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Unread 08-03-2022, 04:58 PM   #1
bradyc5562
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Thinset under Preslope on concrete slab and more

I’m doing a shower on concrete slab and I need to do my pre-slope next. I know I need to do a coat of thinset on the slab before the preslope mortar. Does that thinset need to be modified or unmodified? And the drain is very close to the slab so the pre-slope needs to get very thin as the reaches the drain. I’ve heard I need to add quickrete concrete acrylic fortifier to the preslope mud mix to be able to get that super thin near the drain. Is that true? If I do use the acrylic fortifier in the mud, it says on the bottle “is not to be used with polymer modified products” would that react with the polymer modified thinset(if I need to use modified)?? Thanks guys!
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Unread 08-03-2022, 05:27 PM   #2
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Welcome, Brady.

There is no ceramic tile industry standard for shower pre-slope mix, because that pre-slope is part of your plumbing. The tile industry does require that you have the pre-slope, though.

Deck mud/Dry-pack/floor mortar is what's generally recommended by the tile industry for making the pre-slope. The minimum thickness generally recognized by the tile industry for such mortar is 3/4s of an inch.

If you're not prepared to raise your drain to the proper height, you'll just need to do the best you can with the mortar you intend to use and hope for the best. Making the mortar a good deal richer (more cement) and a little wetter near the drain might help. Or not.

As for bonding the mortar to the concrete, you can use modified or unmodified thinset mortar or even just pure Portland cement. The modified mortar will be the easiest to use and you'll need some of that for the rest of the project anyway. You'll mix that into a slurry and apply it to the concrete immediately before placing your deck mud while the slurry is still wet.

You can mix your dry-pack with some polymer modifier if you want, but I wouldn't bother.

My opinion; worth price charged.
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Unread 08-03-2022, 06:00 PM   #3
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The modifier makes it harder to form as it then becomes sticky. Too much water in concrete makes it weaker and subject to shrinkage cracking.
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Unread 08-03-2022, 06:17 PM   #4
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If your mud at the drain wants to crumble the next day, remove it from that area where it's too thin and use straight thinset. Thinset is good from 0 to about 1/4 inch thick.
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Unread 08-03-2022, 06:25 PM   #5
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Thanks guys. CX these 103F temps need to calm down huh!? OK, well it sounds like the plan is going to be: modified thinset (versabond) slurry under the dry-pack (around 4-to-1 mix) and DONT add the acrylic fortifier..... hmmm, Does it make sense to have a little bit more of thinset at the drain like this (see pic) to help the mud to drain transition because drain is so low? or just feather the dry-pack mud down the best I can?...
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Unread 08-03-2022, 06:26 PM   #6
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Davy, gotcha, kind of like this^?
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Last edited by bradyc5562; 08-03-2022 at 06:35 PM. Reason: forgot the ? "facepalm"
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Unread 08-04-2022, 05:22 PM   #7
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I would stop the preslope mud back about 6-8 inches from the drain and use thinset from that point to nothing at the drain. Avoid the little step at the drain.
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Unread 08-04-2022, 09:04 PM   #8
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Perfect, sounds like a plan. Thanks guys!
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Unread 08-17-2022, 08:22 AM   #9
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Best thinset for 18x18 Porcelain tiles in shower

hey guys what the best thinset for 18x18 Porcelain tiles in a shower? Its cement board and waterproofed with redgard. Using Home depot so they have the usual like standard "VersaBond" or do I need "Custom VersaBond-LFT" and Custom Natural Stone and Large Tile". Also should I go with white or grey. The tile is kind of a sand stone color and grout will be a grey or dark grey if that helps. Thanks in advance!
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Unread 08-17-2022, 08:25 AM   #10
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Versabond LFT or Prolite. Prolite has the better bonding strength of the two.

Gray is preferred in your scenario but white would work just fine too.
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Unread 08-17-2022, 08:51 AM   #11
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Brady, I've combined you with your original thread for this project for continuity and so folks can see what you're working on and what's been previously asked and answered. A moderator can give it a more generic title any time you'd like to suggest one.

You don't need a particularly strong bond strength for a shower wall application, so I'd recommend you go with the less expensive of the two James recommended.

My opinion; worth price charged.
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Unread 08-17-2022, 08:56 AM   #12
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Thanks I'll keep my posts on this thread. I'll go with Versabond LFT in gray then. Its cheaper and Prolite in gray is almost non existent around here for some reason right now. Any tips on mixing/using it (Versabond LFT being a Medium Bed Mortar) compared to thinset? Also can I use the Versabond LFT for the tumbled Marble pebble Mosaic on the floor or will I need standard thinset for those?
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Unread 08-17-2022, 09:09 AM   #13
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Brady, VersaBond LFT is a thinset mortar. There is no such thing as a medium-set method of installing ceramic tiles, nor does the industry recognize the term "medium bed" as a type of thinset mortar. The VersaBond is a Large and Heavy Tile mortar according to ceramic tile industry standards. It can be used in thicker sections than "regular" thinset mortars and has thixotropic (non-sag) properties. That's all why it says it meets ANSI A118.4HT, rather than just A118.4.

All that to say there ain't no medium bed mortars, regardless what any particular manufacturer wants to print on their bags or in their literature!

The mixing requirements should be printed on the bag. I haven't seen one lately, but if it's not on the bag (I'd be surprised), it's easily found online.

My opinion; worth price charged.
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Unread 08-17-2022, 09:19 AM   #14
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Haha wild. Thanks for the info! So what I'm hearing is basically it will look and feel (consistency) just like standard thinset? can I use the Versabond LFT for the tumbled Marble pebble Mosaic on the floor also (so I don't have to buy two different kinds of thinset)?
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Unread 08-17-2022, 09:28 AM   #15
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I have never used the LFT version of VersaBond, Brady, and can't really answer your question. I've been meaning to buy a bag just to see what it's like, but being a guy with no tiles to set, I've just not gotten a round tuit.

I'm sure someone will come by who uses the stuff and give you better information.
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