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Unread 09-21-2022, 11:09 PM   #1
Flintluck
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Shower Mud Bed Tear Out?

I've been a lurker for a couple years now learning a lot from this forum. The knowledge I've learned has been invaluable. The internet can be wonderful in the right applications.

On to my question - I am working on installing a shower for the master bathroom and opted for a mortar bed for my shower pan since my 3'x5' shower is slightly offset from the drain, which is buried in the concrete slab. I am using a Schluter drain and finished putting down Mapei's 4-TO-1 MUD BED MIX on Monday at 4pm at a 1/4" per foot slope down to the drain, which was placed at 3/4" above the slab per recommended thickness for the bed. I noticed the next day that there was a significant amount of grain on the surface but let it sit to cure for another day. Today, I swept and vacuumed the pan and saw some uneven spots.

I used a 6in tape knife to scrape out any spots that seemed like they could crumble or were a slightly different (darker) color than the rest of the pan. I believe this could be because I mixed 1 bag and packed all the edges. I then mixed two more full bags at the same time and packed them to fill the middle. I also soaked some of the mud to stuff it up under the drain. The bag said the pot life was up to two hours, which I definitely took.

I'm thinking I might have waiting to long and not packed some of the second batch enough as a couple of the darker areas sounded hollow. I used a crowbar and mallet to chisel out those areas that sounded porous. In one spot, I've reached the slab. Everything else has a 1/4" to 1/2" deviation but is pretty rock solid. The small drain holes around the edges appear to have mud that's a bit loose but it doesn't give when standing on it. I can definitely scrape some of the dried mix out if I tried though. Regarding the pan, I've walked, jumped, kicked, etc. on the bed and it seems solid.

So finally my question - should I tear this out and start over? If so, what's the best tool to get it out and save the curbs and drain?

Or do you think this is salvageable and I can get more mud and throw down a bit of thin-set in the hole to bond it to? Same with the edges of the drain?

I want to do this right. My main concern is how to properly get the mud bed out if I need to tear it out as I does seem a large portion set well.
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Unread 09-22-2022, 05:28 AM   #2
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Hey Johnathon, My first question is did you bond the mud to the slab? Also the drain is usually bonded to the mud as well using thinset mortar did you do that?

The best way to get the mud out is usually just hitting it with a small sledgehammer to break it up and/or a prybar to work it underneath if you didn't bond it. The drain you'd be more delicate around, being plastic the mud should release fairly well from that. Scraping with a cold chisel or something similar.

The best part about a good thinset is it bonds really well, the worst part is it bonds really well and is a pain to remove.
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Unread 09-22-2022, 06:32 AM   #3
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I didn’t put thinset on the drain itself. I put some under it and did thinset the edges thoroughly. I didn’t get as great coverage in the middle as I was getting some of it mixed with the mud after I set my edges and started working in. The one spot I dug out does have little thinset on the slab.

Would a 10lb sledge be good to redo here?
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Unread 09-22-2022, 08:52 AM   #4
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Hi Jonathan,

Loose the 10# sledge. They only use those on TV.

I would first go over the entire mud bed with a shop vac. That'll tell you whether it's repairable. Show us another picture after you've done that.
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Unread 09-22-2022, 11:48 AM   #5
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Appreciate the feedback! If needed, I'll take a cold chisel to it.

I've uploaded a few more images here. Just swept and vacuumed everything.
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Unread 09-22-2022, 12:34 PM   #6
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While I think it possible to "flash patch" this job....floor mud is cheap and my vote would be to remove it and go again. The 4 to 1 is decent and I use it frequently. Look at this as a learning experience or a first trial.

With Kerdi, you want a pretty smooth base to set the membrane. After it has set, use a "rubbing stone" to smooth out the top...
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Unread 09-22-2022, 01:16 PM   #7
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Okay, sounds good. Would a flash patch basically be thin-set and packing additional mortar?


To tear it out do I need anything other than the cold chisel? And should I buy the same pre-mixed mud? They're about $23 each, and I'll need four of them.
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Unread 09-22-2022, 03:51 PM   #8
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Yeah, I would tear it out. Dal Tile has it for about $10 a bag...
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Unread 09-22-2022, 08:36 PM   #9
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OK, great. I’ll tear it out and start over! I live near north Austin in Georgetown and wasn’t able to find a Dal Tile location online with pricing for Maipei 4 to 1 like you referenced. Is that something that only available in stores, or is there another mix that would be preferable for a cheaper budget??

