Flooring Tile - Removed vinyl floor, now questions

Hi all, first time poster. I just got done tearing up the vinyl floor in our upstairs bathroom. It was very hard to pull up from the floor, and it delaminated in many spots. Underneath I found what looks like a 1/4" subfloor, looks like a cheap panel-type material (cheaply built home I'm sure). The house was built in '99 if that's any help. From what I read on this forum, I'm going to want to remove that, or keep it in there and thinset the hardboard over that, or should I remove the cheap subfloor and put 1/4" hardboard over the plywood that is underneath the current subfloor. I'm guessing the plywood is 3/4". Thanks.

the 1/4" plywood that your probably looking at can stay if you can get it fairly clean(not spotless, thinset will fill minor voids or cover small amounts of glue remaining from vinyl), if you start removing that(the 1/4" ply) you may very well find that IT is glued in also, so you would be in the same spot your in now but alot of work later, and 1/4" of subfloor less, put the hardiboard over that and tile away.

Yeah, there are no screws so that 1/4" plywood is probably glued down. It pulls up in the one corner, but in most areas it feels pretty well attached. I'm sure if I start prying it up it will pull apart and be a real mess. I guess I was more worried about the stack-up height of all the subflooring. With another 1/4" hardiboard and then the tile on top of that the floor will be up another 1/2" from where it already is. The glue and paper from the vinyl floor is a pain to scrape from the subfloor, but I guess that's about the only option.

¼" Hardie on floors is not recommended. It is made for counter tops. ½" Hardie or any CBU is for floors that will have to support a lot more weight then a countertop.

Have you checked the subfloors flex? L/360 is the spec. You may need another ½" of plywood, on top of the ¾" to bring the subfloor up to deflection ratings before the ½" Hardie is installed using thinset under it, before you fasten it down. Don't lay it on the floor dry!! It too must set in thinset mortar.

So with the thinset and the 1/2" + 1/2" + 3/4" plus the tile on top of that, it would bring it well over 2"!!?? Is that the standard? If I did that I'd need a toilet drain extension almost 2" tall, maybe more. If that's the way it needs to be then that's the way, but I was hoping that I could just use at most 1/2" of hardiboard on top of the 1" plywood. The 1/4" plywood that is on top of the floor already makes it pretty stiff. Let me know what you all think.

I just stopped down at home depot, and they have a display for their lifetime warranty. It states that you need bigger than 5/8" plywood, and 1/2" hardiboard, and that is all, underneath the tile(with thinset of course). With so many opinions I'm getting kind of confused. I don't want to go overboard, but I also don't want it to move and crack.

I inspect more Home Depot installs then any other failure inspections I do. Cha-ching! Keep on preaching misinformation Home Depot! It's like job security for us flooring failure analysist.

Those guys don't have a clue as to what is spec.

Is that 5/8 over 12 inch 16 inch or 19 inch center floor joists?
Will they ever get a clue?

You might want to check with Dave Gobis @ The Ceramic Tile Council of America! They make the standards!!
http://www.tileschool.org/