I'm not Bill or Mongo, but can tell you that NO, what you currently have and what you are suggesting are not acceptable. What is the tongue and groove you are talking about - plywood? boards? what?

1. Hardiboard MUST be set in thinset, not just screwed down.
2. Hardi is dimensional, not structural, so you absolutely must ensure first off that your floor is strong enough. Floors bend, tile does not - weak floor = cracked tile.
3. Regardless, you will need more plywood over your subfloor.
4. At the very, very least, I would remove vinyl and 1/2" ply and replace with 3/4 ply, then use Ditra if you are concerned about height. However, if the tongue and groove you are talking about is lumber rather than plywood, you may need to do something else.

How far apart are your floor joists? What size are they? How large is the area you will be tiling?

Steve,

As you know by commenting on it, and as Alice already mentioned, you want thinset under the hardie.

If you want to match elevations, your best bet would be to strip the floor down to the diagonal planking and use a membrane like Ditra. Any straight combination of planking/ply/hardie will set you high.

You can't Ditra directly over dimensional lumber (the diagonal planking). If you can strip the vinyl and clean up the 1/2" ply surface well enough to thinset the Ditra to that, your floor thickness will be about 3/4 +1/2+ 1/8+ 1/4 = 1-5/8" high, just a bit above your planking plus hardwood thickness.

If you wanted to match then perfectly AND most likely get better bonding results, you can strip the floor to the planking, add new 3/8" ply underlayment over the planking, then Ditra and tile. Depending on the tile you choose that could be a perfect match elevation wise.

It depends on how much labor and new materials you can put into the job.

Best, Mongo

NO, what you currently have and what you are suggesting are not acceptable.

YA THINK????

The floor will be strong enough, by way of the planking. The problem is the vinyl over the plywood. Considering your specific predicament, my suggestion would be to remove the 1/2" plywood, and replace it with 3/8", and then install Ditra over the plywood. You'll lose the thickness of the vinyl, as well as the thickness of the cement board. You'll still be a hair above the level of the hardwood, but not anywhere CLOSE to a 1/2". More like about 3/16", and for that a small wood reducer strip to match your hardwood would do the trick.

The 3/4" planking gives you plenty of strength in the floor. The problem is that dimensional lumber (the planking) tends to expand and contract way too much with the changing of the seasons (and even the humidity level). That's the reason for needing the plywood between the planking and the Ditra.

Thanks everyone for the advise...I am going to do it right. I knew just screwing down the hardie board was not correct.

I will remove the vinyl and old subfloor.

I figured the tongue and groove floor was strong enough but would not have thought about putting the 3/8 down.

I will put the 3/8 down and then ditra over that.

Now is ditra easy to install?

Based on what I have read I put the ditra down using un-modified thin set.

Then I am assuming I need to let that dry and then us modified thin set to bond the tile to the ditra.

BTW I bought some rectified tile from HD for the floor. They were made in China. These were special order and actually look nice but the porcelain is a little strange.

Thanks again,
Steve

You have it backwards, Steve. You use MODIFIED thinset to bond Ditra to plywood, then UNMODIFIED thinset to bond tile to Ditra. Ditra instructions state that you can tile immediately after installing the Ditra, but I have always waited.

Ditra is VERY easy to install. But just to clarify-- especially over plywood, you want to use as strong a modified thinset as you can find to bond to the wood! What I'll usually use is Laticrete's 333 liquid latex mixed full strength with their 317 thinset, and then for tiling OVER the Ditra, THAT'S where you use the unmodified, so I'll use that same 317 mixed with water.

"Based on what I have read I put the ditra down using un-modified thin set. Then I am assuming I need to let that dry and then us modified thin set to bond the tile to the ditra."

Flip those comments.

Use modified thinset to bond the Ditra to the plywood. Then use unmodified to set the tile on the Ditra.

The following is technique. My way. I'll spread the thinset on the plywood using the flat side of the trowel to key it into the plywood. Then I'll flip the trowel and use the notched side to leave a measured amount on the plywood.

Roll out the Ditra and embed it in the thinset.

I recommend since this is your first time you then peel back the Ditra a bit and take a look at the coverage on the bottom of the Ditra. Make sure you're getting good coverage, not spotty.

If you work too slowly, the thinset can skin over and not fully cover the Ditra.

When I tile over Ditra I use the flat side of the trowel to work the unmodified thinset into the waffle grid of the Ditra. Then I'll again flip the trowel and comb it out with the notched side to leave a measured amount on the Ditra.

Then set the tile.

Then drink beer.

Hah! I started writing my reply then had to stop and send out a couple of faxes. When I came back to finish the post I thought "hmm, I should check before posting, someone else probably already replied...". But I didn't. I posted anyway.

And thanks to Bill for expounding, I didn't write about that part. But I'm in full agreement with Bill. If I thinset over wood, I'll use modified, but I'll modify dryset with admix myself instead of using bagged modified.

OK...thank you all for the correction. I am also going to watch a you tube video of how to install prior to doing it.

I am going to attempt this on Saturday.

What size trowels should I use to bond the ditra to the plywood and to bond the tile to the ditra?

Also, when I place the tiles on the ditra do they end up laying directly on the top of the grid? Does this help to eliminate lippage (not sure how to spell)?

I have tiled floors before but have not used ditra.

PS I am assuming no screws or nails through the ditra are necessary.

Oh...and I am probably going to have to use what is available at HD or Lowes. It seems like the good stuff you guys recommend is hard to come by here in Southern NJ. Not sure why.

Thanks again,
Steve

Although they'll tell you to use a 3/16" v-notch to install the Ditra, I don't think it puts down enough thinset. I use a 1/4x1/4 square notch. As for what notch to use on the tile, I'd have to know the size of the tile, first.

