# installing new bathtub, secure using construction adhesive or mortar?



## Ron The Plumber (Jun 7, 2006)

We always use motor mix, it just feels right.


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## Sammy (Mar 11, 2007)

I have never replaced one but I am looking at doing one in the near future so I have been kinda keeping an eye out. 

I agree with Ron that the mortar base seems to make more sense in supporting the bottom of the unit versus just gluing a small area with construction adhesive to the floor. 

Some people foam underneath afterwards but the added support across the entire unit seems to be the best way to go for the long term. 

Let everybody know what you decide and how it works out!


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## bsd (Apr 21, 2007)

It's not just a small area. There are 6 manufactured supports to be glued, each is 4"x4", two rear, two center, two front. If I mortar, I have much more work to do as those areas CANNOT get any mortar on them and I have to place plastic liner all over the place. The adhesive route seems MUCH simpler.

I'm looking for a more definative answer than
"that's the way we always done it" 

I called Kohler, they said both are equal and that's why the two options are given.

Has anyone ever used the construction cement route? if so, any problems? vibration?

Thanks again,
Brian


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## Ron The Plumber (Jun 7, 2006)

Never used adhesive, but hay if you feel it will be good enough for you, then go for it, can't go wrong if manufacture say it works.


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## MikeF (Sep 28, 2006)

That's a proflex tub, we've installed just about all of them in that line. 

I'd skip the construction adhesive route, that's the "good" method instead of the "better" method. I'm sure you can handle the pro method. Just get a bag of non-shrink grout from Home Depot. Take your tub and put something like your construction adhesive on those 6 spots on the bottom of the tub then stick the tub in place, now pull it out, you should see the 6 spots on the sub-floor clearly where the mortar can't go, mix up some of the mortar, maybe 1/2 of a 5 gallon bucket or so and glob in on the sub-floor avoiding those 6 spots and stick that tub in place, all done. Get in it and mash it down. 

The construction adhesive is good, the mortar is better. Why, because the mortar will fill all the gaps under the tub and reduce the chance or even better eliminate the chances of any squeeking.

Don't forget to stuff some insulation anywhere you can around that tub to make it hold the heat better.


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## AtlanticWBConst. (May 12, 2006)

"Mike Finley" has entered the building....:detective: ....er, the DIY forum.......Welcome Mike.....


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## trimarts (Nov 16, 2008)

My tub has supporting blocks and i will go for the adhesive method.
reasons:
1.the mortar is very heavy and i need 2'' thick because of the blocks; i don't want to add more weight to the structure since the tub is a big one.
2. the mortar under the tub will cool the water very fast; with the mortar i will probably have 30 minutes until the water get cold.
http://www.trimarts.com


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## MikeF (Sep 28, 2006)

You need 1 bag of mortar. It weighs 50 lbs.

I'm not even going to go there in regard to mortar cooling the tub. That's wrong in about 50 different ways.

Bottom line is none of these tubs are constructed in a structural way, the exception is a cast iron tub and we aren't talking about those. Arcylic or fiberglass constructed tubs are not structural, they all flex they are all minimally engineered. To manufacturers shaving one extra ounce less of material equals $100,000 is savings over the life of that mold.

Mortar creates a solid base and eliminates flex. If you had two tubs one with mortar installation and one without and used them both you could easily tell us which one was installed which way just from use.

Mortar is the way professionals install tubs. DIYers will use anything but and come up with as many methods of mental masturbation as necessary to rationalize their choice.


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## buletbob (May 9, 2008)

I agree with MIKE the mortar is the way to go . Here in my part we use structolite it is like a gypsum mortar but does not have the weight of the mortar. its pretty light. most plumbing companies suggest using it. BOB


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## majakdragon (Sep 16, 2006)

Do you have a container of Plumbers Putty? Roll up a ball that "just" contacts the bottom of the tub between the center supports (or use two balls and place front and rear between the supports). Step into the tub or have the heaviest person in your house do it. Lift the tub and remove the putty and see if it is flattened at all. If so, you know the tub is flexing and needs more support. I see too many posts asking how to repair cracks in acrylic tubs. Anther problem with flexing is it tends to separate the caulk job around the top edge of the tub, at the wall. I use premixed mortar in a 5 gallon bucket. Be sure to use plastic under the mortar to prevent the wood fom sucking the moisture in the mortar out. Heat loss is not a problem with mortar. Use the mortar inbetween the support legs, especially in the center of the tub.


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## MikeVila (Nov 2, 2008)

I was under the impression that the mortar mix went under the legs and all. I read somewhere that when building the frame/island to add about an inch to your measurement because you would set the whirlpool in the mortar and then press it down and you would be about an inch higher than the actual height measured before setting it in the bed. Sounds like you guys are just spreading it out inbetween the legs and the belly?


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## MikeF (Sep 28, 2006)

Download the manufacturers installation instructions for the model tub you are installing, you should find that the tub is always designed to sit on the sub-floor.

