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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Dear Floor Elf,
My shower pan is somewhat sloped. All I did in demo is hammer-drill out the tile and grout. Can I fix the “potholes” with thinset then lay down the liner and top mud bed? The preslope already exists as I believe the builder used the tar mop to waterproof it twenty years ago. I’d hate to have done double work when it wasn’t necessary. I’m still going to install a liner and new drain so I must use some deck mud no matter what.
If I must construct a pre-slope, I have to make the thinset slurry so the mud will adhere to the substrate. Should I let the slurry dry before I start the preslope? How thick a layer? Is the slurry thin enough to use a paint brush or roller or should it be a little more substantial and use a trowel?
And, thank you for your continued support! (Wasn’t that a Bartles and James ad?)
Susan
Hi Susan,
That was, in fact, a Bartles and James ad. A great tagline, by the way.
Wait, that wasn’t the question…
If you are talking about using the existing pan as your preslope then yes, you can do that provided it is solid enough and in good enough shape to do so. You do not want to fill the potholes with thinset – thinset can usually only be built up to about a 3/4″ thickness. If your potholes are less than that go ahead. The fact that you’ve mentioned the word ‘potholes’ as a descriptor leads me to believe they may be a bit larger than that. If so you can fill them with deck mud. A preslope doesn’t need to be perfect (don’t tell anyone I said that) it only needs to be sloped consistently toward the drain to allow all the water to go where it should. You do want to fill the potholes, though, so water does not get trapped in them. (We call those birdbaths, I guess ours are smaller than yours
) Your entire preslope needs to be aimed consistently downward with no areas sloping back up – gravity doesn’t like that.
If you do make a slurry (info for everyone else) it is simply really thin thinset which is placed on the slab beneath your preslope to adhere the deck mud to the slab. You do not let it dry first, it’s just like installing tile – place your thinset (slurry) then your tile (deck mud), once cured it isn’t going anywhere. You can put it down with a brush or roller but it would be a huge pain – use a trowel. The slurry really shouldn’t be THAT thin, just thin enough to barely hold the ridges when trowelled on.
Thank you for your support!
Hello,
I set the mud last night (almost 24 hours ago) at a 4:1 ratio, and it seems too dry and “dusty”. I guess I expected it to be solid like a concrete pad. Do I need to mist it, let it set further, and check tomorrow, or something else altogether?
Also, it doesn’t seem to be a perfect “dish” shape. For example, it slopes a little horizontally as it slopes to the drain, if that makes sense?
Any advice is greatly appreciated. First time doing this, so you won’t hurt my feelings if you tell me I’ve done this wrong.
Thanks.
- Jon
Ok, well maybe I should have read more before I posted this. I see now that you’ve written that it should be sandy and not to panic. Phew!
Ok, I feel better now. Please feel free to give any other advice if you want.
Thanks.
Hi Jon,
You did it all wrong.
Just kidding…
It’s supposed to be dry. It may be a bit dusty if you did not get all the smaller particles pounded down into the bed enough. If it is a bit too ‘dusty’, so to speak, you can mix up some thinset and coat the top of it to lock in all the small, loose particles. You can try to mist it down with water if you want, it may activate some of the concrete if it did not get enough moisture, but I honestly doubt it would help. I would skim it with thinset and let that cure and that should give you a workable surface for your tile.
For any spots that are not quite the shape or slope they need to be you can either build them up a bit with thinset or you can sand it down with a rubbing stone or piece of sandpaper. Provided they are not huge discrepancies from the ideal slope that will work just fine.
Ha ha, probably! Thanks for the info. I should mention that I have just laid down the first layer of mud. Does that change anything? If not, I’ll go ahead with the membrane and then add the second layer.
Thanks again!
- Jon
Hey Jon,
Makes no difference at all, both layers should be identical in feel and finish.
Hello,
I am attempting to make my own shower in my new house. I have looked at several web sites for advice on how to do it. I think I know how to do the sloped mud beds, but I have a question concerning the curb. My plans are to wrap my curb in green board for tiling. After my first sloped bed is done, I will lay the PVC membrane on from 8″ up the wall to cover the shower floor. What is the best way to secure the liner and green board to the inside vertical curb wall without having to use screws or nails?
Thanks!!
Hey Lonnie,
First, unless you are using Kerdi, greenboard is absolutely NOT an approved substrate for tile in a wet area such as a shower and never, ever for a curb. Even using Kerdi regular drywall should be used rather than greenboard.
