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.

Previous post:

Next post:

John

I mixed the topping and sand as you subscribed. It has been set now for about 18 hours. The mortar bed looks good, but as you mentioned it will scratch, which makes me a little nervous.

My question is about the curb. I used the same deck mud mix to build the curb (the sub structure of the curb is 2 2X4 stacked on top of each other with a ¾ “ plywood spacer in the middle to bring the sub structure of the curb height to 3 ¾” above the plywood floor and covered in metal lath). I am concerned that the deck mud mix I applied to the curb is strong enough (concerned about crumbling). Should I have used a different mix to cover the curb in mortar? If so, I can redo, just wanted to check with you. THANK YOU!!!

Reply

Roger

Hi John,

Ideally you would use wet mud, rather than deck mud, on the curb. But your curb will be fine once you get it tiled. It is plenty strong and stable enough. Don’t let the deck mud make you nervous. :D

Reply

pete

Mr. Elf
what is the thinnest the dry pack should be applied

Reply

Roger

Hi Pete,

Absolute thinnest is 3/4″. You can go thinner than that at the drain on the preslope.

Reply

Kevin

Roger,
How much mix (amount and volume of bags) do I need to cover 32sq feet 1½-1¾″ thick?

Thanks.

Reply

Roger

Hi Kevin,

16 bags of s&t mix and 8 bags of sand. 80lbs. and 50lbs. respectively.

Reply

Ken

Before installing my membrane and deck mud should my sub floor be at least a 1 1/2″ . Double 3/4″ plywood

Reply

Roger

Hi Ken,

Ideal, but not completely necessary. 1 layer of 3/4 is fine.

Reply

Steve

When installing the deck mud over a concrete subfloor, is there any prep that needs to be done to the concrete before putting the deck mud down (other than cleaning it)? One guy’s opinion was to put a thin layer of modified thinset down first and then install the deck mud over it (before the thinset layer dries).

Reply

Roger

Hi Steve,

Yes, you should put thinset down over the concrete to bond the bed to the concrete.

Reply

Steve

Thanks, Roger…

You’re the man!

Reply

Karl

Roger,
How much mix do I need to cover 47sq feet .75″ thick?

Reply

Roger

Hi Karl,

8 bags of sand and topping mix, 4 bags of sand.

Reply

Garth

Roger, quick math check. 80lb bags of sand and topping would need 40lbs sand? Sorry my local building supply only had 80 pounders. What is typical coverage say an 1″ thick per 60/30lb mix? Or better yet 80/40lb lol

Reply

Chris

Quick question, when you say “sand” is that the same as “quickcrete sand/topping mix”?

Reply

Chris

lol nevermind, I re-read and you already mentioned the sand/topping mix

Reply

Craig

When making preslope mud would it better if it is a little on the drier side or wet side or is there a large enough variance that it wont matter…

Reply

Roger

Hi Craig,

Doesn’t matter at all.

Reply

phil

Hello,

Finally had the courage to lay my mudbed. I will lay down the kerdi tomorrow morning. I think I mixed the mud on the dry side. It’s quite sandy. Is their any trick to lay down the ditra-set for the kerdi. I have a feeling the sandy top might cause some problems. Should I mist it first or make the thinset extra watery. Thanks

Reply

Roger

Hi Phil,

Although I’m certain I’m way too late, you can skim coat the surface with thinset first, let that cure, then install the membrane.

Reply

Wendy

We were nervous about doing the shower pan ourselves (didn’t see your site in time) and hired a plumber. We had planned to wait a couple of weeks before tiling as we were leaving on vacation and he agreed this was not a problem. Now we are back and ready to begin tiling the shower floor and walls, but the shower pan is cracked. Plumber now says we should have tiled the floor the next day. However, if the pan cracked before we started work, wouldn’t it crack even after the tile was laid? We’re not sure now whether to have the plumber come back and redo the pan, try it ourselves or hire someone else. I also do not have any wall board up yet or wall tile and noticed this was completed down to the pan liner in most videos we watched before the floor tile was laid. What is the rule on when this is put up?

Thanks for your help!

