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Unread 10-19-2020, 08:28 PM   #1
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Deck mud or self-leveling underlayment?

Hi everyone,

I'm in the process of tiling our small 16 sq. foot powder room (no tub or shower) and am hoping to get some guidance. For better or worse this is my first time working with tile -- hopefully I'll be using the correct terms but if not, hope I'm close!

I removed the mosaic tiles that were in place but the mud bed underneath was cracking and flaking so I decided to remove it as well. Now I have an exposed cement slab and some pretty big gaps to fill (in some spots, about two inches) in order to get the floor back up to its original level. I attached a pic below.

I've been watching Isaac Ostrom's very helpful videos (YouTube "Tile Coach") on creating a deck mud bed AND using self-leveling underlayment. My question is, which should I use for this space -- the deck mud bed or self-leveling underlayment? I'm a one-man band here so I'm concerned about being able to prep enough self-leveling underlayment to fill in that space without the risk of the last batch drying.

Another question -- in one of his videos (https://www.youtube.com/watch?v=dQw5d9sdz48), Isaac places Aquabar tarpaper and stucco netting on top of the concrete slab prior to filling in with the deck mud. I presume I should be doing the same for my application -- does that sound correct?

Thanks in advance -- any input would be greatly appreciated!
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Last edited by etudenc; 10-19-2020 at 08:53 PM. Reason: (correcting terms)
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Unread 10-19-2020, 09:06 PM   #2
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A bonded mudbed would be your least expensive, and maybe easiest choice to raise the level where you want it. With the volume you need, you might want to rent a cement mixer. Over a slab, I don't think you need any lath or reinforcement wire. A slurry of cement on the slab, throw the deck mud down, spread it out, screed it off to get things about the height you want, pack it down, trowel the surface to bring up some 'cream' and maybe cover with a plastic sheet for overnight (as we get into the heating season, the humidity levels drop, and you want the cement to cure, not dry out before it gets the chance).
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Unread 10-20-2020, 09:28 AM   #3
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Thanks much for your reply! RE slurry of cement, could I also use a concrete bonding adhesive in place of the cement slurry?
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Unread 10-20-2020, 09:51 AM   #4
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"Concrete bonding adhesive" is usually something similar to Elmer's white glue, Phil. I'd recommend a slurry of of thinset mortar or Portland cement. The Portland slurry tends to dry very quickly and the thinset mortar slurry remains wet longer and is generally easier to use. Entirely up to you, of course.

My opinion; worth price charged.

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Unread 10-21-2020, 08:25 PM   #5
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Thank you, Cx, that's helpful! I'll probably go with the thinset mortar as I'm sure the extra drying time will come in handy.

I appreciate everyone's input, thank you again!
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Unread 10-22-2020, 11:40 AM   #6
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A few tips for that bonded mortar bed (should you decide to go that route):
  • We suggest using a polymer-modified mortar for the scrub/bond coat.
  • Make sure you mix whatever mortar you choose for your scrub coat on the wet side of the water ratio.
  • Use a notched trowel to apply the scrub coat as if you were setting tile.
    i.e. flat trowel the substrate first, and then come back and notch the material with the serrated side of the trowel.
  • "Prime as you go" by troweling out the mortar as far as you can pack the bed in it at a time.
    It's important the mortar is tacky and doesn't "skin over" before you can get the deck mud packed into it.

I hope that helps!

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Unread 10-22-2020, 07:08 PM   #7
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I seem to post this picture a lot.

With the base already set, you can notch a stick the tile thickness and use it to pull the mud, leaving just enough space for the tile to slide under.
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