When in doubt -- download the installation instructions.


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## majakdragon (Sep 16, 2006)

MikeVila. The mortarbed is to help support the bottom of the tub. Some of the legs and built-in supports do not do a good enough job.


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## MikeVila (Nov 2, 2008)

I'll have to go back and see how I can reconfigure my dimensions for my framing members for the island. I should be able to fix it without starting over lol. Alrighty then!!:thumbsup:


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## MikeF (Sep 28, 2006)

MikeVila said:


> I'll have to go back and see how I can reconfigure my dimensions for my framing members for the island. I should be able to fix it without starting over lol. Alrighty then!!:thumbsup:


You can always build up the sub-floor within your tub deck too. Just make it nice and sturdy and it's no different then the tub sitting on the sub-floor. Plywood and sleepers.


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## 360Flooring - Carver Tubs (Nov 14, 2008)

We have been manufacturing and installing our whirlpool & air massage bath tubs for over 20 years now and ALWAYS recommend using mortor.

Here is a link to our tub installation guide that will certainly be handy for your project: Carver Bath Tubs Installation Guide. Any other questions about the tub install..?


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## Floorwizard (Dec 5, 2003)

removed link.

Ads.


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## trimarts (Nov 16, 2008)

Mike Finley said:


> You need 1 bag of mortar. It weighs 50 lbs.
> 
> I'm not even going to go there in regard to mortar cooling the tub. That's wrong in about 50 different ways.
> 
> ...


My tub is a corner 5'x5' Kohler and is a very huge difference in strength compared with the old acrylic tub. I agree with you for a normal tub, one bag is enough, 1/2'' thick and the only solution is mortar; but for this tub i need 4 or 5 bags to fill the 2'' thick space under it. I think that is to much weight for a condo at the top floor.
The manufacturer indicate that the tub can be installed either with mortar or with adhesive.


Here is the thermal conductivity for some materials to give you an idea how fast your water get cold.
Cement, Portland 0.29 Concrete, stone 1.7 Air 0.025 Wood 0.04 - 0.4
The mortar under the tub cool down the water similar with a CPU cooler and if you have also air flow in the floor, you are set .

I know how it is to not have a cooler attached under the tub and for me is unacceptable that the water cool down so fast and if my tub allow me to do it without that cooler i will go for it.


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## DSKUP (Dec 24, 2008)

*Mortar bed under a Maax Advanta bathtub*

I'm preparing to install an Advanta "Picadilly" bathtub by Maax. I know from experience and reading this thread that a mortar bed is the conventional approach. However, this tub has a two pararallel 2x4s fixed to the underside of the tub, half buried in the fiberglass reinforcement and running its length. A mortar bed would have to be over 3" deep! Plus it would be a royal mess trying to get the tub out down the road. The instructions indicate that the tub should be set directly on the floor, and blocked to prevent movement. No mention of a mortar bed. The Maax website indicates that their tubs are designed "in such a way that they do not require a mortar bed." However mortar is recommended to level the floor. The bottom of the tub is very thick and stiff. Mortar just doesn't seem to make sense in this case. Any recommendations or experience with these tubs?

I'd like to avoid the hollow sound that I'd likely experience without a solid base.


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## wrangler (Oct 9, 2008)

If I understand correctly, the 2x4s leave you a hollow space down the middle of the tub that you'd prefer to be solid. How about filling that space with layers of foam board to bring the bottom of the tub flush with the reinforcing 2x4s, and _then_ use a thin mortar bed (enough to allow the surfaces of the 2x4s and foam to meet the subfloor)? It would eliminate the hollow sound/feel while adding a bit of insulating against the cold. Construction adhesive (preferably silicone based such as CWS) would work well for holding the foamboard to the tub bottom.


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## fixrite (Mar 1, 2009)

I was in the same dellema of what to use mortar or glue. Brother in law convinced me to go with mortar. It worked out fine, not cold as I insulated the sides of tub. A short time later had guests stay overnight. Hubby and wife had a nice jaccuzzi togeather, I was glad I had used mortar, togeather they were over 500 pounds of loving in my tub....uuuck the thought of it all..lol

Hope this helps
cheers


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## DSKUP (Dec 24, 2008)

For anyone out there with similar confusion regarding Maax Advanta tubs... Maax customer service replied to me that using a mortar bed is "strongly recommended. In fact, it's the best way to install."

Why the heck don't they just put this in their installation instructions? The install documents make no mention of mortar. The Maax website simply indicates that a mortar bed is "not required."

The only explanation I can come up with is liability involving DIYers. Strange indeed.


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## jogr (Jul 24, 2007)

I installed an acrylic tub years ago and didn't use the optional mortar bed. Boy did I regret that. The tub just didn't feel solid enough and would squeek. Next acrylic tub I install will be with a mortar bed.


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## DSKUP (Dec 24, 2008)

Thanks, I definitely plan to do so myself.


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