Cracked Concrete Mortar Shower Pan Pour

[Interior Designer]

Hello Friends with Good Advice,
I am in the middle of a tub to shower renovation.

1. Plumber dug (10" x 18" ) concrete hole to access drain.
(Plumber said NO COVER was needed over the hole. Said vinyl liner with concrete would be solid.)

2. I covered the open hole with a (24" x 48") piece of free-floating sheet metal.
(We d id not fill hole with cement, because hole is open to drop ceiling of condo below.)

3. Plumber installed foam pre-slope and vinyl liner.
4. Tile guy poured the shower pan and cured for 3 days. (Pan was thinner, because of pre-slope.)

5. When stepped on, concrete mortar pan flexes and cracks all over, especially around hole.

We plan to Red Guard waterproof it.
Concerned large (24 x 48) tile inside shower may crack, since subfloor is flexing.

Q: Do I need to rip out pan and install a non-flexible sub-floor?
Q: If so, will a subfloor of 1/2" OSB and 1/2" cement board be non-flexible? Should I glue it down with thin-set?

THANK YOU IN ADVANCE!

 

[Breplum]

Shooting from the hip here. I am a plumbing contractor, not an engineer. We always patch concrete for stability.
I would tear out what is there. Piece and screw sheet metal and rig it to be a bottom form for new high psi concrete pour after doweling in rebar pins to keep it stable once cured. A extra cautious step would have you epoxy the dowel pins in.
I've never been around modern high rise. Is that a "post tensioned" structural metal piece in the first picture?

 

[Sponsor]

 

[wwhitney]

1. Plumber dug (10" x 18" ) concrete hole to access drain.
(Plumber said NO COVER was needed over the hole. Said vinyl liner with concrete would be solid.)

Plumber is not an engineer, and obviously was wrong. Start over by consulting a qualified professional on how to properly repair the hole in the concrete slab. Could be an engineer, or could be a general/concrete contractor who's experienced with suspended slabs

Cheers, Wayne

 

[Jeff H Young]

Id tear it out and fix to my liking. similar to breplum advice. But you could consult engineer, have a site visit, pull permit , open wallet , and see how it goes . but personaly Id fix it

 

[Interior Designer]

Thank you for your responses.
Seems like common sense to me to build a rigid, secure subfloor for the shower pan. However, the job is permitted and has passed inspection! The plumber and the tile guy (both licensed and experienced) are saying the hole in the concrete floor and the flexibility of the sheet metal over the hole will not matter in the end, because the thinset and tile will hold firm, (even thought the cement mortar poured pan has flexed and cracked over the hole). Could that be true? I want to have peace of mind that there will be no problem in the future.

 

[wwhitney]

Well, the path to peace of mind for me would be repairing the slab underneath the pan. I don't think mortar or tile or sheet metal are sufficiently structural to span that hole.

But if you don't want to believe a few random people from the Internet, why not find someone local who's knowledgeable and whom you'd trust? Also, since you said the neighbor's condo is underneath, the condo association or building may have some rules about holes in the slab you need to follow.

Inspection is no guarantee of compliance, inspectors miss things all the time. The best we can reasonably hope for from an inspector is to catch all the big things and to avoid making up violations.

P.S. You might try asking at the johnbridge.com forum, they are gurus for all things tile related, and there are a couple contractors there you are frequent posters and could opine about the hole in the slab. Providing the hole dimensions would be helpful, too.

Cheers, Wayne

 

[Tuttles Revenge]

No chance I would leave a hole with a sheet metal patch over it.

Inspectors aren't there to guarantee your liability. That's 100% on you.

 

[Gsmith22]

Is the hole in the structural slab or some sort of topping slab over the structural slab? The first picture would seem to indicate the "reinforcing steel" you uncovered in the hole is a some sort of tensioning cable. No sleeve on the cable so you would think pre-tensioning cable but that would be odd in anything but precast concrete so I would have expected post-tensioning cable with sleeve for a structural slab in florida. Regardless, that type of cable is in a structural slab and not a topping slab. Under no circumstance should you cut that cable and of course, the integrity of the structural slab relies upon the bond between the concrete and cable. I think you need an engineer here before this blows up and destabilizes more than just your shower.

