Mortar under shower pan - new question

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TorontoTim

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There have of course been many discussions about mortar, Structolite, expanding foam, roofing felt and other sorts of product used under tubs and shower pans.

My question isn't about whether to do this or not, but rather if I chose to, could I in my situation.

I'm doing a 3 piece bathroom at our cabin. Nothing special - I put classic black and white Armstrong VCT on the floor with the intent of using a 100 year old cast iron tub we had.

Upon sober reflection, older parents planning visits and thoughts of ourselves 20 years down the road, the notion of showering in a clawfoot tub became less appealing. No room for a shower and tub, and my better half doesn't like more modern tub/shower combos, so a simple shower stall is going in.

So here's the question. In all the discussion of using a cement type product under a shower pan, I haven't found any mention of the importance of adhesion. People in fact have talked about putting a layer of plastic between the shower pan and mortar to make removal easier.

I'm dealing with a fully installed and waxed VCT floor. I like the idea of a secure solid shower pan (I used a cultured marble pan in our basement bath set in thinset directly on the slab and it's awesome), but I'm dubious as to the value of using mortar or Structolite on top of the VCT.

Of course, adhesion to the showerpan is not likely either, given it's solid acrylic (Vikrell). And the pan is highly webbed with many feet and sits solid on the ground already. So it's not critical. I might just throw down a piece of roofing felt and plop it down.

But, if I chose to use mortar, is adhesion to the floor important? I'd hate to have crunchy product under the showerpan because it's not 'stuck' to anything.
 

Jadnashua

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Sorry I didn't see this earlier...

The advantages of mortar underneath a pre-made shower pan are that it can help level it, if the floor itself isn't already level, and, if there is any flex to the pan, it can provide 100% support (or close, depending on the shape of the thing). It really is not to anchor it in place.

So, you'd want to set the thing in place and see if it moves or flexes...if so, then something underneath will help. Many fiberglass and acrylic pans almost beg for this, otherwise, they get stress cracks and can fail. In the interim, those cracks start to look nasty and are impossible to clean and keep from staining. If yours is solid enough, is level, and doesn't rock or flex, you don't need anything, but follow the manufacturer's instructions.
 
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