Problems with dry pack shower floor [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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Brian blackburn
07-14-2014, 09:10 PM
I am remodeling a bathroom and building a new 4'x8' shower. Existing floor is concrete slab. I followed all the instructions on this website to make dry pack mortar and installed the pre slope yesterday. I mixed 60 lb bags of Sand Topping Mix and added 25 lbs of play sand to get a sand to cement mixture of close to 5:1. I dry mixed this thoroughly, then added water slowly to get the consistency described in the dry pack article. I added 6 cups of water, and I got the mixture to pack and hold its shape perfectly, just like the pictures on this web site. My hand was clean, and the mixture crumbled easily, again just like the pictures. I dry missed the mixture, and mixed it with water, in a large flat-bottom wooden trough, using a mortar hoe, so I know I got it thoroughly mixed.

I used the pre-pitch sticks to get the slope of the floor correct. With the dry pack mixture, I was able to fill in the sections of the floor between the plastic sloped sticks and screed it cleanly to the top of the sticks. I packed it down with a trowel and a 2x4 end, and I added mix, packed, and screeded until everything was packed and flush with the top of the sticks.

The whole floor took 4 bags of sand topping, 2 -50 lb bags of play sand, and it took about 3 hours to complete the whole floor. I did it in 4 sections, so it took about 30-45 minutes to work each section after I mixed the material. By the time I finished with each fourth of the floor, the mix was starting to get a bit dry, but it still packed with a trowel and leveled out very nicely.

I was really impressed with the instructions on this site. I have used concrete and mortar before, but never dry pack, and without the instructions on this site, I definitely would have added much more water than I did. It behaved and screeded out exactly like the instructions said it would. When I was finished, I was amazed at how nicely the whole area looks perfectly smooth and sloped. I really thought I had an absolutely perfect first layer for my shower floor.

I deviated from the instructions on this site and followed the instructions in videos for the pre-pitch and quick-pitch tools. They said that when the packing and screeding is finished, I should use a sponge to gently add water to the whole floor, to make the mixture a little wetter. I used an 8-oz spray bottle to gently mist the whole floor, to add a little more water to the mix. I probably added about 8 or 10 8-oz bottles of water to the floor, misting it over the whole area. The mix darkened in color, but there was never any obvious free water anywhere on the floor. I let it dry overnight.

Today, 24 hours later, the floor is very dusty on top. There are places where it acts like it never got wet at all. There is loose sand and cement dust all over it. There are places where the pack is very loose and I can use a finger tip and dig half an inch or more down into loose pack material. There are places where the floor feels very solid, and other places where it sounds hollow when I tap on it. What happened? I fear the whole floor has to be torn out and redone, but I followed the instructions exactly and it appeared that everything worked perfectly. At this point, if I redo it, I don't know what to do differently. Help please?

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07-14-2014, 09:52 PM
Hi Brian. :)

There's often a little sand left on top when you're done. Vac up the loose stuff & let us know what's left. Worst case is a re-do, and this, then, becomes "practice". No big deal there, sand and cement are cheap. Post a few photos too so's we know what you're lookin at. :)

07-14-2014, 10:07 PM
I probably wouldn't have added the extra water at the end. You run the risk of washing the portland off the sand, which may be why it's so crumbly now.

Three hours seems like a long time to finish, even for a novice and that size of a floor.

Also, from your description, it sounds like you screeded the mud, then packed it down. Should be the opposite. Pack it down til it's a little above the sticks, then screed it flush. Once it's packed down, you shouldn't be adding any mud. If it's too low after packing it down, dig out that area that's low and repack it. Then screed it off.

Steve in Denver
07-14-2014, 10:49 PM
For comparison sake, I recently did my first dry pack shower base (about 4' x 3-1/2') and it took every bit of 1-1/2 hours. I bet I could do it in half the time now, but first run through you don't know what hell you are doing, so you compensate by going slowly. I did mine in two batches.

07-15-2014, 08:23 AM
I added 6 cups of water....

6 cups of water to 60 lb bags of Sand Topping Mix and added 25 lbs of play sand????? I ain't no pro, but my guess is that the mix was way too dry to start with. I know I used much more water than that in my mix.

Brian blackburn
07-15-2014, 10:38 AM
Yes, I thought 6 cups of water seemed like way too little, but everything on this site that talked about dry pack stressed to go easy on the water. With 6 cups, the mix behaved exactly like the pictures and text that described how it is supposed to clump and hold its shape, but not have any excess water showing.

Anyway, I think I may understand what I did wrong. I used a shovel to fill in between the sticks, loosely spread it around and screeded it off to get about the right amount in each section, then packed it down. At that point, it was lower than the top of the sticks, so I filled in more material and packed and screeded again. By the time I was finished, there were spots that were maybe 1/8" low, so I added a little mix to them and packed that down before final screeding. I think the thin final patches I added didn't blend well with the material I had already packed, and that is why there are loose spots.

