Filling in sunken living room / re-tiling house

[befuddledmeddler]

Hi Everyone!

Im looking for advice on my current project. We have to replace our cast iron plumbing and decided to make some changes to the house at the same time. We plan to fill in the sunken living room in our single story home on a concrete pad. The area is 20'x12'x6 inches deep. My plan is to fill it in with concrete before tiling my entire house with 6"x36" tiles. We will not be living in the house during this time but due to tight finances we are trying to keep our project timeline as short as possible.

I've considered the alternative of building a wood subfloor but my concerns are:
- The floor is not perfectly level (particularly around the edges due to the terrazzo flooring).
- I am concerned there would be a more hollow sound to the floor in our main living area compared to the tiling over the terrazo.
- Increased risk of damage to the tile at the transition areas between concrete foundation and wood subfloor due to expansion/contraction

Going forward with concrete, I am looking for recommendations on when it would be safe to tile. I understand 28 days seems to be a safe bet but it could be longer due to the depth.

Questions:
- How long should I wait until I tile and what can I do to confirm (on my own) I am good to proceed.
- Is there anything I can do to accelerate the drying process?
- Are there any recommendations on a thinset to use over the new pad that would limit the concern for residual moisture causing issues.

I would really appreciate any feedback or ideas anyone has that has done this before!

Thank you
Keith

[cx]

1. You should wait the 28 days as the industry recommends, but it's enti othing you can realistically do to determine that the slab might be ready before that. You can trowel or cut some control joints in the new concrete and watch to see if they crack. If they do, you've probably then experienced all or most of the expected shrinkage and I would be comfortable tiling. See my warranty information below.

2. You absolutely do not want to accelerate the drying of the concrete. What you want is for it to cure and I would want it to damp cure for at least the first ten days and preferably until you decide to tile over it.

3. I know of none. I think you'll find all the manufacturers of tile setting products recommending the same 28 day cure for concrete substrates.

As a side note, there is absolutely no requirement that the floor be level to tile it, but it wants to be very, very flat for those long tiles. No deviation from intended plane of more than 1/8th" in ten feet, nor 1/16th" in two feet. That's an exceptionally flat floor and difficult to achieve when floating a concrete surface.

You're also going to wanna make provisions for soft joints in the tile surface at all the construction joints where the new concrete meets the old.

My opinion; worth price charged.

[befuddledmeddler]

CX

While learning more about this project, I came across this from 2020.

https://www.johnbridge.com/vbulletin...=129806&page=2

It seems a better option would be for me to raise my pad about 4 inches then bond deck mud to bridge the remaining 2 inches. In determining how long until you can tile, you stated this (link to thread above):

Originally Posted by CX

1. The tile industry guidelines (TCNA) call for the concrete to be "well cured" and dimensionally stable. Not sure exactly what they consider "well cured," but a lot of the shrinkage will depend upon the amount of water in the initial mix, whether or not your concrete was reinforced, whether it was wet-cured, etc, etc. Were it mine I'd consider it dimensionally stable after about 7 days.

Not sure where Laz is getting his data (perhaps he'll tell us), but concrete is usually considered fully cured after 28 days. It might actually continue to gain strength for a hundred years or so, but who's counting, eh?

2. The tile industry (ANSI A108) requires deck mud to cure for a minimum of 20 hours before bonding tile to it, but indicates that longer cure times of up to 10 days are desirable."

Am I wrong to understand I may be able to proceed with tiling before 28 days using this approach?

I also hoped to see if I can get ideas on how to incorporate soft joints when laying tile at a 45 degree angle to the joint between the foundation and the new pad. Or if this is even possible/recommended. I read about non-linear soft joints but it seems like the joint would have to be perpendicular to the joint (correct me if Im wrong).

The yellow area is the approximate sunken area. While the dimensions are not exact, there will be a portion of 1 edge that will be under an island which will help hide a joint if needed. The brown console is in front of where the island will be.

[befuddledmeddler]

Picture clarifying tile direction, area, and mating edges

[cx]

Keith, if you'll visit our FAQ or the Liberry, you'll find a brief tutorial showing how best to post and properly attribute quotes here on the forums. I think that would cut down a lot on my confusion in your post #3. Can't tell if you're asking or telling or other in some of those statements.

Originally Posted by Keith

I read about non-linear soft joints but it seems like the joint would have to be perpendicular to the joint (correct me if Im wrong).

That one I can tell is a question, but I'm afraid I don't understand what you're asking. I can say that for your 6x36-inch tiles, I don't honestly think there is any effective way to make a sawtooth movement accommodation joint.

Will those joints between your new concrete confined within your old concrete still act fully as construction joints? I dunno, but I'd be reluctant to just tile over them and hope for the best.

Pouring part of the depth with concrete and finishing with deck mud would be a much better plan, in my opinion, and would allow you to actually achieve the industry standard flatness you really want.

My opinion; worth price charged.

[befuddledmeddler]

Post updated for formatting. The quote was attributed to you in a previous post linked above.

I appreciate the feedback on tile orientation.

Getting into this I was really counting on the new pad being contained within 4 solid walls would remove any concern for joint expansion but I have the growing concern we have to revaluate.

[befuddledmeddler]

CX

In my previous post I hoped you could clarify your comments on a similar project. The link below is the original thread for context.

https://www.johnbridge.com/vbulletin...=129806&page=2

Originally Posted by CX

1. The tile industry guidelines (TCNA) call for the concrete to be "well cured" and dimensionally stable. Not sure exactly what they consider "well cured," but a lot of the shrinkage will depend upon the amount of water in the initial mix, whether or not your concrete was reinforced, whether it was wet-cured, etc, etc. Were it mine I'd consider it dimensionally stable after about 7 days.



2. The tile industry (ANSI A108) requires deck mud to cure for a minimum of 20 hours before bonding tile to it, but indicates that longer cure times of up to 10 days are desirable."

Am I wrong to understand I may be able to proceed with tiling before 28 days using this approach?

Hit me with our thoughts.

[cx]

I'll stick with my #1 above. Won't nobody in the tile industry be your good friend if you have a problem with your tile installation, but I'd likely do with the concrete topped with deck mud. My customary warranty applies, of course.

My opinion; worth price charged.