# Is mortar under bathtub necessary?



## CharlieR

Hey all,

Question. For a acrylic/fiber glass bath tub, not sure what exactly it is, how recommended is the mortar underneath for support? It has 4 feet, but I'm more concerned about the rest of the area where there isn't feet. It is a Kohler Archer tub if that is any help. I really want to do it, but a plumber has told me not to bother, should I see if he'll do it anyhow? 

THanks in advance for any advice.

Charlie


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## Alan

While the base may be strong enough to support the weight of the tub, we usually put mortar around where the legs sit, to prevent the tub from shifting horizontally after installation.

If it's your tub, and you want mortar under it, he should do it.


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## jaydevries

unless it is full contact bottom and sits level . i always set in piles or full bed set of mortar or speed set just due to the amount of units i have seen crack due to not enough support or over weight persons


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## joecaption

What's the directions say? Go online and check. If it says morter there's a reason for it.


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## funfool

When the plumber says do not bother with it, that skeers me and want to know more about the plumber. :huh:

For the couple of dollars and few minutes it takes, I would.
And once the tub is sitting in the wet mortar, I fill the tub with water for the weight.
This means dragging a hose through a window somewhere, or fetch it with 5 gallon buckets if needed.

But yeah, if I set that tub, is getting mortar and then filled with water while the mortar cures.


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## CraftsmanConnec

*Craftsman Connection - Do it right.*

I'm a kitchen and bath remodeling contractor for nearly 15 years. I've been a former building inspector and home inspector. Licensed General contractor in California and Texas, Angie's List Super Service Award winner in 2010, 2011, 2012.

The reason for the mortar bed is two fold:First the feet (aka shipping blocks) are not going to make the tub sit level, so the mortar also may be needed under the feet. Sometimes you won't see feet, there will just be a piece of OSB plywood.
Secondly, the vinyl/fiberglass will dry out and crack over time if it it stressed without support. I've seen hairline cracks in these types of tubs that are 10-20 years old. I don't think I remember seeing a mortar bed in all the tubs I've pulled out. Just because some builder or plumber is being or was lazy, doesn't mean that you should be. The mortar bed isn't easy for a beginner, but start by putting blocks under it to prop it up to get it level so you have an idea of how much mortar you will need. Don't make the mortar too wet or it will sag away from the tub as your setting it.


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## jaydevries

i do not recommend filling tub with water after setting in mortar bed due to the weight of the water will flex the tub pushing mortar down. which when water is drained will flex up causing a slight gap which causes a flex point in tub.
i am sorry to disagree with another post but this is what i have seen.
also if it is a full contact bottom ridgidized foam tub i use about 2 tubes of silicone underneath to prevent squeaking


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## funfool

Is why we have forums and discussions. 
How much do we think that new tub deflects when adding water? 
I think a brand new tub is not much, adding mortar under it and filling it with water, is only going to apply pressure in the same way applying pressure to wood glue allows it to have a stronger bond.

water is not required, I do not see a reason to quit adding it any time soon.


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## Alan

The other reason for not adding water when setting a tub : 


Typically we build our decks taller than the tub itself. This means using something to take up the space. It's never going to be just perfect.

Get it within an inch, and then float the tub in a bed of mortar.

Use shims or chunks of 1/8 plywood between the tub and the deck. This helps keep a uniform gap for caulking.


Now the reasoning : If you fill the tub with water, it will pull all the tub weight down from the rim of the tub. NOT the strongest part of the tub and it can crack.

If you let the mortar set up, then you can pull the shims, and the tub will always maintain the 1/8" gap and then you caulk the tub to the deck.

For alcove installations it's still a good idea, but usually alcove tubs have better support under them. If it was my own, i'd do it.


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## 747

yes for stability


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## CharlieR

Thanks everyone. I had planned to do most of this myself, but I am way behind schedule! Finding out DIY with little kids is not easy! 
Anyhow, appreciate all the feedback. I guess I can ask if he'll do it if I want and if not, get someone else, or someone to just do that part with me later or something. 
THe instructions mention an either or, mortar, or gluing the feet.... seems a bit difference to me, but what do I know! :wink:

It is an alcove installation. Does the rim still need support? I need to double check the instructions, but for some reason, I don't recall it mentioning that. I know the tub I took out had it. Seems like a good idea regardless.

Do any of you put any plastic sheeting between the mortar and the tub? I've read that is not a bad idea in case you need to remove it later, that it's not stuck to the mortar, just supported by it....


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## CharlieR

So follow up question. Can you put in Mortar support, after the tub is already installed? Kind of push it under for some added support? Once the tub is level already?


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## Alan

CharlieR said:


> So follow up question. Can you put in Mortar support, after the tub is already installed? Kind of push it under for some added support? Once the tub is level already?


