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Old 06-15-2018, 06:35 AM   #1
iownme
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deck mud problem

Hello members
First time poster but i do read a lot here.

I have a problem with some deck mud i recently made.

I left it for a few days to set and found that i can scrape out some quite large and deep chunks with my fingers. By large i mean 4" round, 3/4" deep or smaller.

Also the mud is more brownish than my previous grayer mixes

i have successfully made 2 pans before this.

i mixed batches of 30lb sand topping with 15lbs play sand.
i used approx 1.25qts water.

I well mixed the sand topping and sand before adding water.

The mix was quite dry when done

Any suggestions as to why this is happening and how to fix it?
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Old 06-15-2018, 07:24 AM   #2
Carbidetooth
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Looks like not enough cement or perhaps too little water.

Recently, I went to pick up some "floor mix" which is, I think, a somewhat regional 5 to 1 mix I get at local Dal Tile. They told me that the last batch was shy on cement and that they were waiting for replacement inventory. I went back to my old standard of what you describe with Sand Mix and sand.

All that said, perhaps the Sand Mix you got was somehow also shy on cement. FWIW, I've never measured water, so I can't help there. I eyeball it. Unfortunately, I think you've looking at a do-over.
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Old 06-15-2018, 07:50 AM   #3
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Yep, what Peter said. Either not enough water or cement. Also, when you are finished shaping it, slick it down with the flat side of your trowel. If the water is just right, it will bring a little moisture to the surface giving it a slightly harder crust on top. This keeps it from eroding so easily.

Keep in mind that it's dry pack, not concrete. It's not designed to get rock hard. It's pretty cheap, I'd bust it up and start over.
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Old 06-15-2018, 09:10 AM   #4
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Also, a strategy to give the deckmud additional strength after installation is to spray a thin mist of water over it (once the cement has started curing, obvious, you don't want to wash it out of the mix) and then putting a plastic sheet over it for a day or two. Keep adding a little bit of water mist as needed. That will help the cement cure better.
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Old 06-15-2018, 10:17 AM   #5
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Also, if you know it's going to get a lot of traffic before it's tiled, vacuum the mud and apply a skim coat of thinset over it. This will help it last longer. Then cover it with a piece of old carpet or cardboard while working on it.
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Old 06-15-2018, 10:33 AM   #6
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thank you for the quick responses.
i did forget to mist after i laid the pan i think.... at least i dont remember misting....i used a mister when i added some extra deck mud but cant remember if i misted the entire pan. (i did on previous pans)
do you all really think it needs to be redone as opposed to filling the low spots with thinset?
i didnt add any cement as i used the deck mud calculator on this site, which said to use the sand/topping+sand.
i used quikrete sand/topping mix and quikrete premium play sand.
if i re-do the pan, what should i do differently to avoid this crumbly situation?
is anyone familiar with the youtube channel " so thats how you do that" ?.....
its his video ive used for the last 2 paintable membrane pans i made....this one is the same style
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Old 06-15-2018, 03:24 PM   #7
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Yes, I would do it over. I think that's too deep to fill with thinset. Measure carefully and you can add a little more Portland than you did the first time, but not much. I would add a little more water too. After doing it over, if you feel like it needs it, spray the mud with a light mist for about 10 seconds with a garden sprayer and then slick it with a flat trowel.
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Old 06-16-2018, 06:59 AM   #8
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i didnr add any cement as the deck mud calculator on this site doesnt mention anything about adding cement.... so am i adding cement too?...if so how much cement do i add to 60lb sand/topping mix and 30lb sand?
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Old 06-16-2018, 08:51 AM   #9
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Deck mud is just sand and cement (typically 5:1 to 4:1). Sand topping is also just sand and cement (typically 3:1).

So sand topping mix has more cement in it than is desirable for deck mud, it is too "rich". That's why you're adding extra sand.

If you feel that you've ended up with too little cement, then just reduce the amount of sand you add to the topping mix. No need to add more cement.

60 lbs topping mix is 45 lbs sand and 15 lbs cement. With an extra 30 lbs sand, that's 75 lbs total sand and 15 lbs cement, or 5:1. If you want to go to 4.5 : 1, then you'd need to add just 22.5 lbs sand to 60 lbs topping mix.

Cheers, Wayne
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Old 06-16-2018, 10:28 AM   #10
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thank you wayne for that excellent explaination.

I just finished tearing out the pan.
I was shocked at how easily it came out.
Removal took about 10 mins.
There was zero bond to the walls or floor.
Does the attached pic look like not enough water or a bad batch of sand topping?.
My tile guy says he likes to use a premixed sand topping product for morter beds, what is the benefit of that?
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Old 06-16-2018, 10:49 AM   #11
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Welcome, Fred.

New deck mud should come out that easily and it isn't expected to bond to anything on its own. If you want it bonded to something, such as a concrete subfloor, you use a slurry of thinset mortar as a bonding agent.

There shouldn't be any CBU on that shower floor. What is your planned waterproofing method for this shower?

Given that you have CBU on the floor, I'm guessing that floor is wood framed, yes?

As for your deck mud being as soft on the surface as it appeared in your photos, I would suspect it wasn't properly packed before shaping. I've experimented with various mixes and amounts of water and have always been able to get a useful mud bed so long as it was properly packed. Lack of packing before shaping would result in what I see in your photos.

But let's discuss your shower receptor construction method before you start a new mud bed, eh?

My opinion; worth price charged.
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Old 06-16-2018, 10:59 AM   #12
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If guessing, I'd lean toward too little water and/or not packed sufficiently.

Your photos lead me to ask: Tile backer under pan? I wouldn't expect dry pack to bond to it as is. Assuming you wanted a bond, a thinset slurry would be needed but that would beg the question, why backer on floor and how is it attached to whatever is underneath?

I assume your "tile guy" uses similar to what I mentioned above. It's a one bag solution and that just simplifies things. Either would work fine.

As an aside, I should mention that the permeability of mortar above liners is of no real concern to me because I only use surface membranes. Consequently, I make my mixture a little cement rich and perhaps wetter, which makes it easier to slick down. I always cover with plastic till at least next day, more if I can manage it. This probably comes as a result of knowing how concrete cures, which I had experience with before I ever tried my hand at shower pan construction.
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Old 06-16-2018, 12:05 PM   #13
iownme
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ok, so my method of construction is taught by a man who runs a tile/laminate university to which i belong and is complimented by a youtube channel and facebook channel, all named "so thats how you do that"

there is no liner, he recommends making the mudpan in the fashion you saw in pics, and then painting 2/3 coats of hydroban then tile right on the hydroban.

i have 2x3/4" ply under the cement board and the cement board is screwed down in a grid fashion every 5" with cement board screws
The entire bathroom floor is done the same as it will be tiled also.

It is a wood framed, 2nd floor room.

yes, tile guy uses a one bag solution which i imagine is a 5:1 mix (waiting to hear back from him about that)

I feel i packed it well but im no pro so i'll accept that perhaps not well enough if thats what you advise

As for the "bonding"
I have no expertise in cement products and i just thought it was supposed to bond to the floor/wall.

As stated previously, this is my 3rd shower with a paintable surface membrane and this current one is with a previous customer in his 2nd bathroom so i must be doing something right...haha.

being a bit of a perfectionist i do like to learn to do things right so your advice is not wasted
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Old 06-16-2018, 12:09 PM   #14
iownme
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this is the previous tile work i did in this house.
that shower is 5'x7'
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Old 06-16-2018, 12:12 PM   #15
iownme
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another question
the store sells 2 types of quikrete sand, play sand and another.
What is the difference and does it make a difference in this application?
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