And obviously, the plumber and inspector couldn't be more wrong. Plumbers aren't structural engineers so ignore whatever he says and inspectors will disappear like a fart in the wind when liability raises its head. As tuttles revenge indicated, you hold the liability for making the hole.

if your floor isn't stiff, the tile is going to move and crack. Repair here requires making the floor what it was before the hole was dug. Sheet metal plate and thin topping patch will never work.

 

[Gsmith22]

actually, in looking at the photo and your description further, if you see the drop ceiling in the condo below, you definitely cut through the structural slab. I would have never recommended that to get to a drain that would have been accessible from below. I know, you would have had to deal with adjacent condo owner but that will pale in comparison to what you are going to have to deal with now. You now have liability for replacing the structural slab in a competent manner that doesn't result in floor collapse as you take a shower (ie think waterfall into their condo with your feat hanging through the ceiling ala Tom Hanks in Money Pit). Get a structural engineer to evaluate and recommend a repair. Min, going to have to drill and epoxy reinforcing bars into slab edges and recast slab to integrate new concrete at hole with existing slab. Probably have to put formwork in from below to contain new concrete.

 

[Tuttles Revenge]

Brought in a radar imaging company to certify where the cables were before estimating the project just to install a shower pan on existing. Previous installer of the second pan that failed started to chip away at the concrete and was only stopped because neighbors complained. Homeowner then thought to bring in a GC to oversee the project. With careful measurements and precise work we were able to make minimum modifications without harm to the structure.

 

[Interior Designer]

Dear Wayne,
Thank you for your reply. All of the responses confirmed our own thinking. Rip out and build a rigid and secure sub-floor for peace of mind. I will check out the other forum. Thank you for this information.

 

[Jadnashua]

I'd consider placing a 3/4" piece of plywood over the entire shower area and use some flat-head Tapcons to anchor it firmly to the slab. 5/8" could be enough, but for that extra 1/8", I'd go with the nominal 3/4". You want the ply to have all plies at least 'C' or better and to have exposure 1 or EXT glue. Normally, you'd not want to use ply directly on a slab, but on an elevated one, it shouldn't be an issue. If you were worried about that contact, you could put down a sheet of plastic first.

It's good that they are planning a preslope, but I cannot tell for sure what they actually used. The generally accepted material is a sand topping mix, or a mix of 5:1 sand:cement. Some go a little richer, but it becomes harder to pack as the cement makes it stickier. The stuff when mixed right, is more like wet beach sand than a concrete mix. The other area that often gets messed up is the curb...you cannot just screw some cement board to the curb...code calls for NO fasteners below 3" above the top of the curb, so how are screws into it supposed to pass? And, no, RedGard does not fix that.

My preference is to not use that conventional liner technique, but to use a surface applied membrane. Kerdi is one, and it requires a different kind of drain, but you only need to make one layer, then the waterproofing layer goes on, and the tile is attached to it. This makes the entire shower waterproof immediately beneath the tile.

 

[wwhitney]

If a qualified individual signs off on the idea that the hole itself is not a problem for the structural integrity of the slab, then 3/4" plywood would be a fine work around for the shower pan. However, the slab may require repair for structural reasons, in which case there will be no need for the 3/4" plywood. If I had to guess, I'd guess the latter.

Cheers, Wayne

 

[Interior Designer]

Thanks for all of everyone's thoughts.

The hole in the floor was put there when the building was built. (The original 5' tub drain came through this hole in the concrete floor. All apartments are built this way. The bathroom pipes run through the ceiling of the neighbor beneath.) However, the plumber did make the existing hole bigger, in order to access. He, also, made a new hole for the location of the new drain, (For this we got permission from the neighbor downstairs, went through his ceiling and patched.) The hole for the new drain location is not in question because it is basically, the size of the drain. It's the original tub hole that is big (maybe 10" x 18"?) and in the center of the shower.

Nice work avoiding the reinforcing steel tension rods, TUTTLES.

Exactly, WAYNE. If someone qualified signs off on the idea (the existing hole made larger, is still of structural integrity) we are good! Does the slab need to be repaired? Good question. Peace of mind.

