Mortar bed under fiberglass whirlpool tub - How thick??

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Mookie3333

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I've run into something that I can't seem to figure out a solution to. I bought an American Standard Everclean whirlpool tub for a bathroom renovation in my home. This is going into a 5'x32" alcove.

When I take the tub out of the box, it sits VERY lop sided. OK - I figure I'd place it in the alcove, find a way to level it, mark for stringers, hang on stringers, and set it in a mud bed. After trying to lift/adjust the tub by raising or lowering the flange, I didn't accomplish anything.

I then removed the tub from the alcove, and tried to level it on the plain open floor. When I got it level, the apron was flush with the floor. BUT the drain side of the tub had basically a 2x4 (1.5" near the drain opening), and the back of the tub had a 2x3 (2.5") AND the fatter part of a shim (~1/4") for a total of ~2.75".

Does my mud bed need to be this thick??? I installed 2 tubs before and NEVER had to prepare a mud bed thicker than about 1 inch to get contact between the tub bottom and subfloor. What's going on here?? I picked up a bag of unmodified thinset thinking it would be enough. At this kind of thickness, I'd need 3 or 4 bags?? Is this a manufacturing defect, or is something totally wrong?

For the record, my subfloor is pretty level, +/- 1/4" along the 5' length of the tub, and level along the 32" width. I appreciate any help you guys can give me!
 

Terry

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I found this on some instructions for installing American Standard Whirlpools.

"This bath must be supported along its entire bottom. Use mortar as bedding material (do not use sand or foam). Apply enough mortar to support the complete bottom of the bath. After the mortar has been poured, and before it sets, position whirlpool or bath within recess until the rim is leveled against the leveling stringers (see "Typical Recess Installation") shown below"

I never support the "complete" bottom of the tub. That's impossible.
What I do, is place piles of mortar mix that have room to squish out as I drop the tub down.
Nobody is smart enough to know how much volumne is under the tub with all those strange measurements. You need some room for error.
I place the ledgers where I want them for a level install, place a few piles down, and then drop the tub down and allow it to squish them down.
Done!
It's the only way!
You can also lay some plastic between the tub and mortar and that works too. That way if you want to lift the tub out later, you can.

over-the-rim-drain-4.jpg
 
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Jadnashua

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Some companies actually have representatives that work in the field and help train installers and touch the products in the real world, some don't - the exchange of experience typically generates both a better product and better instructions. Some have a big budget in training, some have none. There can be a big difference in the accuracy of their instructions and even the ease of use of their products as a result.

Similar to how you notch thinset to set a tile expecting full coverage when done right, Terry's method can achieve essentially the same thing - support across the majority of the bottom of the tub.
 

Vegas_sparky

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Probably the same tub I put in my daughters bathroom. Use the online/paper cut sheet for ledger elevations. Get those ledgers level in both planes. Take your time here, and get it right.

Once the tub was in the alcove, I temporarily raised the drain end, and then attached the drain tailpiece through an access hole in that wall. I scooted some 4"+ high cow sized piles on the floor under the tub, lowered it on the piles, aligned the drain tailpice to P trap, slammed some more mortar in from the sides, then gently pressed the tub down in the mortar until it was on the ledgers. I never stepped in the tub, but did use foot pressure to get it close. You don't want to put much pressure on the tub bottom once you've hit the ledgers. The bottom may flex down, press out excessive mortar, and you leave a void when the weight is removed/bottom flexes back up. Check for level all the way around the tub. I added a few roofing nails around the flange, and left it overnight to set up. Once the mortar is mixed this all has to happen fairly quickly. I mixed my mortar a little loose to help it squish.

This thread has pictures.
 

Mookie3333

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Thanks alot guys for all your replies. I set the tub this weekend. It wasn't easy, and I always get nervous moving around a fiberglass tub too much. Someone should make a product that comes in a half gallon pail, pre mixed thick like peanut butter and ready to be squished down. I'd be more than willing to pay a few bucks for something like that. I mixed up thinset that I thought would be thick enough, but gravity just leveled it to lower than my ~3" needed if you didn't move fast enough. Placed the tub twice with inadequate coverage before getting it right the third time. I ended up building up the subfloor with some scrap wood and then dumped the thinset on top of that. I just made sure the tub was touching the ledger all around thumped the bottom of the tub which felt more solid than hollow as before when there was little coverage.