And do I need anything other than a cold chisel for this? There is definitely thinset on the base of the majority of the floor. I do have a grinder I can use than I removed the rest of the bathroom tile with if necessary.
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Unread 09-22-2022, 08:42 PM   #10
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Welcome, Jonathan.

I'd recommend you use a sand/cement mix rather than the MAPEI material. Easier to work with, less expensive.

If you have some Portland cement and sand available, 5 sand and 1 cement is a fine mix. If you must use bagged products, look at the Shower Construction thread in our Liberry and scroll down to a post showing how to make the same mix using bagged products from your home center.

A cold chisel and medium pounder should remove the old mortar bed.

My opinion; worth price charged.
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Unread 09-23-2022, 10:35 AM   #11
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I’m working on the tear out now - edges are tough! Gonna rent a bigger chisel from HD as my little one isn’t quite cutting it.

I read through the articles on mud that you mentioned and had a couple questions.

If I buy 120lbs of sand topping mix, it looks like mixing that with a single 50lb bag of play sand will be enough since the article referenced 60lb mix + 15-30lb sand. Or should I buy extra sand to add another 10lb?

Also the article mentions needing to complete everything in 45 minutes. Is that the entire bed including the mixing, packing, and leveling? Or can I mix small batches at a time focusing on packing the edges first and screeding everything at the end? What’s the best method to wet about a bucket at a time?

I think the whole job will take me a couple hours. I know last time my mud was probably too wet. Just want it to be right this time
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Unread 09-23-2022, 12:21 PM   #12
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Jonathan, consider that the Sand Topping Mix is presumed to be a 3:1 sand to Portland cement mix, and what you want is about a 5:1 mix. There is no rocket surgery involved here. Your mix can be anywhere from 4:1 to 6:1, but 5:1 is a good mix with plenty compressive strength and is easy to work. I know I don't like 4:1, even though that is actually the ANSI recommendation, and I've never gone as lean as 6:1. The 5:1 works well and I recommend you get as close to that as you can.

As for timing, treat it much like keeping a wet edge when painting, if you're familiar with the concept. Be well prepared and mix as you go. If you're working alone I very strongly recommend you invest in one of these Bucket Mortar Mixers. Gather enough buckets to dry-mix enough material for your entire floor and stage them near the shower. Make a water container that will hold exactly the correct amount of water (you'll have experimented with one bucket and measured the water carefully). Add water and mix each bucket as you use them. Takes less than 2 minutes to make a new bucket that way. Or get a helper to mix for you as you work.

Mark a level line around your shower perimeter at the correct height for your mortar bed. Pack mortar solidly up to that line for a perimeter "screed" to work from. Continue doing that and filling in between the screeds and packing and shaping 'till you've made a shower floor. Even a fairly large floor can be done in less than an hour working alone if you prepare well and work steadily.

My opinion; worth price charged.
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Unread 09-24-2022, 02:12 PM   #13
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Pan tear out was a success. Was a cinch with a 20lb hammer, and then I used my angle grinder to knock out the extra thin set. I was able to save the curbs and the drain.

I am going to divide the sand and cement mix into three separate 5 gallon buckets this time and track how much water I add from the first bucket for the next two. Bought a stir paddle too. I think this time it’s gonna go a lot better. I will let you know how it turns out!
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Unread 09-24-2022, 02:44 PM   #14
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Quote:
Originally Posted by Jonathan
Was a cinch with a 20lb hammer,..
Good lord, man, I don't think John Henry's hammer was that heavy!
Quote:
Originally Posted by Jonathan
Bought a stir paddle too.
Not many designs I've seen will work well for mixing deck mud. Actually, the total number thus far is one.

My opinion; worth price charged.
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Unread 09-24-2022, 09:06 PM   #15
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I use a wheelbarrow and a hoe, then shovel into buckets. 100 lbs is what I have mixed at once which is approx 2.5 five-gallon buckets. Probably enough for half of a 60 X 32" shower....depending on a few factors.

Your screed stick material.....cut yourself a number of different lengths between your longest dimension and shortest (perimeter to drain length) and have them handy as you are tamping and screeding. For a rectangular shower, I find that 4 different lengths work for me. I'm sure pros can do it with eyes closed but from a DIY'er prospective, I need the different screed lengths.

Set your perimeter, add mud where low between perimeter and drain, pack and screed, add, pack and screed then pack again. Check with screed, "add/pack/screed/pack" as necessary to have a perfectly flat slope to the drain, no matter where that flat screed runs from perimeter to drain.
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