I am in the middle of a bathroom remodel. I put down 1/2" plywood for my subfloor and am now thinking I should have used 3/4". I am finished framing the shower so I do not want to rip anything out at this point. My original plan was to put 1/4" cement board over the plywood and then ceramic tile. Is 1/2" as the subfloor enough? Should I add another layer of plywood, 1/4" or even 1/2" over the existing 1/2"? I was thinking of putting down 1/2" cement board instead of the 1/4", would that suffice?

Same goes for the shower. Since I will not be using cement board would a thicker mortar bed do the trick there?

Thanks

You should have used 3/4 first with glue and screws. I would put 1/2 ply down on top of exsisting with the grain with the wood grain running oppisite of your exsisting 1/2 ply. Before laying it down be sure to put some wood glue between ply and then screw thruogh both sheets countersunk to joices. Good luck

Yes, follow the above instructions... I would go as far as saying use 3/4 over the 1/2.
Using a thicker mortar bedding will do nothing for your support. You will need to add there as well. I use nothing less than 1/2 inch cement board.
Mike

I think the answer is somewhere in the middle here. Yes you should have started with at least 3/4" ply. Normally your Hardibacker for floors is 1/4" but 1/2" set in modified thinset will greatly increase the floor strength. Howvever, I would not take the chance since another mistake would be very difficult to correct. Put down another 1'2" glued and screwed. Then come back with the 1/2" Hardibacker. Hope you come back for more help when you go to set your toilet, we'll be here.

Thanks for the comments. My toilet happens to be wall hung so I should be OK there.

Hi Guys:

Thinking 1/2" plywood should have been 5/8" plywood minimum. Hardibacker states that they require a 5/8" plywood between 1/4" thick modified thinset mortar and their hardibacker.

James Hardie: HardieBacker 1/2'' backerboard

I am not sure this is helpful... but I would add 1/4" exterior grade plywood to 1/2" plywood (against grain)... and I would use rosin paper between plywood, not glue/adhesive (creates bellies)... OR AM I BEING OLD FASHIONED...? Then set 1/2" hardibacker in 1/4" modified thinset mortar (screw with hardibacker screws and tape joints appropriately).

I think a lot also depends on transition into the hall or other room at dooway. A marble threshold will hide much of this... if hall/other room finished floor height works with this..?

I am suggesting how I do things... but I am also asking how YOU GUYS do things... let me know.. always looking to learn.

Mark

The two 1/2' sheet of ply add up to more than one 5/8" so I feel they should work with a 1/4" Hardibacker but I suggested 1/2" just to be certain. Two sheets of 1/2" are not as strong as one sheet or 1". Mr. Hardie must be a rich man based on how much of his stuff I buy. If you read my posts often you will see I really do like Hardibacker and Hardiplank. Funny thing, a 1/4' sheet cost $7.58 and a 1/2" piece cost $7.68, twice the thickness for a dime more.

I have to wonder how much hands on work some people giving advise have... I get headaches trying to figure out some of these answeres... There are codes and such things as right and wrong. I often wonder where people get some of there info.
Mike

Hey Bob.. did not see you advise the additional 1/2" plywood...all I saw was "put down another 1'2" glued and screwed".. kept reading and just thought you were suggesting OK for 1/2" hardi. over the 1/2" plywood. (Notice I also suggested 1/2" hardibacker (in 1/4" modified thinset)).

Tell me... do you still use rosin paper in between layers of plywood.. Or is it all "glue and screw" today.. I learned to glue and screw 1st layer plywood to joists... then rosin paper, then screw 2nd layer of plywood (into joists)... then install 1/4" modified thinset, then 1/4" or 1/2" hardibacker (or durock) screwed every 6 inches.

That is how I do it, Bob. My last post asked a question... so far not sure anyone read it... "I am suggesting how I do things...but I am also asking how YOU GUYS do things....let me know..always interested in seeing how others do things".

Let me know, Bob... just curious... Mark

And who is Mike the 1UNV talking too..

Rosin is great between a sub floor and a tongue and grove hardword but not needed for the two 1/2" sheets of ply. Screw and glue and you are good to go, there will be no movement to cause squeeks, thats what rosin removes, squeeks. Not sure exactly what the iunv is talking about but its is the James hardie Company that created the installation spec. If code says 1/2" and Hardie says 3/4" you need to go with Hardie, always stronger and never weaker than what the manufacturer specifies. IBC doesn't get too specific when it comes to remodeling and adding a tile floor.

Oh My... I wasn't sure what I was saying for a second myself... that answere was spose to be in another post... I was talking about the guy who said he was told he should sheetrock his entire house with cement board. I'm not sure sure how I got that post in here... I had to have flipped over and forgot... dang phone calls. Sorry!
Mike

The cement board guy should not listen to his friend. What a crazy idea.