Kinda depends on what the bottom of the tub looks like. Might be easy in some cases, but more difficult in others. I'm assuming you're asking because he refused to set it in mortar? :whistling2:


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## CharlieR

:whistling2:
Wouldn't say refused... lets just say strongly didn't think it was necessary and I'm unfortunately easily swayed / like to avoid confrontation and am behind schedule so the wife just wants things done :jester:

I can take a picture. Essentially there are 4 feet... integral skirt. However, I have access both from the foot of the tub, and slightly lesser access from the head of the tub... so I could scoop some in there and push it in... at least add some support in places other than the feet... provided the consistency of the mortar is such that this is a possible task?


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## retired guy 60

I agree with joecaption. Go online and see what the installation instructions call for with regard to your particular model tub. I came up with this from the Ask Me Help Desk:
"If the manufacture does not provide support ... then the installer must bed the tub himself. 
If the tub isn't bedded with mortar, cement or Structolite then it will 'flex and give' a bit every time someone steps into it. In time this can rupture the drain seal and develop a leak. It can also put a strain of the fittings below the drain. And now you know the rest of the story."


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## Ghostmaker

According to the manufacture install instructions the tub must rest on it's feet. They do not say to use any concrete additives. Make sure it is sitting on the floor and not supported by your deck. Also make sure you DO NOT install your faucet through the tub itself.
Kohler fiberglass has always been a top brand tub with thick over all construction. Follow the manufacture install anything else may void your warranty.


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## Alan

Ghostmaker said:


> sure you DO NOT install your faucet through the tub itself.


L O L ? :whistling2::whistling2:


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## Ghostmaker

Alan said:


> L O L ? :whistling2::whistling2:



Really, I read the instructions and they specifically say not to drill through the upper lip of the deck tub. And install the faucet through the deck itself. So may I ask what is so funny?


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## Alan

To the OP : It looks like they give you two options for setting the tub. 



kohler said:


> For mortar bed installation, set
> the basin area in 1" (25 mm) to 2"
> (51 mm) of mortar cement.
> 
> For adhesive installation, apply a
> generous amount of construction
> adhesive to the bath feet.


He should have done one or the other. I would have strongly requested that he did. Since they are giving you the option for adhesive, it looks as if they don't think their tub needs the extra support, and the mortar is just to lock the feet in place.
Your two options at this point are to pull the tub and put down some adhesive where the feet are, or try to shove enough mortar under the tub to lock the legs in place. If there's no tile on the walls yet, i'd vote for option A. It really would be a lot simpler. Mark one of the feet, pull the tub... measure for the rest of the feet...squirt some construction adhesive where your marks are, and put the tub back. Furthermore, since you made the request, he talked you out of it, and now the tub is moving around, he should come back and do it, IMO.


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## CharlieR

So yes, the tub is shimmed/resting on its feet. However, from my own opinion, the feet... seem somewhat inadequate compared to had mortar been used, but... it's done. It is sitting on shims, and the shims are screwed in place (from when the tub was put in place), and essentially the shim/feet are surrounded with PL glue. so although it's not "glued down", it is glue surrounded and I figured just as good? 

I mean, it feels generally fine standing in it, but ... Im an over-worrier 

What do you guys use to protect the tub while working in and around it? 

Somebody on another thread of mine suggested it's ok to stick the front legs of a ladder in the tub to reach up for higher work... should I stick something under it? Is that safe considering the tub is on it's feet and not mortared down? 

Thanks for all the help everyone.


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## retired guy 60

I would not put the legs of a ladder into a fiberglass tub for fear of damaging it. I would put a cloth painters tarp over the tub and then use the cardboard the tub came in to cut a portion to line the bottom. If you want to be ultra careful, remove your shoes before enterring the tub. This will probably seem excessive to everyone else, however. One of my concerns is damage caused by tools or tiles that are accidentally dropped into the tub during plumbling or tile installation and that applies to cast iron and steel tubs as well.


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## djlandkpl

Clean the tub first. Cover the tub with heavy duty plastic or a tarp. I used trash bags that I cut open so they would lay flat. Tape the plastic to the tub edge leaving room for your backerboard and tile. Tape the edge and seams so nothing can get behind it. Cut cardboard to line the bottom, sides, front, back and edge (that you step over to get in the tub). 

This will protect the tub from drops and any thinset that falls. I used a small ladder type step stool to do my tile. It fit perfectly in the tub and did not damage the tub at all.


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## CharlieR

Thanks guys! Ya, If I can find something that fits in the tub, that would be great, even better if it's plastic or something. I'll have to tape it up all nice and good. I like the cardboard idea. I was thinking foam, but cardboard is probably better for the thinset spills....


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## TheEplumber

You can buy plastic preformed tub liners....


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## COLDIRON

I never realized that many men were so interested in TUBS.

I thought most took showers. Seems like a lot of closet soaker's on here. Just kidding to break it up. What do you think klawman, Jarhead.?


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## plumbthat

*SAnd*

Similar question was raised in relation to a squeaky tub - you could support it with sand rather than mortar.


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## Seattle2k

plumbthat said:


> similar question was raised in relation to a squeaky tub - you could support it with sand rather than mortar.


o'rly?


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## Alan

Seattle2k said:


> o'rly?


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## keith teal

joecaption said:


> What's the directions say? Go online and check. If it says morter there's a reason for it.


what if there is no instructions


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