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Thread: Type S Mortar bed for tub

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  1. #1
    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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