Thanks, JUDNASHUA. You sound very professional. We were thinking: leave the hole in floor (would we need for future access?) Glue down sheet metal. Red Guard concrete floor. 1/2" OSB Plywood attached to concrete with Hilti gun, then 1/2" cement board screwed down (countersunk) to OSB. Vinyl liner over cement board. Remove pre-slope and allow the poured pan of Quicrete to be thicker and stronger. Been watching Starr Tile YouTube videos. Since cement wicks up water into dry areas, not sure pre-slope would assist in draining toward weep holes. Kerdi is nice, May not be necessary. What kind of glue do you use to adhere cement board inside vinyl liner curb? Thinset? Liquid nails?

GSMITH22: I agree. If the shower pan is not stiff, the tile may move and crack. I suppose, if the plumbing fails in any apartment here, it is a waterfall scenario. All of our concrete slab floors have holes where the pipes come up through the neighbor's ceiling.

BREPLUM and LOVE, thank you for your early response and structural engineering ideas. (I do not know if post-tensioned. I think they are prefabricated concrete slabs that fit together. Maybe 6" thick. Built 1970.) Ah! Basically pour a new floor in the entire pan area.

 

[Jadnashua]

For building your shower basic questions, check out www.johnbridge.com .

If you're going with a conventional shower build (like with the liner you showed), there is NO cement board used on the curb...you need to use some metal lath and mortar to build up the tiled surface on the curb. This is fat mud, not deck mud so it is stronger and can hold together on its own. Deck mud is not particularly strong, but it's great in compression and stable. On top of the liner, it works because it is porous. Neither the tile nor the grout is waterproof...it is a decorative wear surface. Water WILL get beneath the tile, and the setting material beneath MUST be porous and sloped so that moisture can percolate towards the drain and flow out the weep holes (which, must be kept clear during the build - often a failure point).

Cement board is not structural, and, in this case under your shower pan, serves no purpose. If you go with plywood, that will be fine. The layers from the floor up would be:
- plastic moisture barrier - probably not needed on an elevated slab, but won't hurt
- plywood anchored into the slab
- another layer of plastic sheet (so the ply doesn't suck moisture out of the deck mud when you apply it)
- metal lath stapled to the ply
- deck mud for preslope
- liner
- setting bed
- thinset
- tile

Should you go with a Kerdi shower, the layers would be the same as above up to the deck mud for the preslope:
- Kerdi
- thinset
- tile

So, this buildup would mean your shower floor would be nearly two inches lower since your setting bed typically would need to be at least 1-1/4" thick on top of the liner.

 

[Jeff H Young]

Thank you for your responses.
Seems like common sense to me to build a rigid, secure subfloor for the shower pan. However, the job is permitted and has passed inspection! The plumber and the tile guy (both licensed and experienced) are saying the hole in the concrete floor and the flexibility of the sheet metal over the hole will not matter in the end, because the thinset and tile will hold firm, (even thought the cement mortar poured pan has flexed and cracked over the hole). Could that be true? I want to have pea ce of mind that there will be no problem in the future.

once the floor is floated it would likely make floor more solid. depending on job I would advice repair around hole but likely wouldnt perform that work unless part of my job. in which case Id pin it with rebar doweled to sides . more than one way to do it and their way might hold up but not in my home. just an opinion but doubt that meets any recommended standard Im not a structural expert

 

[Jadnashua]

Deck mud needs a stable base as structurally, it is very weak. As I said, it's great in compression, but any movement will cause it to crack and maybe eventually pulverize...it is a very weak sand:cement mix. If the slab was intact, you could do a bonded mudbed, and that would be fine (and could be thinner). But, to span the holes, you need something strong, and a thin metal sheet isn't it! A steel plate could work, but that is lots more expensive than a sheet of plywood. It is very hard to make a preslope out of a concrete mix as it tends to slump too much. You cannot use concrete as your setting bed, as it needs to be quite porous to work well, which is why deck mud is called for. If you use a surface applied membrane, you don't need the setting bed as you put it on what would have been called the preslope, so it's simpler. I'm not an advocate of liquid applied waterproofing for a shower pan. Yes, it can work, but it's lots harder to install properly than a sheet membrane. One would think that it's just painted on, but it needs to be applied a certain thickness without pin holes or runs, and that's harder than people think. And, too thick (actually, hard to do) is not better.

