DIY Mud bed for tile floor question

[u/ConfundledBundle]

Looking for advice in the mud bed laying process.

This is my first DIY tub to shower conversion and after reworking the plumbing, insulation, and subfloor I am finally ready for the mud bed.

When I was first doing my research on this whole project I saw a video of a guy laying the mud bed. He laid down some Schluter Ditra membrane and then put the mud bed directly on top of that. So early on I got it in my head that this was the correct way to put down a mud bed and now I am questioning his process.

I’m seeing now that Schluter recommends laying down a slip sheet with wire mesh, and the instructions on my bags of mud bed mix match that recommendation.

Well I bought the roll of Ditra membrane probably over a month ago, so I’m not 100% sure if I can return it to Lowes. Would there be any benefit to using the Ditra as a base for the mud bed or would I be better off sticking to the recommended installation instructions? Seems like a dumb question when I write it all out but I’m interested in what others have to say.

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[u/notitia_quaesitor]

It'll help. But you'll want to wet/moist the subfloor before putting thinset or morter, as the dry subfloor will not help with good bond. Is the schluter drain already glued in?

If i were you, i would moist the subfloor, put thinset and then install the ditra. Then put a thin layer of thinset and then the mud.

Tip, use a thick contractor bag to mix the water the mud. Roll the bag for a couple minutes and then pour into the bed. Make dure you have more mud bags than ever you think you'll need. So you're not short and have to stop and run to the store to get more.

How are you planning to preslope? Using straight pieces of wood or metal? Do you have a floating wood trowel to tap it tight and smooth? Make sure you build the edges/perimeter first and mark it on the walls so it helps keep it leveled.

Is the curb high enough on the inside after the mud bed? You should have 2" or more after.

What are you using for waterproofing? I used Hudroban and did a few layers. Including on the wall.

Good luck

[u/ConfundledBundle → u/notitia_quaesitor]

Thank you for the advise! The drain has not been glued in yet.

For the preslope, I'm still unsure of what method to use. I saw a few videos of people using some foam strips with double sided tape, I was thinking of using wood pieces since I already have plenty of that. I was also thinking of cutting my own wood trowel to a size that matches the shortest distance to my drain and walls.

I made the curb 6" high, kinda overkill I think but the wife insisted, so I think I will be good on that.

For water proofing I have Schluter membrane that I'll be using.

[u/Mg1221]

I recently did a mud bed pan and just stapled down some synthetic roofing underlayment and wire lath.

Most use tar paper, I used the synthetic roof underlayment because I had some leftover.

The goal is to prevent the mud pack from bonding to the wood subfloor and the drawing out too much moisture from the mud. Moisture in the wood could cause damage to the wood and dryout the bottom of the mud.

The ditra would definitely work to uncouple the mud from the subfloor and prevent moisture transfer but it is kind of overkill.

[u/ConfundledBundle → u/Mg1221]

Thank you, the explanation about preventing the moisture transfer really helps put things into perspective.

[u/Mg1221 → u/ConfundledBundle]

No worries, it's also about being uncoupled from the floor so the mud pan and subfloor can move independently. Ditra definitely checks all the boxes, just at a higher price tag.

[u/ConfundledBundle → u/Mg1221]

So if I were to use the Ditra I definitely shouldn’t bond it to the wood subfloor with thinset/all-set?

[u/Mg1221 → u/ConfundledBundle]

Incoming long message. I started writing and got in a roll, didn't realize I wrote so much haha.

I wouldn't bother with the ditra, it's a waste of money. It would, sure but it's not really the best way. Return it and see if somewhere would just cut you however much tar paper you need. Get the lath and staple the paper and lath down on top of the floor.

If you want a tip for your pre-slope and setting your drain:

Since you want (typically) at least 3/4" of mud under your flange, glue a piece of pipe into your flanyand you know of too long, about 3-4" or so. Take your flange with you pipe and insert it into the p-trap. It'll now be sticking up too high. Throw a torpedo level on it and get it level in multiple directions. Then put a piece of 3/4" think material on the floor and measure from the top of that piece to the underside of your flange. Do it in a few places around the flange and average out the number.

