Shower Base flexes after mortar bed installation. Advice?

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Zerocool749

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Hi everyone,

Yesterday I installed an acrylic shower base, Dreamline Slimline, on my concrete basement slab. My floor was not level, so this is what I did:
1. I hot glued composite shims to the cement floor where the shower bases circular support rings would contact the cement. Hot glue was just to hold shim in place before mortar bed was added. I dry fitted the shower pan onto the shims to make sure it would be level on the shims. I marked my studs.

Here is what I mean by the circular support rings,
2022-05-29_12-53-08.png


2. Then, I laid piles of mortar at all of the circular supports with at least an 1" thick of mortar.
3. Then, I laid the shower pan, pushed it in place until it was level. I added bags of mortar for weight and let it cure for 24 hours.

Did I screw anything up in this process?

My Problem
After letting the mortar cure for 24 hours, I stepped on the pan. In the back corner, the pan flexes up and down. Everywhere else, it is solid, no flexing. Here's a picture of where I have this issue. It's in the corner area where it flexes up and down even with the pressure of my hand pushing it.

IMG_20220529_123639121.jpg


Here's a quick video -
What can I do? Here's a few ideas I had so far,

Idea 1 - Cut a notch in the 2x4 base plate and use a mortar bag to add more mortar in that area. I'm thinking I would do this without any weight on the pan, when it's flexed high. This way the mortar gets pushed against the shower base bottom, it cures, and then rests on that mortar. First, I wonder if I could even squeeze mortar out of a grout bag. I also wonder if I would get the mortar against the shower pan well enough.

2022-05-29_12-56-252.png


Idea 2 - Cut a notch in the 2x4 base plate use low expanding spray foam to fill in the cavity. I'm again thinking I would do this without any weight on the pan.

Idea 3 - Start over. I would have to rip out the entire shower pan, chisel off the existing mortar from the concrete, and lay another fresh layer of mortar. This would suck because it's a ton of work and I might ruin the $500 shower pan.

Help! Honestly, I do appreciate any help and advice.
 

Sylvan

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breplum

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Maybe:
1. Use non corrosive screw with wafer head into studs and then check to see if flex is gone.
2. If still an issue, instead of pouring standard mortar, (forget foam, which I foresee breaking down), use non expanding pour-able product like Rockite Cement.
Real challenge.
 

Zerocool749

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Hi Sylvan, I'm not sure how sheet lead or a new shower base would help this problem.

Hi Breplum, thanks for another option with the screws!

For the Rocktite Cement, did you mean expanding instead of non-expanding? The Rocktite cement does expand - https://www.acehardware.com/departm...e-cement-and-masonry/ready-mix-concrete/18448. Quikrete makes anchoring cement as well - https://www.homedepot.com/p/Quikrete-20-lb-Anchoring-Cement-124520/100318500.

I do see how it would expand against the shower pan, creating solid contact. I'd be worried that it would expand too much and push the shower pan off of the existing mortar bed, creating other problems. Hmm, thanks for another option to consider!

I figure if I try to add mortar to the area and it still doesn't work, I'm back to just starting over anyway. So it can't hurt to try.
 

Zerocool749

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Thanks for reading this Terry. Yes, I can push mortar mix under the pan. I had a couple questions on that:

Should I use more mortar or expanding cement?

Do I leave the pan flexed up while I push mix under pan? Or do I try to hold or weight the pan down while I push mortar under? I think I leave the pan flexed up since that's where it naturally want to pop to.
 

Terry

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Do I leave the pan flexed up while I push mix under pan? Or do I try to hold or weight the pan down while I push mortar under? I think I leave the pan flexed up since that's where it naturally want to pop to.
That's a tough one, the pan flexing up in the corner.
Two thoughts on that for sure. Do you ride with the the upward flex and push mortar in to support? Or do you pin the pan downward with some flat head lath screws? I don't know.

clare-2022-11.jpg


A pan I set last weekend in a 1907 home in Hoquiam, WA.
 

jadnashua

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Sounds like 1" was not enough! That area sounds like it was low, or you pressed it down further than needed, and the pan rebounded while the mortar underneath did not.

Did the pan actually bond to the mortar? It might just lift up.
 