Also, when I place the tiles on the ditra do they end up laying directly on the top of the grid? Does this help to eliminate lippage (not sure how to spell)?

Not quite. Usually the thinset will lift the tiles about 1/16" off the face of the Ditra. As for lippage, that's YOUR responsibility. :-) You know what they say-- nothing worth anything is easy! :-)

PS I am assuming no screws or nails through the ditra are necessary.

Correct.

If you go to Lowes, You'll find one of two manufacturers for thinset and grout-- either Mapei or Laticrete. If it's Laticrete, they change the names of all their products for Lowes. You want the Mega-Bond thinset, and the latex thinset additive. If it's Mapei, you want Kerabond (or Keraflor) thinset, and Keralastic additive. At Home Depot, it's Custom Blend thinset and their latex thinset additive.

Cool...thanks all. I am going to hopefully get most of this done this weekend.

Get the floor ready for tile on Saturday and start tiling on Sunday. It is only 50 sq ft of tile and I am keeping the pattern simple even though I want diagonal.

My wife thinks I should make this as easy as possible since we went a little over board with the tub surround with the niche, tile patter, corner shelves. Tub surround is not perfect but looks very good. Will be putting up picture next weekend or the project.

Thanks,
Steve

Did not get too far this weekend. One of my concerns was going to be if the 3/4" subfloor was under the tub. Well I ripped it up and then got to the tub and it was. So, I went to HD and bought a dremel multi-max and but it right to the edge of the tub.

Then I cut out the new 3/8" subfloor and that is ready to be screwed down.

But I am going to make sure the tongue and groove is level and structurally sound before screwing down the new subfloor.

I have the ditra and got the thin set and additive from Lowes. Hopefully, I will screw down the subfloor during the week so I can knock this out next weekend.

Thanks again,
Steve

Steve, as my good friend Rosanne Rosannadanna used to say...

"It's always something."

New construction takes twice as long as you expect. Remodeling takes four times as long. There's always another can of worms to be opened.

No doubt. Plus I like to take my time and not get stressed about the work I am doing in our newer house.

Based on the ditra video it looks like you can install the tile over the ditra w/o waiting for the thin-set to bond it to the plywood. Is that true?

How long should I wait to walk on the floor?

Once I can walk on the floor I will then grout my tub surround and floor.

Then I have to install the toilet and vanity.

Should I wait for the grout to dry prior to installing the toilet and vanity? If so, how long should I wait?

Thanks,
Steve

Yes, you can Ditra and tile the same day.

I'll tile, then grout the next day. I usually wait 72 hours before then working in the room (moving in fixtures, etc), but that's just me. A lot of people do it the next day.

I have another problem...when I removed the 3/4 subfloor from the tongue and groove.

I noticed the tongue and groove is pretty uneven. I believe some of the floor joist might be uneven.

Should I try and level this out with tar paper or roofing shingles prior to putting the 3/8 subfloor down?

I had to do this on a project previously prior to installing a wood floor.

I would like to have as even a floor as possible once the ditra is down. I dont want to have to try and make tiles level by using extra thinset here and there.

Steve

I dont think my ditra adhered well to the subfloor. In the main part of the bathroom it may be good enough. There are no loose spots.

But I had a feeling the closet was not adhered well enough or maybe it was...so I grabbed a corner and pulled on it. It pulled up with little effort.

Should the ditra be able to pull up that easy. Since this is the close I am going to screw it down. I know this is not what you are suppose to do with ditra but I do not feel like re-thinsetting it down. In order to make it even with the main floor I would have to remove the thinset and then redo.

The main area is secure w/o air pockets or gaps between the ditra and subfloor. But I am pretty confident that I could rip it up by pulling on it. Some areas were adhering well when I checked for adhesion but other were not. We probably did not make the thinset fluid enough.

How strong should the adhesion between the ditra and the subfloor be?

Is it good enough in the main area if it is adhered and there are no air pockets?

This is how the closet was but I had a feeling that it did not adhere to the backing because when I thinsetted that area it seems a little drier than I would have liked.

Thanks,
Steve

Once dry, it should be pretty set. Pulling it up should involve delaminating the felt backing in some way, it shouldn't cleanly separate from the thinset.

You may risk cracking tiles and grout if it's loose.

See if the boys stop in and comment....

Being that it's the closet, I wouldn't worry too awful much. But if you find the same thing out in the room itself, You might want to cut that part of the Ditra out, scrape the thinset, and redo it. Using screws, and you're going to see cracking grout. I can promise you.

That is what I thought.

Everything was going good until we mixed the thinset. We mixed the thinset as per the instruction on the thinset. I wish I had read the ditra instructions where it stated on bag can be used to cover 150-200 sq ft of ditra to subfloor and one bag to bond 50 sq ft of tile to the ditra.

Obviously we mixed it too thick and then the thinset went on this as well. My wife did add more liquid as we were realizing that it was too thick.

We are just going to go forward with installing the tile on the ditra. It looks good and I know that when I was applying the ditra the thinset was getting decent coverage.

We did set 16 tiles on Sunday and I walked on them yesterday and they seem very well fixed in place. No movement at all.

How level do the tiles need to be under the vanity? This is a 48 inch vanity with 4 legs. I know it would be best to make sure it is level. The subfloor was leveled out prior to installing with some shingles and tar paper but all is still not perfect and I am not the best at adding/removing thinset to make each tile level with the surrounding ones. It is coming out good but nothing is perfect.

OH...if things crack...we were planning on renovating the kitchen in three years so we will redo the floor and vanity at that time. Hopefully it wont crack but not the end of the world...we are only talking about 50 sq ft of tile.

Thanks,
Steve