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bsd 04-21-2007 10:10 AM

installing new bathtub, secure using construction adhesive or mortar?
I just bought a new whirlpool bathtub replacement for my std 5' tub. It's a Kohler K-1357 and the installation instructions are here.

On page 6 of the installation instructions you have to choose either mortar OR construction adhesive for the installation.

I would prefer construction adhesive as it appears to be much simpler.

I was wondering if there was anyone on this forum who had used one or the other, or maybe a contractor whose done it both ways, to explain how or why one approach would be superior to the other.

If I elect to use the construction adhesive method, is there any recommended prep for the subfloor?

Any non-obvious repercussions of this decision?

Thanks in advance,

Ron The Plumber 04-23-2007 06:34 PM

We always use motor mix, it just feels right.

Sammy 04-23-2007 07:06 PM

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!

bsd 04-23-2007 07:24 PM

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,

Ron The Plumber 04-23-2007 07:29 PM

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.

Mike Finley 04-23-2007 07:32 PM

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.

AtlanticWBConst. 04-23-2007 07:49 PM

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

trimarts 11-15-2008 09:55 PM

My tub has supporting blocks and i will go for the adhesive method.
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.

Mike Finley 11-16-2008 10:16 AM

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.

buletbob 11-16-2008 10:32 AM

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

majakdragon 11-16-2008 01:12 PM

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.

MikeVila 11-16-2008 03:58 PM

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?

Mike Finley 11-16-2008 06:23 PM

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.

majakdragon 11-16-2008 09:28 PM

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.

MikeVila 11-17-2008 12:05 PM

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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