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Unread 09-21-2021, 07:50 AM   #1
mikeylouca
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mortar shower bed

I just tore out my old shower which had mildew and water penetration below the old liner. The liner was directly on the slab with no preslope and mortar on top of the liner only. As I am researching how to re do this, it appears that it is inevitable that water will leak through the grout and tile to the mortar, which when presloped will allow the water to wick down to the weep holes to drain. This seems like a built in recipe for more mildew to grow, i cannot believe all the water will wick out fast or completely enough to prevent mildew. Can I use silicone sealant instead of sanded grout to seal the tile? My drain is off center so I cannot use a plastic shower pan and shower wall assy without centering the drain. This tiling thing appears silly to me. Am I missing something?
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Unread 09-21-2021, 08:06 AM   #2
cx
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Welcome, Mike.

The traditional mud/liner/mud shower receptors have been used for many decades and, properly done, work just fine throughout their lifespan.

There is nothing in the construction materials that can provide food for mold growth, and, when operating as designed, they are a water-in/water-out system and never hold the same water, containing potential mold food, long enough for a problem to develop. That and evaporation back up through the tile surface keeps them functional for generations.

Your shower receptor, on the other hand, with the waterproofing membrane flat on the subfloor, where the water must actually flow uphill to reach the weep holes in the drain, can hold the same water for very long periods. And that water will contain body oils and all the soaps and such used in shower activity. Those substances, given the long-term wet and sufficiently warm environment, can allow for a lot of mold growth. That's the reason for the pre-slope required by both the plumbing code and the ceramic tile industry standards.

Build one of those receptors correctly and you should never expect a problem. You try sealing the tile surface and you'll still get some water down into the top mortar bed, it just won't be able to dry through the tile surface as would normally be the case. I recommend you don't do that. Use a cementitious grout and your shower should outlast you.

If you still don't like the idea of the water-in/water-out system, try one of the newer direct bonded waterproofing membrane systems. They eliminate that "feature," but do come with some other considerations.

My opinion; worth price charged.
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Unread 09-21-2021, 09:11 AM   #3
mikeylouca
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Thank you CX, I feel better about it now. Should I use cementitious grout with any acrylic additive or just plain?
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Unread 09-21-2021, 09:24 AM   #4
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I recommend you add whatever the grout manufacturer recommends and only what the manufacturer recommends.

Others on here will make different recommendations on grouts for your shower and you must decide for yourself what's best for you.

My opinion; worth price charged.
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