 

[Gsmith22]

Thanks for all of everyone's thoughts.

The hole in the floor was put there when the building was built. (The original 5' tub drain came through this hole in the concrete floor. All apartments are built this way. The bathroom pipes run through the ceiling of the neighbor beneath.) However, the plumber did make the existing hole bigger, in order to access. He, also, made a new hole for the location of the new drain, (For this we got permission from the neighbor downstairs, went through his ceiling and patched.) The hole for the new drain location is not in question because it is basically, the size of the drain. It's the original tub hole that is big (maybe 10" x 18"?) and in the center of the shower.

Nice work avoiding the reinforcing steel tension rods, TUTTLES.

Exactly, WAYNE. If someone qualified signs off on the idea (the existing hole made larger, is still of structural integrity) we are good! Does the slab need to be repaired? Good question. Peace of mind.

Thanks, JUDNASHUA. You sound very professional. We were thinking: leave the hole in floor (would we need for future access?) Glue down sheet metal. Red Guard concrete floor. 1/2" OSB Plywood attached to concrete with Hilti gun, then 1/2" cement board screwed down (countersunk) to OSB. Vinyl liner over cement board. Remove pre-slope and allow the poured pan of Quicrete to be thicker and stronger. Been watching Starr Tile YouTube videos. Since cement wicks up water into dry areas, not sure pre-slope would assist in draining toward weep holes. Kerdi is nice, May not be necessary. What kind of glue do you use to adhere cement board inside vinyl liner curb? Thinset? Liquid nails?

GSMITH22: I agree. If the shower pan is not stiff, the tile may move and crack. I suppose, if the plumbing fails in any apartment here, it is a waterfall scenario. All of our concrete slab floors have holes where the pipes come up through the neighbor's ceiling.

BREPLUM and LOVE, thank you for your early response and structural engineering ideas. (I do not know if post-tensioned. I think they are prefabricated concrete slabs that fit together. Maybe 6" thick. Built 1970.) Ah! Basically pour a new floor in the entire pan area.

I should have prefaced my prior comments with the fact that I am a structural engineer. "I think they are prefabricated concrete slabs that fit together. Maybe 6" thick." This additional information is starting to make more sense now. So the steel strand that you see is definitely a pre-tensioned cable (since this is precast/no sleeve around cable which would be post-tensioned). The cable is tensioned in precast yard, concrete cast around it and when sufficiently hardened, they cut the cable ends causing cable to shorten (tension is released) which compress the concrete around the cable (as it shortens) due to bond between concrete and cable. So when you break out the concrete around a pre-tensioned cable, it loses some of the bond along the cable length and thus some of the pre-tensioning, and thus some of the slab's ability to withstand bending from vertical load. How much is hard to know because there aren't enough details but if you say they are all done this way since the 70s and no one reports any issues (excessive deflection, cracks, etc.) its probably nominally fine. But don't go making the hole bigger. That plumber doesn't have enough insurance to cover what could happen.

To your other issue, you need to have something that will span the hole in a structural manner. Tile, mud beds, concrete board, etc. are all not structural and will break, deflect, crack into that hole (as you have discovered). 3/4" plywood (not OSB that stuff is crap) would probably fit the bill but then you need all kinds of waterproofing above it so it never sees a drop of water. If the plywood gets wet, it isn't going to dry and then it will rot and you will be ripping this all out and starting over. The waterproofing part (once the structural part is solved) is paramount here.

 

[Reach4]

It seems to me that plumbing in this building needs to be done through the drop ceiling of the unit below.

There has been structural damage to the building IMO.

If I were to try to cover this up and support a shower, I would think at least 1/4 inch steel plate would be called for-- certainly nothing that would be described as sheet metal.

But it best for the building if the building management were to get this looked into.

 

[WorthFlorida]

If you do tear out the concrete, I would replace it with fiberglass reinforced mix.

https://www.homedepot.com/p/SAKRETE-80-lb-Crack-Resistant-Concrete-Mix-65201090/100390848