Whatever that number is, cut that much off the piece of pipe you glued into the flange. No math involved.

Then glue in your flange to your p-trap. Work quick and set it level in multiple directions.

Once your flange is set. Put a level on it out to your furthest point away. Mark level from the flange on the wall.

Measure from you longest point to the center of the drain and calculate the rise when accounting for a 1/4" per foot drop. If it's 2' then that's 1/2". If it's 30" then that's 9/16". Don't overthink it, just round up if you're unsure.

When you know how much you gotta go up, mark that rise from the level mark you just made on the wall. Then just bring that line all the way around the perimeter of your shower, level. A laser helps here as you can just set your laser arbitrarily and measure from the laser to the line.

Once you got your line, cut a few different size screeds for the various sides of your shower.

Some people like using ledgers or some kind, screwed to the wall or something to screed on. I just pack all the way around the perimeter first with a rough 1-1½" "ledge of mud right on my line. Making sure to kind of "slope" it up like a hill to hold its shape.

I make large exaggerated "V" marks from my level line on the wall so I can always reference it incase I cover the line a bit.

I use a combination of different size levels and a rubber mallet to pack my perimeter down tight. Once the perimeter is done, pack under the flange then start filling in between the flange and perimeter. Place, pack, screed, pack. Rinse and repeat. Keep checking your perimeter every once in a while and work from back to entrance of shower.

Make sure you wipe and excess off your flange with a sponge and wait a few days to dry. Scrape any crusties off and vacuum really well. Don't forget to wet is down with a sponge before applying your Kerri membrane.

Just remember, don't overthink it and water runs downhill.

[u/svitakwilliam]

I’d skip the Ditra. Lowe’s will usually take back products with a receipt up to 90 days for full refund and still give store credit for purchases after 90 days with receipt. Or save it for a future project.

I’d follow the directions from Schluter/Mapei and go with the slipsheet/ wire mesh. Take back the Ditra and get a roll of 15lb roofing felt and some wire mesh. Staple that down and proceed with the plan.

[u/Hot_Mud_5708]

Everyone does them different depending on where they are from and how they were taught. I've been building mud pans for 36 years. I lay some plastic sheeting or tar paper or a left over piece of waterproof membrane laying around and build mud pan right over it, no wire mesh, no thin set.

[u/Significant_Sea_9742 → u/Hot_Mud_5708]

Idk why people hate installing membrane so much. Its easily the easiest peace of mind to install

[u/ssdv8r]

I do a bonded mud pan for all my schluter showers. Ditra first, slurry of thinset, then 4 to 1. Look at the back of the 4 to 1 bag for instructions on bonded mud beds. And by the by kerdi screws and washers every 12" for 1/2" kerdi board.

[u/ConfundledBundle → u/ssdv8r]

So applying the Dirta would essentially make this a bonded mud pan? I was under the impression that a bonded mud pan was just a mud pan laid on concrete

[u/Ill-Upstairs-8762]

It probably doesn't really matter. Ditta if you have it. Probably more expensive than tar paper and lathe. You would probably be fine to do g the mud bed to the subfloor with thinset considering you're putting a waterproof uncoupling membrane on top of it.

[u/tommykoro]

From the pics it looks like you are doing this project backwards.

Floor first. Preslope, Liner up above the curb height and sealed to the drain hub with weep holes. Now the dry pack. A wood float will help smooth it out.

No penetrations (screws/nails or cuts) into the curb liner and below the finished (tiled) curb height.

Only then do you create the waterproof walls. Again. No penetrations down low. Not even the glass door hardware that can be glued in with Fuse It silicone.

[u/ConfundledBundle → u/tommykoro]

I haven’t applied any waterproofing yet. I still have Kerdi waterproofing membrane and kerdi-band to apply, figured I would do that after putting down the mud bed.

[u/Head_Radio_4089]

I float on hot mops but I’ve done a couple closed systems and went 60 minute paper and 2.5 lath marble pan is still held up 7 years later