How to Make Deck Mud

by Roger

To create a shower floor from scratch we use what is commonly referred to as “dry pack mortar” or deck mud. Deck mud contains three ingredients: regular portland cement, sand, and water. That’s it. Don’t let anyone tell you that a latex additive or anything else is necessary. It is not. Properly mixing and installing deck mud will create a shower floor that will last for years and years.

The ratio is very important to achieve the correct consistency and stability. You want 5 parts sand to 1 part cement. Your ratio can vary from 4 to 6 : 1 but the 5 : 1 is what I use and find to be the easiest to work. You want just enough water to dampen the mixture. It’s not a lot. Too much water will cause your mud to shrink as it cures and compromise the stability of your base. You just want it damp – really.

The easiest and most convenient way to get your mixture correct is to buy the quikrete “sand and topping” mix which is sold at all the big home centers. This is already mixed at a 3 : 1 ratio. For a 60lb. bag you need only add 30lbs. of sand to it. This is how I mix mine – it’s convenient. The easiest way to mix it is with a regular shovel or garden hoe in a mixing box or regular wheelbarrow, although you can mix it with and in anything that works for you.

After it’s mixed it should just be damp. When you pick up a handful of it you should be able to squeeze it without water dripping from it. It should be able to hold it’s shape when you squeeze it, just like a snowball.

Whether you mix the entire batch from scratch or use the sand and topping mix it should all have this same consistency. If it is any wetter it will shrink as it dries and it will not be as solid and stable as it should be. I usually start with about 1/2 gallon of water and work up from there. I think. I really can’t tell you exactly how much water to use because I don’t measure it. I’ll have to do that and include it here.

As you install and shape your base, slopes, and shower floors you want to pound the mix with a wooden or magnesium float. I mean beat the hell out of it. You want the mud packed very well with no voids. The harder you pack it the more stable it will be. I have or will have individual posts to instruct you how to shape shower floors, etc. This one is strictly to describe the proper recipe for your mix.

A couple of companies also make a mix specifically for shower floors and mud beds. I’ve only used one and it worked quite well. Just follow the mixing instructions on the bag and start with the minimum amount of water they suggest and work up from there.

When set (about 24 hours) the mud bed will be a perfectly suitable substrate for your tile installation. It will be sandy on the top. You can scratch it with your fingernail – stop doing that! It’s normal. I understand it’s counter-intuitive, but it really is normal.

Although you may have been led to believe that creating a shower floor from scratch is a very difficult thing to do, it is not. With careful planning and attention to detail you can create a shower that will last for years without any problems. Getting your mud mix correct is at the core of the proper method.

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JW

I installed my pre-slope yesterday, and it’s been about 17 hours since, and there is some difference in color. Can you look at the image link below and see if you think this is okay and to proceed installing the liner?

http://i109.photobucket.com/albums/n76/stangman16/DSCF2051.jpg

The left side is more hardened and less scratch-able then the right side..

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Roger

Hi JW,

Started on the left, didn’t you? :D It’s completely fine, the left side is just packed a bit better than the right and was possibly mixed with a bit more water. Neither will hurt anything, you’re fine.

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JW

Lol, yes I did – and I was afraid of that, I think it did have a little more water in it.

Thanks!

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Denis

Roger, I just layed the final mud bed for a new shower I am buliding. First time for me. The pre-slope went fine using sand and topping mixed with sand in the CORRECT amount. But I think I screwed the pooch on the final mud bed. I mixed 60lbs. of sand and topping with 50lbs. of sand ! I guess I was brian dead and did not notice that the sand was a 50lb. bag. It has not cured yet but I will check it out after 24hrs. Am I screwed ? You state 5 to 1 is the best ratio but that even 6 to 1 will work. With 60lbs. sand and topping mixed with 50lbs. sand just what ration do I have ? I suck at math.

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Roger

Hi Denis,

You have a 6.3:1 ratio. It should be fine. It may be a bit excessively sandy, but you can skim-coat it with thinset first to lock all that in if you need to.

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Duane

Hi Roger,

First of all, thanks for the descriptive website.

First question: Is “Sand Mix” (Topping and Bedding) the same as “Sand and Topping” mix?

Just want to make sure Im doing this right. I mixed 30lbs (half the 60lb bag) of sand with a 60lb bag of Sand Mix “Topping and Bedding” for the preslope. You said it would be sandy, it is. It just doesnt look and feel like it should. First time building a shower pan so I have only pictures and videos to compare.

