I am tiling my bathroom floor

[gareth jones]

Hello, my house is only 7 years ols and the floor creek like mad, i am going to put tiles in my bathroom for a new floor. i am told to put a 6mm mdf board down first and screw it down to the floor boards. is this thick enough or should i get 10mm mdf board.

cheers gareth

[pushkins]

No, No and No.
Never use MDF as a sub floor for tile...NEVER

First fix the creaks, you need to first screw down the existing floor to the floor joists, if you can see the nails in the existing floor then use these as a guide. Use screws NOT nails.

Then install 1/4" backer board, it's available at all big box hardware stores ( Lowes and Home Depot, approx. $10/ sheet 3x5) make sure you use the backer board screws with a square drive head ( $10 a box and 1 box does three sheets, they are green)
Make sure you screw the backerboard at all the indicated spots (it has small depressions where screws need to go)
The backerboard can be cut by scoring and breaking or if you have a masonary blade on your circular saw this will work well too.

For some added stability you can apply a (1/4" notched trowel) layer of tile thin set mortar under the backerboard directly on a clean sub floor, if you do it this way you can use 1 1/4" roofing nails instead of the backerboard screws.
Do not let the thin set applied under the backerboard dry before you nail or screw it down.
If you use thin set under the backerboard then let it dry 12 hours before tiling.

Good Luck

[Biddle34]

Curious question for pushkins

I didn't use a mortar under my bathroom floor, but used roofing nails to put down the backerboard. I did this in the fall of 2006 and have not had any problems since, what problems should I expect since I didn't do this according to your specs?

Also, how does a flooring company complete a tiled floor in two days? Based on your directions it would be a 3 day minimum job. Are you just being extra cautious or is this flooring company not performing quality work? Thanks!

[pushkins]

When you use roofing nails you can run the same risk of floor movement, roofing nails as well as all nails can come loose (just like on your roof), that's why it is always recommended to use a mortar bed under the backer board when using nails. Screws bind tight and do not come loose over time.

It doesn't mean you will have problems, if you have a stable sub floor you will be fine, if you don't, then there is always the possibility of movement in the sub floor then transferring to the backer board and then you will see cracks in the grout and or tiles.

It's easy to tile quickly if you have to:
Lay the backer board without a mud bed, tile with quick set tile glue and grout 4 hours later.
or
Lay the backer board with quick set mortar bed wait 4 hours (or start tiling after you lay the last sheet), tile with quick set and grout 4 hours later.
or (as I've seen done)
Lay the backer board, glue the tiles down and start grouting the next morning.

Like all work, just because someone cuts a corner doesn't mean there "will" be a problem, it just means there is a much higher chance of it happening.
A bag of mortar to use under the backer board is $12 and for the average home owner an extra day in drying time isn't as bad as pulling up tiles to redo a project.

I do many major bathroom and kitchen renovations a year, I am cautious, I don't like unhappy clients and I have never been asked to repair any work we have done, a bag of quick set is about $15 and we can be grouting 4 hours later.