Flattening, Crack Isolation, Expansion Gap Questions [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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12-20-2016, 03:44 PM
I ran across this forum today, and wanted to run my project by you guys to see if you can help make sure I’m doing it right. I’ve a myriad of questions below!

I sadly already have tiled my laundry/bath, so that room is committed at this point.

My hall / media closet are out of flatness for the tile (3/6 to ¼ flatness variance for both small rooms). My Rec room has levelness and flatness issues. 1.5” out of level over 20 ft and after grinding I am ½” out of flat in 8 ft. There are some humps, ridges & valleys. There are three settlement cracks in the rec room that are 1/32 to 1/16 wide, no height variations. My thought was to spot-flatten the values my pouring levelquik RS and then screeding it with 6 or 8 ft levels. Since I have a grade in the room, will it stay? Or start running downhill. Do I need to screed it right away and then again in 3-4 mins once it is near the end of its ‘flow’ time are? Should I let it fill the settlement cracks, or caulk them?

Useful Details:
The slab is 38 years old.
Slab Patch was aged 8 weeks prior to tiling (cut was for plumbing).
Floors were ground with a 10” wheel – surfaces are clean & of even texture
Located in the Northwest

Tile: 12x24 porcelain
Spacing: 1/8” Grout Lines & 1/3 Brick Pattern, laddered. Near zero variance in tile dimensions, ~1/16" cupping
Grout: QuartzLock2 Urethane Grout
Mortar: Versabond LFT, Modified Mortar
SLU: LevelQuik RS (?)

1. For the large room, is one staggered expansion joint on the 20’ dimension acceptable?
a. Can it be a standard 1/8” Grout Line?
2. I had planned to do a brick ladder 1/3 offset in my Rec Room, but since I think I need an expansion joint in the room, does the 1/3 stagger work for this? (shown in sketch)
3. Should I be using crack isolation membrane?
a. I sure as heck don’t want my installation to fail, but covering the floor with membrane adds $300-500 to the project, and I’m a bit over-run as it is. If it’s a <1% risk to not use it, I don’t want to use it. If it’s a 20% risk, I definitely want to use it.
b. If I should be using it, should I cover the entire floor, or only the settlement cracks?
c. If using it, I was going to use NAC ECB Anti-Fracture membrane. Alternate suggestions, or it is a decent one?
4. Lastly, Since I have two doors that I want to ensure my tile runs parallel to on opposite sides of the room, how would I best lay out the tile on a large room like this. By quadrants? I don't think the walls are exactly parallel, off maybe 1/4 to 1/2" from square.

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12-21-2016, 10:24 AM
Adding Images.

12-21-2016, 05:39 PM
I'm not a big SLC fan but I know it does work. Instead, I'd bond a dry pack mud bed to the slab and then the membrane would then go over the mud bed.
It's not going by the book but I would apply the membrane wall to wall. Then, when tiling, I'd make sure I leave a gap at all the walls and then I would skip the expansion joint. Most folks don't want an expansion joint running thru the middle of their floor. I've tiled much larger rooms than that without a expansion joint without problems. If you use a paint on membrane, just make sure you apply it thick enough. A thickness gauge is best used for this. It's hard to say what your chances are. With that many cracks, there's no way I'd tile directly to the slab.

12-22-2016, 12:01 AM
Separate question - I found two tiles that didn't bond properly (hollow taps) this evening, so pulled them. Can anyone explain why they failed to bond? My nephew and I were working in tandem, and this was near the finish, so I wasn't watching as closely as early on. He was laying thinset while I was placing and leveling.

Also, this was my first time using leveling system.

The failed area didn't have the trowel notches showing.

1/2" trowel, versa bond LFT

Todd Groettum
12-22-2016, 07:59 AM
Did you burn some thinset into the slab with flat side of the trowel? Could be a residue on the slab of some type...
Example...very few things stick to thompsons water seal....

12-22-2016, 09:39 AM
Looks to me like the mortar stuck well enough to the substrate. I'd wanna know if the mortar was keyed-in to the backs of the tiles in that case.

12-22-2016, 10:01 AM
Notched on the slab side - back buttered onto the tiles with the flat side. of the trowel. We were in disagreement on the backbutter... i was aiming for a thin layer to just coat/wet the surface of the tile, he sometimes was laying it in.

I was torque'ing the leveling posts quite a bit. My naive(?) theory is that its possible this tile was under (or over) filled compared to his neighbors, so i pulled it off its bed with the posts.

I ground the slab, swept vacuumed and mopped (plain water). so the slab is about as clean as it could possibly be. There was previously mastic (from 80s linoleum & parquet) everywhere.

12-22-2016, 10:17 AM
theory is that its possible this tile was under filled compared to his neighbors, so i pulled it off its bed with the posts.

Looks like a very good theory of why the tile didn't bond properly .


Coverage -- not enough mortar under the tile -- is very important to avoid while using the leveling systems .

Did you end up using any uncoupling membranes ?

12-22-2016, 12:40 PM
to be clear - the green bpx in your post is where i had the hollow taps - which i thought was strange as can be. the striated region was solidly attached.

I did not in this room - i kind of wish I did as the patch shown in my first post's sketch is new relative to the old slab. I can just imagine a crack right across this room where the two are joined.

I'm still struggling if i should or should not use an uncoupling membrane on the large rec room. I was hoping for a few suggestions there. If I do use one, paint on is as good as the peel n stick ones? If so, any specific suggestions for paint on? Do local stores carry these? seems like everyone I have called only carries Ditra.

12-22-2016, 01:10 PM
The green area is to reflect how a proper coverage should like . But there is also wet mortar looking in your picture and the question would be , was the mortar cured or enough strength achieved to say improper bonding just from hollow sound when tapped ?

Another question would be if any rocking motion is present? , meaning the flat mortared area was pressed more onto mortar , prior to applying the leveling process , then it got lifted by it , due to improper amount of mortar applied .

Hard to say with a precise % , but it looks like a combination of improper amount of mortar in combination with a leveling system , if mortar was cured enough to rely on a tapping technique , to verify hollow spots on the installation .

12-22-2016, 01:15 PM
Perhaps I was tapping at it pre-maturely then..? It was 24h after setting. No rocking. Only these two sites were hollow when tapping. I think the batch of mortar that these two were set in was a bit on the wet side.

Thanks for clarifying on the coverage - we will work to get that improved in the next room.

03-06-2017, 12:50 PM
Back with a question! (and an update)

First the question: How long should I wait between setting the tile and walking on it, and then grouting? My inclination was to wait 5 days to grout, but was hoping to walk in 24h.
Porcelain tile & ECB75 Crack Isolation membrane
Mortar: Versabond LFT
Grout: Quartzlock2 Urethane Grout

I have to say the ECB was quite frustrating to install. :devil:The primer is the glue for that stuff, so its difficult to not walk on it, and caused all manner of problems getting started. I did find that the yellow side of the paper for the ECB rolls was the *only* thing that didnt stick to the primer. White side sticks, and of course laying out a roll, its the white side that touches the glue. Two more rows of ECB tonight and then we're off and running with tilework.

03-06-2017, 03:43 PM
1. Usually you're safe to walk within 24hr, if you are a larger individual maybe a bit longer. Usually if lippage control system in is place a little sooner is ok. It's all relative to the curing of the thinset, temp, humidity, tile, and substrate...usually 48hrs is safe to grout but the longer the better, defer to the thinset and grout instructions and follow what your product says.