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I am really confused. I've read numerous posts that say that using Type-S mortar for shower bed is a no-no. I called Sakrete, and they confirmed that it's not for shower bases and more for laying brick, etc. Then I called Oatey to inquire what shower base should be made of to install their shower liner and the rep told me that I can use Type-S mortar. Who is right here?

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Type S mortar is mixed really wet so it would be hard to shape it into any sloping shape and it better for thinner applications, like brick laying. If you mix it dryer that instructions say, you take the risk of it crumbling.

I'd be following the advice from the manufacturers of the mortar over the advice from the manufacturers of the products going on top of it.

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  • The Sakrete people correctly discouraged the use of type S masonry mortar for preslope and mortar bed. The Oatey people correctly encouraged the use of type S masonry cement for mixing a suitable mortar. There is no contradiction between the two.
    – popham
    Commented Oct 23, 2023 at 21:55
  • @popham Not sure what your point is. The OP never mentions anything about type S cement, only type S mortar.
    – JACK
    Commented Oct 23, 2023 at 22:53
  • Type S mortar is type S cement with sand in it. Your answer is calibrated for type S masonry mix, not for type S mortars generally. Just because this particular type S mortar was unsuited to shower work doesn't mean that all type S mortars are unsuited to shower work.
    – popham
    Commented Oct 23, 2023 at 23:06
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There's type S mortar and type S mortar cement. Type S mortar is type S mortar cement premixed with sand. When the bag says that the mortar is for masonry (like you'll typically find at the hardware store), then that means that they mixed 2.25 to 3 parts sand to 1 part type S mortar cement (see https://www.quikrete.com/pdfs/data_sheet-masonrycementtypes.pdf). I think that Oatey used to specify 4 parts to 1 for the preslope instruction with their liners. Now they leave the mix unspecified, where I suspect that they got tired of answering the phone for people advised to do something else. Lots of people swear by 5 parts to 1. Splitting the difference, let's say that the ideal ratio is 4.5 parts sand to 1 part type S mortar cement. To achieve that ratio, you'll want to add 1 part sand to 2 parts type S masonry mortar mix.

Reasoning:

Assuming a type S masonry mortar mix with (2.25 + 3)/2 = 2.625 parts sand to 1 part type S mortar cement, you'd add 1.875 parts sand to the (2.625 parts sand + 1 part cement) = 3.625 parts of type S masonry mortar mix to get 1.875 + 2.625 = 4.5 parts sand to 1 part cement. These fractions clean up with multiplication by 8, yielding 1.875 ↦ 15 parts sand to 3.625 ↦ 29 parts type S masonry mortar mix. 1 part sand to 2 parts type S masonry mortar mix therefore provides a good approximation to achieve the 4.5 parts sand to 1 part type S mortar cement.

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Type S Mortar is great for shower pan and pre-slope pan only if you mix it as dry pack. It bonds very well with small amount of water.

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    Commented Oct 23, 2023 at 15:55

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