remove subfloor before tile and backer?

[Colonel]

Hello again!
Im almost ready for tile but I wanted an opinion on something.

My bath has plywood floors over top a slatted floor (see pic)

Should I remove the plywood and attach my backer to the slatted wood or place the backer over the plywood?

Im thinking if I can remove the plywood sub floor , my new floor with backer and tile, will come flush with the hardwood floor at the entrance to the bath...any ideas?

still cant post pics yet but this link is for the pic

i29.photobucket.com/albums/c255/lastweeks/houses/subfloor2.jpg

[HayZee518]

I was thinking if the ply is firmly attached and there is no "give" in the floor, put the backer right on over the ply. bathrooms for some odd reason always get punky near the toilet.

[pushkins]

Yep, leave the ply down, strictly speaking backerboard wasn't designed to go directly over 1x 4,5,6" etc... material.
I always re screw down the ply (never use nails) not only to the 1x boards but also try to find the joists and screw everything down together. Then screw down you sheets of backerboard, don't scrimp on the screws here either, make sure you fill all mark spots.

If you wanted to maintain the hardwood floor height you could cut out the 1 x slats in the area leaving them under the walls and then install a 3/4" flooring like Advantech etc... then your backerboard.
The big thing here to watch here is often walls may have been built between joist voids, so you would need to watch that very carefully.

[CharlieO]

Ply wood is just as good a substrate as backer board, if you secure it properly.
Make sure it is well screwed down, into joist where possible.
Make sure the plywood is washed clean of dust, and slightly damp when you apply a Latex fortified thinset and you will be fine.
I have done 30- 40 baths this way and have no issues

[Colonel]

thanks for the responses

i think ill add hardie straight to the plywood as suggested

can i get away with 1/4" hardie? Ive been told that it should be 1/2" , but Ive been "told" a lot of things

[pushkins]

1/4" is all you need and in 99.9% of cases all you would ever need for floor tile, 1/2" is usually used on counter tops or wall situations. Use the Hardi backerboard screws (square drive) to screw it down, (I see so many people use drywall screws )
If you have a little height to play with, mix up some thinset (cheapest you can find) and spread a layer over the ply, trowel out with a 1/4" trowel. lay the backer board onto the thinset and screw it down.

[Colonel]

thanks for the good advice!