You have a plank subfloor below the ply and Ditra above. It's really not a problem. March onward!

I don't see a mention of the plywood being over plank that mongoct refers to in their post.

Why are you concerned about the glue in the first place? What causes you to question it?

For tile, especially stone/porcelain, you need 2 layers of plywood. The 3/4 being glued and screwed is perfectly fine and good IMHO. You should be adding another layer of 5/8" plywood on top of the 3/4". The top layer should be screwed to the 3/4, but not through it. Use 1" screws or there abouts.

I'm no pro, so don't take my word as gospel. But, I did have 3/4" plywood glued and screwed to 100 year old floor joists. Then I added a special thin birch plywood (3/8" as strong/stiff as 5/8) screwed as I mentioned to the 3/4.

On top of that I laid Nuheat heating cables in thinset. Then Ditra, then white 12x12 marble tiles. 5 years on no concerns, and this is on a 2nd floor where the joists span about 15 feet (beyond what they should but they're try 2 x 8 100 year old lumber) and have a laundry room vibrating right next to the bathroom.

I go beyond deflection specifications, especially for natural stone, but I've had zero issues.

I don't see a mention of the plywood being over plank that mongoct refers to in their post.

I could certainly be mistaken, but I believe it's from a previous post. In this case, the 1" planking is the subfloor, the 3/4" ply the underlayment.

Why are you concerned about the glue in the first place? What causes you to question it?

In general, you don't glue and screw the underlayment to the subfloor. Just screws. No glue.

Mongo & TorontoTim, thanks. Mongo you're right about the diagonals and plywood. 1x subfloor and we laid 3/4 ply over this for the underlayment. When I mentioned exterior plywood I mean exterior glue yellow pine non treated plywood. The room is 110x103", so not very big.

First, there is the 1x6 diagonal boards from the 20's, nailed down to the joist. I'll call this the subfloor for now. The house has been very stable over the years. We took out the fir T&G finished flooring because it had some water damage in spots from the sink and shower area. The diagonals are just fine.

Second, the 3/4 plywood is a a GP product CALLED "23/32 CAT PLUS STRUD-I-FLOOR TONGUE & GROVE" . I'll call this the underlayment. This product is glued with construction adhesive, using a caulking gun, to the 1x6 diagonal subfloor and then screwed down 6" oc.

Third, I read an article called "Position of Underlayment to Prevent Cracked Tile and Grout" It was linked on a thread in the JB forum. It mentions the positioning of the butt joints of the plywood being critical. They recommend to have them joined, 1/4 of the span, away from the joist. So in my case, off the joist by 4". My plywood was butted on the joist.

Fourth, the expansion gaps are probably too small and are non existent at the periphery. The picture below shows one of the larger joints. It also shows the area depth yet to be fitted.

I have posted on the JB forum last night and I got some feedback from them this morning but haven't responded there yet. on the JB forum, the question came up about pre-drilling for the screws to prevent "screw jacking". I think the pre-drilling is to insure the ply is sucked down tight to the boards below. While there wasn't pre-drilling, I believe it is screwed down tight. The carpenter did a nice and tight job with the laying down of this floor. It feels stiff. The JB forum questioned about the glue and an explanation was given. It is an issue of small voids being created under the ply where the bead of glue makes contact, yet holds the unglued areas slightly away from the subfloor layer.

So the carpenter was here and DH was available to discuss this with the carpenter while I was at work. DH read the underlayment article first. He had been an aerospace engineer years ago as a young adult before farming. He understands dynamics and the planning needed for these things. He spoke to the carpenter and he is very flexible and wants me to be satisfied with the out come. The carpenter is a gentleman.

Should I consider these fixes?
1)Take off the short sections where the butt joints meet at the joist and trim back 4" on the ones that will stay in place. Then add a new end section that is longer and butts up at new location, beyond the joist, with 1/8" gap. DH thinks we should just leave it.

2) carefully cut out the 1/4 gap at the periphery on the 3 walls were is is an issue. DH sees this as easy to do for the carpenter.

3) There is a small run of plywood the length of the room (110") and about 10" wide. Should this just get screwed done, omitting the glue? Or should it get prepped just like the rest of the floor to provide consistency for the floor?