Reply

Roger

Hi Wendy,

It depends on how the floor was built. Is there a proper preslope? Is there a liner? Are there two layers of deck mud with the liner between? Did he use actual deck mud to build your floor? (Cracking is indicative of an improper mix). There are way too many variables and unknowns for me to give you a recommendations on how to proceed. It may be fine, it may not – I can’t see it from here. :D I’d need a lot more info to be able to help.

Reply

Bri

How do you mix the mortar that sits around a 3-piece clamping drain (i.e. Nobleseal) and on top of the pea gravel (or whatever you choose for weep hole protection)? If it’s too dry couldn’t it crumble down through the gravel and clog up the holes? If it’s too wet will it be strong enough, or possibly shrink/crack? Thanks!

Reply

Roger

Hi Bri,

You don’t mix mortar for anywhere around the drain. If you’re talking about deck mud – the same way you mix it for everything else. It will not crumble down through the gravel and clog up the holes. And it would have to be extremely wet to shrink and crack significantly.

Reply

Eye

Can I use the same deck mud from my floor to do my bench seat as well?

Reply

Roger

Hi Eye,

Aye.

Reply

Crystal

Hi! We made the mud bed, and let it cure 24 hrs. My husband took the shop vac to clean up the sandy top. It was scratching out, and he got a little vigorous…..we now have some craters. Can this be patched, or do we need to tear it out and start again?

Reply

Roger

Hi Crystal,

It can be patched with thinset (smaller) or thinset and more deck mud (larger holes).

Reply

Pete

Hello Mr. Elf,
Advisable or even recommended to coat the floor after dry packing with Red Guard?

Reply

Roger

Hi Pete,

Not if you have a pvc or cpe membrane under it. You want one or the other, never both.

Reply

Bev

Humm we had to use a bit of dry pack to fill in around a Kerdi shower pan. We were told to mix it 1:1 sand, cement. The fill space is about 1″ around 3 sides and about 6″ wide across the front of the shower. (60″x40″ shower floor)
We have already covered it all with the Kerdi fabric and are currently doing the water test before we start tiling the floor.
Is this 1:1 mix going to cause problems down the road??

Reply

Roger

Hi Bev,

Maybe. It depends on a LOT of factors. My guess is that the 1″ fills around the sides won’t be a problem at all, but the 6″ across the front may be. Is your substrate wood or concrete?

Reply

Bev

Concrete. The dry pack is about 1.5″ thick. The thickness of the Kerdi pan.

Reply

Bev

Also, on this 60’x36″ shower floor, I planned to frame it with about 6″x24″ strips of the (12×24″) porcelain floor tile. Cutting a diagonal seams at the corners to allow for these long tile pieces to follow the pans slope, then filling in the center with small mosaics.
Might this work, or should I just do the entire pan in mosaics??
Thanks so much. Bev

Reply

Roger

You should be fine with the border.

Reply

John

Quikrete says the sand/ topping mix alone is used for preslope and top and that nothing needs to be mixed. Can you do it that way or are you asking for trouble?
They also say it does well as the curb

Reply

Roger

Hi John,

I’m sure they’ll say anything that will sell their product. :D Deck mud needs to be a minimum of a 4:1 mix. The extra sand in it allows for movement compensation and prevents that from causing cracking in your tile installation. The extra sand needs to be in there. It will work for a curb – if you take half a day to shape it and try to get it to bond to a vertical surface. Wet mud is sticky, it does this. Deck mud is not.

Reply

Matt

Starting my first tile shower project. My question is this…I’m making a mortar pan first, thin a membrane, then a mortar pan again that the tile will lay on. Is the initial pan (on the plywood subfloor) the same make up as the mortar pan that will go on top of the membrane (the pan the actual tile will be on)?

Reply

Roger

Hi Matt,

Yes, your preslope is made of regular deck mud as well.

Reply

Leave a Comment

;) :wtf: :wink: :whistle: :twisted: :suspect: :shades: :roll: :rockon: :oops: :lol: :lol2: :lol1: :idea: :guedo: :evilb: :evil: :eek: :dance: :cry: :corn: :cool: :censored: :bonk: :arrow: :D :?: :-| :-o :-P :-D :-? :) :( :!: 8)