To create your curb you should use two or three 2 x 4′s stacked if building on a wooden subfloor, or regular or concrete bricks if over a concrete substrate.
The liner is then wrapped up and over your curb and adhered by bending metal lathe around it carefully (as to not puncture your liner), then covering that with deck mud / fat mud to create your tile substrate.
Greenboard in any part of a shower, especially anywhere below a waterline such as the curb, will do nothing but disintegrate.
Two questions:
1 – Can’t find the sand/topping mix at our local big box store, but we do have a bunch of regular mortar mix left over from another project. Can we use mortor mix and add some sand? If so, how much sand would you guess to a 60 lb. bag of mortar? I tried to find the sand/mortar ratio on the quickrete website, but it’s not there.
2 – how thin do you think one can go with the deck mud? We have a high spot in our concrete floor near the drain – which is just the right height for the level of where our drain height is currently (gives us 1/4″ slope over 1 foot to the drain). Can this work — or should we raise the drain so that our deck mud is not too thin?
Thanks for your help….we really need it!
Hey Russ,
1. Are you talking about regular thinset mortar? If so then no, that won’t work. You can get regular concrete mix or just plain old portland cement and mix it with sand to make your own mix. Mix it at a 5 : 1 ratio (5 sand to one portland).
2. You need to have your deck mud at a minimum of 3/4″ for your pre-slope. You may run into information stating 1 1/4″ but that is for a regular mud pack for a floor. Raise your drain a bit and you’ll be fine.
Regarding question 1 below, actually the leftover mortar we have is a portland cement mix which was used for building our block retaining wall. So, I guess we could use this if I can just figure out the right amount of sand to add to it.
Regarding question 2 below, if the pre-slope under the pan liner is at least 3/4″, does the second deck mud coat over the pan liner also need to be at least 3/4″ at it’s lowest point near the drain?
I hope we are not wearing out our welcome on your site with all these questions…thanks, again.
Yes, you can use that if it is regular portland cement. Just weigh the amount you have left and mix it with 5 times as much sand. i.e. If you have 20lbs. of portland left mix it with 100lbs. of sand.
Yes, your top bed should be 3/4″ as well. It should be 3/4″ thick from the drain to the wall if you already have your pre-slope sloped correctly.
You are absolutely not wearing out your welcome. Glad to help.
both doors are closed
he wont be getting in..
id like it cured harder so that i can apply unmod thinset tomorrow and kerdi it… and hopefully use it on monday/tuesday..
You should be good with that. Just make sure to mix you’re unmod a bit thinner for the Kerdi. It also helps if you use the flat side of the trowel on the pan first just to “burn in” the thinset then trowel it out as normal. Helps ensure absolute coverage and grab.
Have fun!
had to rip it out
.. ripped it all out today morning (sat) and got the 3rd one in… went with a 5:1 mix using sand topping mix + sand… used a magnesium float… helps a lot more i beat it with both a small 4″ cut from a 2×4 and then also with my magnesium float.. also used it to shame it here and there and remove high spots.. i currently have it covered with sheeting so that it stays wet longer.. not sure if thats of any benefit. im in CA., as is on all day s its dry in my house. didnt want it to dry to soon?
Crap – You’re gonna be an expert by the time you’re done.
Covering it will cause it to cure a bit more slowly and make it a bit harder so that will help.
If you have any high spots left after it cures you can use a tile rubbing stone to “sand” it down level – a regular sanding block with coarse paper works as well.
Lock up the cat.
thank you for your response roger
a pic can be seen at
pic of mud
this is after i took a sweeper to it … i started poking around and found a loose spot.. shdnt have done that,,, took a vacum to it and ended up with a tennis ball sized hole
this was one of the spots the cat had messed around.. the other spots held…
i will be using versabond to create a smoothie/milk shake consistency thinset mix.. smear on the tennish ball hole do a 4:1 ish dry pack mix.. and pack it in.. let it dry over night… get my kerdi and unmodified thinset ready and kerdi it up the next day..
if it starts crumbling during the application of unmodified thinset + trowel, ill rip it apart and do again..
p.s. this was the 2nd attempt.. 1st attempt wasnt sloped enough..
Sounds like a good plan! I hope you don’t have to tear it all out (again). From what I can see in the pic your plan should work fine. Good luck.
Hello, how long does it take mud to reach full cure/hardness?