I have to say, this early morning and late last night I was worried. This morning, when reviewing the situation with DH, and I was leaving for work, he said "I don't look at this as a crisis. I see it as a problem to solve". Isn't that the most wise thing! All I could see was the effort that went into the floor and the need for pulling it up and the $.

I'll be away for a week starting tomorrow AM. I'll be on retreat :) So if any post get made, I wont be back in internet range until next Thursday evening.

This project is on hold until than.

This post is in regards to the issue of no expansion gaps with the installation of the 3/4" plywood as mentioned in this thread.

The floor is still where I left off a week ago. It is 3/4" plywood, butted up tight against the stud walls, and about a 1/16" of space between the panels within the field. There are tighter gaps and looser gaps.

How can I create a gap at the stud wall? Can I leave it, and saw, or rout, out a channel several inches away from the wall? This margin would be so I can get the tool in place. This would leave just a narrow strip against the stud wall and an expansion gap on the other side of the 2-3" strip.

I am planning on taking my circular saw to the butt ends and the side edges, within the field area. But the tight fit against the stud wall is puzzling me.
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Sorry that I missed your previous. I was out of town too, your post fell off the main page by the time I got back.

Had your man glued down 1/4" or 3/8" ply my answer might be different. But the 3/4" sturdi-floor itself is pretty darn rigid.

Honestly, I wouldn't worry about it. Between your hubby being an aerospace engineer and having a farmer's common sense logic, and with me being an ex-rocket scientist, and you with your meticulous attention to detail, I think we have the ability to skin every cat from every technical perspective and then some.

If you truly want some sort of relief gap close to the stud wall "just in case", then sure, run a circular saw with the blade set at about 5/8" cutting depth around the perimeter of the room. The cut can be made several inches from the wall itself. You don't need to cut through the entire thickness of 3/4" ply. Then caulk the kerf to prevent SLC from filling it.

The kerf will absorb and movement that the expansion gap should have. But again, the 3/4" sturdi-ply isn't going to move much at all.

Plus you have Ditra.

Hey Mongo, thanks so much for responding. Now, I have cut the kerf but could not get into the corners. Should I leave that area or get my Fein Tool and finish the kerf, taking to the very corner to the intersection of the perpendicular kerf.

Another question. You mention early in this thread that with the 3/4" ply over my 1x plank, that this is good enough. So I have the 1x plank as my subfloor, and the 3/4" as my underlayment. If this is the case, do I still need the 3/8" plywood as underlayment that I was planning to use? I am hearing several opinions on whether I need another layer of ply, both in this thread and the JB forum. I would prefer not to elevate the bathroom floor with the addition of the 3/8" ply, but I will if I need to for structural integrity. So, can I safely leave out the 3/8" underlayment?

I told DH that I was going to ask you what the difference between a rocket scientist and and aerospace engineer. His response was (with a chuckle) "he'll just tell you to ask me". But he didn't give me an answer. What is the difference? I always thought they were one in the same. Anyway, I enjoyed your summary of our potential talents :)

Got home late this afternoon, so I've been off the forums for a few days.

Kerf cuts. I highly doubt if leaving the corners uncut would result in a stress raiser in the corner of the floor, but if you're motivated you certainly could continue the cuts to keep things consistent.

Since you're using Ditra, yes, you may omit the 3/8" ply.

AE versus RS, yep, they are indeed the same thing. Unless they are different. lol

Thanks Mongo for the info, I will leave the 3/8" out, and just go with the Ditra, unless I can get some of the Strata-mat. So far none locally.

I let the carpenter go today when he, once again, suggested that he skip today and come instead tomorrow to work. This is the final straw. Actually last Monday would have been, but he showed up and worked for 2 half days (Mon & Tues). I let him go on good terms. We reviewed where he was at in the project.

He has several strikes against him. He is irregular in showing up and doesn't put the hours in that are needed to complete this job. And he didn't seem to be able to plan ahead to anticipate the needs and the steps required to complete an aspect of the remodel.

So now I am trying to track down another carpenter to finish my walls and pocket doors. I have an old family friend that might come over, but he his reluctant due to his time constraints. So wish me luck.