Zerocool749

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Yes, exactly. Either it wasn't 1" or thick enough everywhere or it rebounded as I pressed down. The question is, what do I do now, lol.

I'm going to try to add more mortar first, then screw pan to studs. If neither works, I guess I rip it out and start over. That will suck.
 
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John Gayewski

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I generally level the pan and screw it into place for the curing process.

Don't use an expanding product, just the least viscous mortar or filler cement product you can find. Definitely a no on foam. You want to pour it and have it flow.
 

Zerocool749

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I generally level the pan and screw it into place for the curing process.

Don't use an expanding product, just the least viscous mortar or filler cement product you can find. Definitely a no on foam. You want to pour it and have it flow.

Thank you for the advice. I will make mortar with additional water so it flows easier, like cake batter instead of peanut butter. I will make sure not to exceed the maximum amount of water the package describes.

If you have any recommendations for a least viscous mortar or filler cement, I'd appreciate it!
 
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Jeff H Young

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Push the mortar in , and put screws through the flange. it will be rock solid Guaranteed Don't mix mud to wet it will slump
 

Reach4

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Thank you for the advice. I will make mortar with additional water so it flows easier, like cake batter instead of peanut butter. I will make sure not to exceed the maximum amount of water the package describes.

If you have any recommendations for a least viscous mortar or filler cement, I'd appreciate it!
Do you have access beneath? (basement or crawl space)
 

jadnashua

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Excess water in a mortar mix tends to cause it to shrink and crack when it cures...
 

Zerocool749

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Okay, thanks all!

Jeff, I'll follow your advice.

Reach, this is my basement so I can't reach underneath but I can reach from the side between studs. I can get tip of mortar bag pretty far in.

Jadnashua, thanks I won't make it too watery! I'll follow package.
 

Reach4

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You might make the mortar into balls and put those into sandwich bags. Then stuff the balls into place, with a ramrod stick, where the balls squish into shape to fit. Mortar does not require air to harden, and will be stronger if it cures slowly without drying.
 

Weekend Handyman

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You might make the mortar into balls and put those into sandwich bags. Then stuff the balls into place, with a ramrod stick, where the balls squish into shape to fit. Mortar does not require air to harden, and will be stronger if it cures slowly without drying.

Has anyone tried this? I would worry about the low friction between the plastic bags (more so on a bathtub).
 

jadnashua

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The pan doesn't need to be bonded to the mortar...the mortar is there for support so it doesn't flex. Some put plastic both underneath and over their mortar when bedding the tub or shower pan so it's easier to remove later, and it helps keep the moisture in place so you can get a full cure. As said, cement curing is a chemical reaction...drying doesn't make it stronger and can actually make it weaker. What water isn't used in the chemical reactions eventually evaporates or gets wicked away. The material:water ratio is there to ensure enough water for the reaction to occur (curing) and to make the material plastic enough to be formed as needed for the application.
 

Sylvan

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Hi Sylvan, I'm not sure how sheet lead or a new shower base would help this problem.

Hi Breplum, thanks for another option with the screws!

For the Rocktite Cement, did you mean expanding instead of non-expanding? The Rocktite cement does expand - https://www.acehardware.com/departm...e-cement-and-masonry/ready-mix-concrete/18448. Quikrete makes anchoring cement as well - https://www.homedepot.com/p/Quikrete-20-lb-Anchoring-Cement-124520/100318500.

I do see how it would expand against the shower pan, creating solid contact. I'd be worried that it would expand too much and push the shower pan off of the existing mortar bed, creating other problems. Hmm, thanks for another option to consider!

I figure if I try to add mortar to the area and it still doesn't work, I'm back to just starting over anyway. So it can't hurt to try.

This base does not rock but it is not cheap either



The Lead is placed on 3/4" CDX plywood which is leveled and then use flashing cement as added protection
 

Charlie Bosco

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Thank you for the advice. I will make mortar with additional water so it flows easier, like cake batter instead of peanut butter. I will make sure not to exceed the maximum amount of water the package describes.

If you have any recommendations for a least viscous mortar or filler cement, I'd appreciate it!
Put the mortar in a Cake Icing decorating bag with the nozzle on it. Then you can squeeze it just about where you want...
 
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