Great forum and great advice, as always. Thanks guys.
 

Mookie3333

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in tailpiece through an access hole in that wall. I scooted some 4"+ high cow sized piles on the floor under the tub, lowered it on the piles, aligned the drain tailpice to P trap, slammed some more mortar in from the sides, then gently pressed the tub down in the mortar until it was on the ledgers. I never stepped in the tub, but did use foot pressure to get it close. You don't want to put much pressure on the tub bottom once you've hit the ledgers. The bottom may flex down, press out excessive mortar, and you leave a void when the weight is removed/bottom flexes back up. Check for level all the way around the tub. I added a few roofing nails around the flange, and left it overnight to set up. Once the mortar is mixed this all has to happen fairly quickly. I mixed my mortar a little loose to help it squish.

holy $#%#.... I am so jealous at how neat your work is. That bathroom reno looks great. Your tile job is amazing too. Too bad you don't live near NYC, I'd offer you whatever you're asking to tile my bathroom! One question for you, seeing as you're an electrician - I'm looking to run a subpanel adjacent to my kitchen. Cabinets are very tight, and I really have no wall space to spare, other than a 12" width just beyond one run of cabinets. Is there a narrow panel that I can use in a space like this?? I know this is a totally different topic, but I definitely appreciate any help you can offer!
 

Jadnashua

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FWIW, thinset is not generally a good choice for something like this. It is designed for THIN installations, and tends to shrink and crack when applied over about 1/4" thick! Hope all works out well in the end. Especially if you used a modified thinset, I'd wait at least a few days before I did much of anything around it...the modifiers need to dry out. The cement in it will cure, but until the modifiers dry, things can still move around.
 

Mookie3333

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FWIW, thinset is not generally a good choice for something like this. It is designed for THIN installations, and tends to shrink and crack when applied over about 1/4" thick! Hope all works out well in the end. Especially if you used a modified thinset, I'd wait at least a few days before I did much of anything around it...the modifiers need to dry out. The cement in it will cure, but until the modifiers dry, things can still move around.

I used an unmodified thinset, and I built up about 2" with wood, and the thinset on top of that. Theoretically I would think I have <1" of thinset between the wood and tub. Still, more than 1/4" like you said. I can access the cutout where the drain is from underneath and shove something else in there, if there are voids remaining... I can also drill the subfloor from underneath and shoot something in other areas too. However, the only thing that seems like it would work (spray foam), the manual specifically says not to use foam.
 

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gott_tub_01.jpg


The ledger board on the back wall.

gott_tub_03.jpg


Reframed the wall on the valve side.

gott_tub_05.jpg


Someone else did the tile. I came back afterwards to set the trim.

gott_tub_07.jpg


A little bit of mortar and it was rock solid.
 

Jadnashua

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The hassle with spray foam is that it can exert huge forces on the tub as it expands, and literally warp, lift, or even break the tub. PLus, depending on the type you use, some can fracture when you apply a load to it, leaving a void, so you end up with no support. I've seen what happens to thinset when applied that thick...it tends to look like a dried lake bed. Some can work with thicker applications, and if so, they will say that on the spec sheet...but, most cannot.
 

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OK- I guess you live and learn. I wish I knew this last week! For what it's worth, I picked up a bag of sand cement. I'm going to mix it up dryish and take my time and pack it under the tub wherever I can get access. I made about 4 "piles" with wood and the thinset, so there are still some hollow areas that can be filled with sand cement. I can get access to those areas from underneath at the subfloor cutout for the drain, ~5/8" opening under the apron, and from either 32" side of the tub, it's just a 2x3 stud wall. Hopefully I can fix what I've done.
 