Did I mix the wrong stuff?

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Roger

Hi Duane,

As far as I can ascertain the sakrete sand mix is also 3:1. Assuming that, with a 60lb bag there is 15lbs of concrete, 45lbs of sand. To bring your mix to a 5:1 ratio you need to add 30lbs of sand. You have the correct ratio. Why do you say it doesn’t look and feel like it should? You mixed the correct stuff, is it solid?

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Duane

Thanks for the reply. I was reading some other posts where one person described his preslope like the “surface of the moon.” A lot of small craters. Mine is similar. Yes, it is solid. I ended up going over it w/ thinset to fill in the gaps then I sanded the whole thing down. It looked a lot better. Just got done laying the membrane. I feel a lot better now that the membrane is down. Looking forward to finishing the rest. Thanks again for making your knowledge known. I would not have tackled this project if it was not for stumbling upon this website.

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Matt

Hi Floor Elf…

So thank you for all your insight with this site. I actually even got one of your manuals the other day. I am about to build my first shower pan and feel pretty confident after reading what you have here. The only question I have came when getting the deck mud supplies at HD. They actually had a couple different types of sand… Fine, Medium and maybe even another, can’t remember off the top of my head. Any way I know it might be nit picky but I noticed you did not specify and so I am curious if it matters or what you typically use?? Thanks

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Roger

Hi Matt,

I just use the regular mason’s sand. It doesn’t really matter which you use, the finer the sand the easier I find it to work with.

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Scott

Roger,

Another question. Long story short, been tiling the shower walls and protected the floor with a piece of drywall. Decided to check the floor one day and make sure it was doing alright. Started tapping around with my finger and 90% of it had a solid feel. However, there is one area just to the right of the drain, where the sensation isn’t the same as the rest. I don’t want to say it vibrates or makes a hollow noise but I can’t explain in any other way. Are drastic measures in store for me? I don’t want to continue tiling the walls if things need to get torn apart.

Thanks,
Scott

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Roger

Hey Scott,

If you’re using topical waterproofing on the floor then you need to dig out all the loose stuff, put some thinset in there and pack it with deck mud again. If it is just your preslope it will be fine.

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Scott

Roger, the one detail I forgot to leave out…the floor is already tiled. I used a latex thinset modified mortor with a mini versailles design in stone, which comes in 12sq ft sections on a mesh sheet…bought from the tile shop.

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Roger

In that case as long as the tile isn’t moving it’s likely just fine. They will sound different when you tap on them the closer you get to the drain.

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Ken

If I use type s mortar and add sand can this make deck mud ?

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Roger

Hi Ken,

No, because type s mortar has lime in it as well as large aggregate.

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Ken

What about using topping mix , is this the same as sand and top ? Or maybe unmodified thin set mortar as it is just sand and port ?

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Ken

The thin set I have is kerabond , can I use this ? I only have a spot to fill 6″ x 60″ between my kerdi pan and curb , or is topping mix same as sand and top?

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Roger

The kerabond may work if you add 4 parts sand to it. That is simply an educated guess, though. I can’t guarantee that.

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Ken

Thx for your prompt replies bud as I am doing this today ! I don’t want to use Portland as I’m in a small town and it’s an hour away to a big box , what about using rapid set concrete almost to pan top then slope with kerabond and kerdi over ?

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Roger

I would actually add sand to the unmodified, that would be a better option. You don’t really want solid concrete there since it WILL crack. You can add sand to the rapid set, though. That would work.

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Ken

The rapid set is post haste and contains rock , won’t work for dry pack , that’s why I thought pour up to pan then slope with peanut butter unmodified ?

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Ken

Ok mr floor elf one last question what about sikagrout 212 non shink cemititiuos grout , says can be used as a dry pack ?

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Roger

Yup, that would work.

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Roger

If you have any more questions can you PLEASE post them as a reply rather than a new comment? Thanks.

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Roger

Sand and topping mix works, I have no idea what the topping mix is. Is there any reason you don’t want to just use portland cement??? Never tried it with unmodified, never can tell the mix ratios in the different thinsets.

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RUS

Hi Roger,

I did everything you said and my deck mud came out just as you explained.
I’m thinking of putting RedGard waterproofing product and crack prevention membrane on top of the deck mud. Good idea or bad idea?

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Roger

Hi Rus,

You can paint it onto the floor about three inches or so from the walls if you want to. Covering the entire thing, however, may lead to drainage / water retention issues which could lead to mold and all sorts of nasty stuff.

