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Thread: Type S Mortar bed for tub

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    DIY Junior Member patrick1's Avatar
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    Default Type S Mortar bed for tub

    hey guys,

    Last night I set my bathtub in a bed of mortar. It is perfectly level now but I am not sure how long the mortar needs to cure for before we can shower or take a bath. It is the Sakrete type s pre mix masonry mortar from Home Depot. I mixed it pretty thick it so I am assuming the cure time would be a little less than if I made it watery.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Well, that isn't what I'd use, but after a day, it should be cured enough. All cement products reach their stated strength in 28-days, but reach probably 70% in the first day or so. The load on it isn't very much per square in, so it should be fine. Adding more water than stated, doesn't change the cure rate, but does affect the strength. Not enough, and it can't create all the bonds it should.

    The mixture doesn't 'dry', it gets chemically combined with the cement. Excess messes up the matrix, too little, and you get incomplete bonds. It has enough affinity for moisture that it will pull it out of the air to complete the matrix, but that takes time and can subject it to damage in the interim. A better substance is a sand mix (deck mud) or structolite for this application. Not sure what the lime (which makes it type S) will do in the long term...maybe nothing.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member dlarrivee's Avatar
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    Did you put a sheet of poly over the mortar to keep it from contacting the tub itself?

    I assume it's a acrylic/fibreglass tub?

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    Test, Don't Guess! cacher_chick's Avatar
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    I'm not sure where these fellas are steering you...... I know for a fact that Kohler recommends installing their acrylic shower pans in a bed of masonry mortar with no plastic or anything else. I wouldn't let them worry you.

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    DIY Senior Member dlarrivee's Avatar
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    Quote Originally Posted by cacher_chick View Post
    I'm not sure where these fellas are steering you...... I know for a fact that Kohler recommends installing their acrylic shower pans in a bed of masonry mortar with no plastic or anything else. I wouldn't let them worry you.
    I guarantee they don't recommend a mortar with hydrated lime in it.

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    Test, Don't Guess! cacher_chick's Avatar
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    What comes with your guarantee?

    The technical support folks at Kohler specify portland cement mortar, which to my knowledge always has lime in it, no matter if it it is S, M, N, etc.

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    DIY Junior Member patrick1's Avatar
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    the tub has a hard foam bottom. Its some type of Polycomposite tub.

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    DIY Senior Member dlarrivee's Avatar
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    Quote Originally Posted by cacher_chick View Post
    What comes with your guarantee?

    The technical support folks at Kohler specify portland cement mortar, which to my knowledge always has lime in it, no matter if it it is S, M, N, etc.
    Portland cement doesn't mean lime...

    Mortar can be sand and cement...

    Can you show us where every manufacturer follows Kohlers suggestion of "masonry" mortar, or even just Kohler's?

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    DIY Junior Member patrick1's Avatar
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    I didn't mean to start an argument, but I guess that happens in all forums lol... I just hope my tub is okay.

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    DIY Senior Member dlarrivee's Avatar
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    I think it will be fine, you did a better job than most would just by using mortar under it.

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    DIY Junior Member patrick1's Avatar
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    This is semi off topic but why does the manufacture say not to use a ledger? I didnt use one since the manual said not to but I dont understand why that would harm anything.

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    DIY Senior Member dlarrivee's Avatar
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    Most of the newer tubs have supports built into them, they would rather you put your weight onto those supports.

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    DIY Junior Member patrick1's Avatar
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    Oh I see, thanks for the info! There is about a 6 by 6 inch area under the the where I didn't put mortar since it was so close to the drain but looking at it from under the house it wont affect the drain at all should I mix a little bit of mortar and shove it into that void?

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    DIY Senior Member dlarrivee's Avatar
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    Whatever gives you peace of mind.

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    Test, Don't Guess! cacher_chick's Avatar
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    Quote Originally Posted by dlarrivee View Post
    Portland cement doesn't mean lime...
    I don't claim to know it all, but common Portland cement mortar used for masonry has hydrated lime in it. If you are thinking of some other product, so be it.


    Can you show us where every manufacturer follows Kohlers suggestion of "masonry" mortar, or even just Kohler's?
    I don't care to spend the time trying, even if I could.

    I was making a general statement to say that there should not be any problem with using the product that the OP used. I have some experience in building with fiberglass laminates, and I believe that what works as a bedding material for a plastic composite shower or tub should work fine for a fiberglass one also.

    I am aware of likely problems is one uses plaster or other gypsum-based mortars, but that would be another topic.

    No worries- I'm here to learn.

    I guess I could have just asked, but I was trying to lead you to explain why you might believe that the product that the OP used is a problem. If you can teach me something that I can research and find to be fact, then I will be all the better for it. )

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