low spot is less than 1 inch, you are good to go. The mortar bed will cover it.

chances are that in a home as old as yours the floor joists near the toilet have been compromised by the plumber.

he probably cut into the joists to accommodate various drain pipes etc. this would result in sagging floors.

or the foundation of the house has sunk resulting in sagging joists and a sagging floor

once the floor starts to sag water on the floor may migrate into the joist area an rot can occur.

tiles will crack if the floor moves more that 1/360 of it's joist span. this is called the ME of the span. if you are not sure ask the advice of an arcetectual technologist.

the long anser is... you must repair the damaged joists before proceeding as there is no quick fix for this.

Your tile probably won't crack but may depending on how un-level it is. The problem I think you may have is when you go to install the toilet it will be unlevel. The toilet needs to sit level or it will look funny.

I do know you can get some sort of mortar mix with water and spread it over floor instead of using the Hardibacker. That way you can use that to make it level. You can put it on thick and thin to help make it level.

Hope that helps.

It is extremely likely that a year from now you will be re-doing this project because of cracked tiles.

If you must use 12x12 tiles, you will need to "float" thinset mortar to level this up.

This is why you usually see mosaic tile in old Victorian houses. If you go to tiles that are no more then 1"x1" you should get a lifetime out of them.

the fact that you are talking about a hardibacker board ..tells me you are in the states ..im a builder in the uk..but this applies wherever you are ...first the plywood should be screwed very securely ...we would screw every 6" ..we do not usually use any other boards ...however when you lay the tiles ..the tile size is not important you must use a flexible adhesive and grout ..or they will seperate with the wood expansion ...to make the adhesive flexible you can buy a product over here you can add to normal adhesive and grout ...its a white liquid ...not pva

You should be ok as long as long as the hardback board is flat and the floor doesn't flex or move. Just being unlevel won't make it crack, but could cause problems with water pooling etc.

did you notice that your 130yr old floor wasn't built with things like plywood, glue or backerboard? notice how the demo wasn't easy? when you're done with your new install, i could come in and demo it lickity split now that you're doing such a temporary job. the wise craftsmen who laid your original floor used a solid mudbed to level the floor and provide a proper base. this is exactly why things like backerboard simply don't work. plus we don't think things take skills anymore but you're about to find out just how wrong you are. please don't say you're using home depot indian slate either. that slate is the worst on the planet along with all the rest of the stuff they sell. you'll find out, don't say you weren't warned.

Before you install the Hardibacker, use a floor leveling compound. It's fairly easy to use and you'll have good results. It's available at big box home centers and most hardware stores. Here's a link: http://www.ehow.com/how_5628100_use-self-leveling-...