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RUS

Thank you Roger.

I have another issue. I was vacuuming the mud deck to remove and loose dirt from the surface and a small chunk of mud deck came up. how can I patch that area?

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Roger

Put a little bit of thinset in the hole and fill it with more deck mud.

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Kinsley

Hi Roger, I have a hallway that goes from my front door to back door, about 25’long that had slate tile. I tore it up and there is deck mud as the underlay.I planned on tiling over it with the new tile, it is very solid. In fact it was hard to get the tile off. EXCEPT the last 6′ at the back door. This seemed much softer and broke up in several areas to the point that there are several holes that are a couple inches wide and go down to the old wire mesh. Is it ok to patch in these areas with new deck mud?

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Roger

Hi Kinsley,

Yes, you can patch that. I would actually sprinkle some thinset powder into those holes first, mist it with water, then install the deck mud. This will bond the new stuff to the old stuff.

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Kinsley

Hey Roger, thanks a lot.Did as you said last night. Seems to be very solid. Thanks a lot for your help

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John w

I’m going to be using kirdi over dry pack, do I still need to put something next to the plywood or will the kirdi protect the plywood?

John W

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Roger

Hi John,

I have no idea what plywood you’re talking about. I assume the plywood subfloor? If so then yes, you still need to put tar paper or plastic over it first. It is not to protect the plywood, it’s to prevent the plywood from prematurely sucking moisture out of the deck mud before it fully cures, thus weakening it. If you’re talking about some other plywood you’ll need to let me know what that is.

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Jacob

Roger,
Can I use type s mortar for the pre slope and deck mud?

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Roger

Hi Jacob,

No, you can’t. It does not have enough sand in it and will eventually crack.

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Gus

Greetings Roger,

Had a quick question regarding my existing poured pan. I had to rip out the tile the contractor put in – probably one of the sloppiest tile jobs I have every seen – anyways, I wanted to know if it is possibly to cement/ thinset over the existing pan instead of tiling it over again and if so, what you recommend as a sealing method. Would like to retain the natural look of the mud if possible…

Thanks!

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Roger

Hi Gus,

While there are methods to have hydronic concrete as a wear layer (the layer showing and used) it is a very involved and specialized product and installation. Deck mud is definitely not a wear layer, it will not last no matter what you seal it with. Concrete would simply crack unless over 1 1/2″ thick, and may still crack.

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thomas

Roger. Did my first deck mud slope to kerdi drain and will apply kerdi membrane over deck mud. I’m a bit of a perfectionist and there are a few spots that are slightly scalloped. I am concerned that applying the membrane and then forcing out the excess thinset with the edge of tapers knife will make a few waves with the kerdi. If I do a pebble or rock shower basin no worries but I would like it smooth in case I end up with small tile. Is there a way to apply a topping coat to trowel smooth and let dry and then do the kerdi. Or should I not stress and work tile level with thinset on the kerdi.

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Roger

Hi Thomas,

You can float over it with thinset to flatten it, let it cure, then install your kerdi.

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Brandon

Hi roger, I am kicking myself because I did not bring my shower bed cement up close enough to the shower drain lip. (The cement is sitting about 1/4 inch too low) so if I layed tile right now my tile would be sitting below the drain lip and it would not drain properly. I tried a resurfacing cement from quikrete at about 3/8 inch thick, and after a week it started to crack and when I tapped on it it had a hollow sound. I’m willing to do whatever is necessary, but my concern is how strong a thin layer of any kind of cement will be. Please let me know what you think. I will tear it all out if necessary,

thanks,
Brandon

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Roger

Hi Brandon,

You should tear out the quickrete layer, put down a layer of thinset and build up the deck with more deck mud. With the thinset you can go 1/4″ up without problems.

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Jean

For plywood subfloor, you still need tarpaper and lath before putting in bed?

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Roger

Hi Jean,

Yes.

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Bindy

Would you ever do this type of mud packing over the entire bathroom floor? I have a 1920’s home that leans this way and that. The entire bathroom is 5×6.5 feet and from the window wall (where the tub will go) to the bathroom door it slopes downward 1 and 3/8ths of an inch. To match the hallway floor and the toilet flange I can only go up 3/4s of an inch (including tile thickness) so I won’t be able to completely level the floor but I thought I would try to level it out a little. I’m just not sure the best way to do this. I’ve considered just using floor leveling concrete right on top of the 3/4 inch green treated plywood subfloor or alternatively 1/4 inch cement backer board on top of the plywood with floor leveling compound on top of that but maybe packed mud will give me smoother transitions? I plan on using small hexagonal tiles (1920’s style) so they should be able to handle some slope. Any recommendations? Thank you.