My cat jumped in my 5:1 packed shower bed right after I finished packing it while I was eating and had pulled a decent amount of it apart… I don’t expect it to be usable and will break it apart… I did however pack it again… Just in case… As the mud still had a little hold to it.. Nothing great.. I misted it down with a sprayer and covered it..
I’ll check on it before leaving to work tomorrow and will nit be able to take it appart till Friday… Just trying to prepare myself with how much effort will be required to take it appart agaig
Hi “cat in mud”
Deck mud will be solid in 24 hours and fully cured (for all intents and purposes) in 28 days. Not sure if your cat could do enough damage to warrant removing the entire thing but I can’t see it from here.
The easiest way would be to chip enough out to get a crowbar beneath it and you should be able to pry out reasonably large chunks if you pry from the bottom.
Hello roger –
I just checked it about an hour ago and it is pretty hard already – I will not poke anymore –
thanks for your advice – DAVE
Thanks for the info – I ended up having to use floor leveling cement for the Schluter pan as my floor was a bit out of whack which added almost an inch of thickness to the deck mud. So I used 200 lbs of sand and 40 lbs portland approx – which is at your recommended 5:1 mix – It is curing as I write – how hard does the deck mud get? It seems soft now as in I can poke my finger into it – believe me I packed it tight.
thanks for your advice – have a great day – DAVE
Hey David,
It will be sandy on the top so you can rub it and remove sandy particles – don’t do that either, it’s normal. It should cure to hardness in about 24 hours.
It will get rock hard – literally. Stop poking it with your finger.
Hello – One related question?
I am creating my mud bed with the prefab Schluter 48″ shower pan and then filling in the uncovered areas with deck mud – overall the sq footage is 6 sq feet. How can I calculate how much deck mud – ie portland and sand – I need to fill the gaps – the schluter pan is 1.5″ thick.
Thanks in advance for any help – DAVE
Hi David,
To determine how much sand to use per square foot (average) I use 10 lbs. sand and topping mix and 5 lbs. sand per square foot. So for your six square feet 60 lbs. sand and topping mix and 30 lbs. of sand should get you pretty close.
Thanks for all your help.
I put the vacuum to it, pulled up the easily loose stuff… I guess its just a few little patchs here and there.. and seems pretty secure everywhere now. There is about 5 tennis ball sized areas that are now about 1/4 down. I just add a bit extra thinset to fill those, So I will go ahead on put my tile down on it. Thanks again.
Most of its sandy….. which I assume is fine. Its the edges where I used a 2×4 to make sure they where level… I thought I had that as my best pack
It will rub away… if I rub my finger back and forth aggressively, I can remove a 1/4 in 30 seconds.
Someone else recommended using a wet vac to remove the loose parts… and then finishing it off with some FAT mud, that has an latex acrylic add in it. You think that sounds right? The voids seem small for thinset and mud.
Thanks!
Sandy is fine. It’s supposed to be like that. Stop doing that.
You’re gonna hurt your finger. If you continue to rub something against it aggressively enough (even your finger) you will be able to rub it all the way to the floor. It is not like concrete – it isn’t supposed to be.
If you’ve rubbed enough to cause an area that needs filled you can do it up to 1/4″ with just thinset. You do not need fat mud – which is just drypack with more water and lime to make it sticky – it’s for vertical surfaces such as walls.
It sounds to me as if you’ve correctly fabricated your shower floor. Stop questioning yourself, it’s fine. There is a reason I included the second to last paragraph in the post above.
And stop rubbing it!
I did an install with 4:1 mixure, and I notice that some of the surface, mainly near the walls, seem to crumble really easily, most of the base does not. Should I try to remove the loose parts and refill this with an adhesive in the mixture? It seems to me I might have made it too dry here.
Hey HR,
A 4:1 mixture is fine for your drypack. The surface is supposed to be sandy but should hold together. If by “crumble easily” you mean it’s sandy then it’s fine.
If you mean you can pull chunks at a time up or it’s cracking that means you did not pack it down well enough. It is not a sign that it was not wet enough.
If the latter is the case you can pull out whatever chunks want to come up and pack more deck mud into the space. You want to first put thinset into the void to lock the old and new parts together. Then make sure you pack it down WELL. Do not use adhesive in the mixture.
If the surface is simply sandy – that’s normal. You can go over it with thinset and the flat side of your trowel before you tile to make tile installation a bit easier.