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Deck mud is a mixture of 3-5parts sand to one part (by volume) of Portland cement, mixed with just enough water to be like wet beach sand...it should hold together when you grab a handful and squeeze - the more cement, the stickier it gets. It's great in compressive strength, but isn't great for a wear surface because it has so much sand in it (it's meant to be covered with a wear surface but that isn't an issue underneath a tub!). It doesn't shrink if mixed properly or flow like concrete, but is packable. I'd take a spray bottle full of water and spray the area so the wood doesn't try to suck too much water out of the mix (normally, you'd use some plastic sheet to do this if you covered the floor first), then pack some in there.
 

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hi,

I'm about to install this same tub, never done a mortar bed before whats the best mortar to use?
I purchased full contact mortar , from underneath I measure about a one and three eighth gap...
did anyone else use wood also or just the mortar? my install I was about an inch to narrow on my length of rough opening so I notched out the studs so I can just slide tub in ..but now I'm wondering if that is ok with the mortar as its sliding in from the side rather then top down

any opinions and help would be appreciated ...

thanks
Mike
 

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I'm about to install this same tub, never done a mortar bed before whats the best mortar to use?
I purchased full contact mortar , from underneath I measure about a one and three eighth gap...
See https://terrylove.com/forums/index.php?threads/what-type-of-mortar-for-acrylic-tub-mortar-bed.55357/ That is not a special mortar. The mortar you purchased is probably fine if you get the right stiffness in your mix.

You don't want full contact. You want piles, so that the thickness can be determined by the piles smushing down under the weight of the bathtub filled with water. I suggest you use mortar piles as a search term in the search box above.
 

Admsav

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I've run into something that I can't seem to figure out a solution to. I bought an American Standard Everclean whirlpool tub for a bathroom renovation in my home. This is going into a 5'x32" alcove.

When I take the tub out of the box, it sits VERY lop sided. OK - I figure I'd place it in the alcove, find a way to level it, mark for stringers, hang on stringers, and set it in a mud bed. After trying to lift/adjust the tub by raising or lowering the flange, I didn't accomplish anything.

I then removed the tub from the alcove, and tried to level it on the plain open floor. When I got it level, the apron was flush with the floor. BUT the drain side of the tub had basically a 2x4 (1.5" near the drain opening), and the back of the tub had a 2x3 (2.5") AND the fatter part of a shim (~1/4") for a total of ~2.75".

Does my mud bed need to be this thick??? I installed 2 tubs before and NEVER had to prepare a mud bed thicker than about 1 inch to get contact between the tub bottom and subfloor. What's going on here?? I picked up a bag of unmodified thinset thinking it would be enough. At this kind of thickness, I'd need 3 or 4 bags?? Is this a manufacturing defect, or is something totally wrong?

For the record, my subfloor is pretty level, +/- 1/4" along the 5' length of the tub, and level along the 32" width. I appreciate any help you guys can give me!
How did you stop the mud from going into the opening around the drain? Is the tubs apron strong enough to support the side of the tub in a recessed installation?
 

Terry

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How did you stop the mud from going into the opening around the drain? Is the tubs apron strong enough to support the side of the tub in a recessed installation?

We're talking a few piles of mud. They don't go anywhere.
If you are installing a tub to level, the apron may not even be touching the floor in places. I would not count on the apron for support.

I never support the "complete" bottom of the tub. That's impossible.
What I do, is place piles of mortar mix that have room to squish out as I drop the tub down.
Nobody is smart enough to know how much volumne is under the tub with all those strange measurements. You need some room for error.
I place the ledgers where I want them for a level install, place a few piles down, and then drop the tub down and allow it to squish them down.
Done!
It's the only way!
You can also lay some plastic between the tub and mortar and that works too. That way if you want to lift the tub out later, you can.

 
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Trek4ward

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I've got a related question about the mortar bed. I'm doing a drop-in tub and am about the build the surround for it and was wondering if I need to add any height to it for the mortar bed? In other words, will I be squishing the tub down until it the surface touches the subfloor or will I leave some mortar beneath it which would raise the rim height slightly?
 
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