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Roger

Hi Bindy,

Absolutely. Mud decks beneath floors have been around over 100 years, and it’s still the BEST substrate to install floor tile over. Same stuff, same methods, just make it flat instead of sloped.

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Dave

Roger,

This is my first shower and maybe I’m trying too big of a project but oh well. Anyway, I’m just wondering if while doing my deck and it ends up taking too long can I do half one day and the rest the next day? Will a cold joint be a problem?

Love your site.

Thanks

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Roger

Hi Dave,

A cold joint could be a problem. There is no reason it should take more than a day. :)

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Scott

Roger,

Thanks for the reply. One more question, is the 4:1 Portland mix generally weak when thin at the drain? Say, where my pre-pitch layer is set? I was careful not yo walk on that later and gently moved a liner over it….when prepping for the final shower pan layer of mud. How would you recommend I fix my spots where the concrete dusted/crumbled upon brushing? Were talking not even a quarter of an inch, or so. Thanks!!

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Roger

Hi Scott,

It is a bit weak on the preslope there before the final slope is done, but it normally doesn’t affect anything negatively. If it’s less than 1/4″ then you should be fine.

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eddieo

No more, liners, no more preslope. One bed, one slope, then kerdi waterproof membrane on top, tile on top of that, done.

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Roger

Hi Eddie,

Yes, I know. :D

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Jess

Having a horrible time doing this .Ive came back after following the instructions as mentioned only to see it was very britaly to the point of any little bit of slight pressure it breaks is that normal ? Did I not add enough water? On a 60lb bag of sand topping quickcrete I added 30 lb of sand and a little more then half a gallon of water , anyways I ebed up talking it out and reworked it I could even bring it back to broken down form with my hands , reworked it added more water not dripping , but wet liked a little better fingures crossed we’ll see what happens

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Roger

Hi Jess,

It’s likely just not packed down wall enough. Remixing it will not work, the cement has already been activated, it likely won’t have enough to resolidify it, but it may.

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Jermey

I am building an shower pan on an concrete floor if i leave the cast iron drain pipe alone and build up from there my deck mud will be about 4″ thick at the drain and about 5-1/2″ thick at the top of the slope. Is this to thick?

Reply

Roger

Hi Jermey,

Nope, it’s fine.

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Scott

Hey there. So here’s my issue. Built up my pre-pan, which admitadely is thin around the drain. The first time pouring the pre-putch layer, a piece ended up popping up near the drain. My second time, things went better off. Is it normal for the mud to be that way? I did mark slightly more then an inch up to get the proper pitch toward the drain. I should also note, I’ve been using the Tile Shop 4:1 Portland cement mixed with only water. Next, after getting the prepitch in, the liner went up and I added to he shower pan level with assistance of the Goof Proof Quick Pitch kit. But due to having to shorten certain sticks on the wall, I mistakingly made each wall go from level at the sides to pitch down to the middle of the wall. Long story short, I added more mud on top, to get the walls level. First off, was that a safe move? I checked that fixed layer and overall 90% is strong and solid…not deteriorating when brushed or with my hand running over it. However, there were four small spots that did dust up and appear as though the mud didn’t adhere. I patched that up again…but should that not work….what are your suggestions? Thank you much!

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Roger

Hi Scott,

The patches should work fine. When using the goof proof shower kit they should be used on the initial (pre) slope, not the top slope. Since they actually slope the floor, and you placed them on top of an already sloped floor, you now have (if done correctly) 1/2″ / foot slope in your shower rather than 1/4″ / foot. The preslope should be sloped and the top slope should actually be a consistent thickness which follows the preslope.

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chiefy

MR. Floor Elf,

My preslope, membrane and deck were all done to your specs. But my deck was pretty sandy after it cured for a couple days. I laid down 2×2 mosaic with peanut butter like thinset. The thinset didn’t “adhere” very well in some spots due to the sandy like surface. It would just roll instead of spreading. I did manage to get an even coat before tileing. Now I’m second guessing weather or not it will bond properly. Any first hand experience or knowledge on my situation?

Reply

Roger

Hi Chiefy,

As the thinset cures it will solidify the deck mud beneath it because it’s adding moisture and the thinset crystals will grow into, and become one with, the deck mud. Very Zen-like. :D It’ll be fine.

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