Some of the floor feels very solid, exactly like I expected. Other parts are loose and crumbly. I am going to sweep and vacuum away the loose stuff and see how much is left. I thought I would also pick away and dig out at the parts that seem hollow. When I am finished, I suspect I will have parts of the floor that are completely full and solid, and other parts where there will be holes that might be 1/4" or 1/2" deep. If this is the case, will I be able to mix more wet material and fill in the holes, or do I have to tear out the whole floor and redo it? This is the first layer of pre-sloped floor which will be under the rubber liner and another 1-1/2" of cement floor.


07-15-2014, 10:52 AM
Will let the pro's chime in on this one, but technically the only reason for the pre-slope is to pitch the pvc liner towards the drain. The top mud bed is the important layer. I believe you should be ok with patching the pre-slope layer.

07-15-2014, 12:56 PM
I agree Bill,

I purposely made my Pre-Slope wetter "not slumping" or "pouring"so I could be sure to have a solid smooth base for the liner.I used a 4:1 Deck Mud mix with no added sand.I still packed it in but made sure all the sand was coated well with the Portland & water in the mix.

It's easy to have dry pockets of material that don't get mixed well enough when doing a dry pack.

For the final mud deck I will be adding sand to the mix and using less water.

Brian blackburn
07-15-2014, 05:39 PM
I inspected the floor closely this evening, after 48 hours of drying. Some of the holes shown in the attached pictures I dub all the way to the slab with my bare finger. The pack just crumbled. In other places, it is a little stronger, but a few seconds with a putty knife and it completely came apart. Other places feel very hard, like the slab. Still other places feel firm, but if I tap on them with a putty knife, they sound hollow.

3 pictures should be attached. the first shows the complete floor immediately after I finished filling and packing. The second and third pictures show some of the places that crumble.

Can I patch these bad spots and move ahead with the liner and the rest of the floor? I am afraid I probably should tear out the whole thing and redo it.

07-15-2014, 06:06 PM
Brian, you can get away with a lot of filling and patching and such in a pre-slope. All that's required there is an adequate slope and a flat surface solid enough to support your shower floor. There is no tile industry standard for the pre-slope construction on accounta it's no part of a tile installation. It's plumbing.

The final mud bed, on the other hand, needs to done properly in one placement with correctly mixed deck mud well packed and shaped and cured. That one hasta be right as it's your actual tiling substrate as well as part of the water removal system.

I strongly recommend you dispense with those plastic strips in the final mud bed installation.

My opinion; worth price charged.

Brian blackburn
07-15-2014, 06:33 PM
CX - thanks for the advice.

Curious - why do you recommend doing away with the sloped sticks? Since the shower is 8' long, I don't think I have the skill to fill and trowel the whole floor to a uniform slope. For the first floor, I thought the sticks worked perfectly. I was able to screen and float exactly flush with the top of the sticks and I got a very smooth and flat floor with uniform slope. I obviously had problems, but I don't think the sticks caused my problems.

Thanks again,

07-15-2014, 06:50 PM
Again, in the pre-slope they likely make no difference and having well defined lines in your mud for the cracking to follow doesn't make much difference when you're fixin' to install a 40 mil thick cleavage membrane and another 1 1/2" thick (minimum ANSI requirement) mud bed on top of it. In my final mud bed, though, I'd just as soon not have that "feature."

My opinion; worth price charged.

07-15-2014, 08:08 PM
I agree, if there's any movement and cracking, it will be along those sticks.

If you want to, skim coat the preslope with thinset and let it dry. I also would get a clean damp sponge and clean the drain. That circle groove should be free of sand and cement.

Tiger Mountain Tile Inc
07-15-2014, 10:11 PM
I'm going to provide a bit of a counter argument to what Davy and cx mentioned but please keep in mind that there is a wealth of experience speaking in posts 12 & 13.

For many DIY'ers, I don't think the mudwork part of our trade comes easily. If it's something that you struggle with and you are unwilling to hire it out to a professional then I think a properly sloped pan is preferrable to one that doesn't slope right- even if it requires having sticks embedded in it.

This is my opinion and you'll have to make your own decisions taking this and the last two posts into account along with your own abilities. :)

Tiger Mountain Tile Inc
07-15-2014, 10:12 PM
Also, I just wanted to add that the drain looks like it domes up- or is higher that it should be. You want that preslope to drain and the drain can't be too high. :)

edit: What's the plan for the one end with the pipe protruding into the pan?

Brian blackburn
07-16-2014, 05:44 AM
Good comments and questions. You guys are really able to spot a lot of detail in a few lousy pictures.

The pipe in the floor at the far end of the shower is where the drain for the bathtub used to be. I trenched the floor with concrete saw and jackhammer to move the drain to the center of the shower. Then I had a vent problem, which I fixed with the pipe shown. Long story, but I am confident I have that part right. As far as the pipe exposed in the shower floor, I believe it will be fully covered by the top layer of mud, and if it isn't, there is going to be a concrete and tiled bench across that end of the shower. If any pipe is still exposed, I will notch the back of the concrete blocks as I build the bench, and then it will be completely covered.

When I installed the drain and flange and filled in the trench with concrete, the drain flange wasn't perfectly level. I had to raise the drain a hair to level it. When I did that and poured the concrete and let it set, the flange is about 1/2" too high above the rest of the floor. So when I installed the sloped sticks, I cut a bunch of little scraps of 1/2" plywood to put under the sticks. Every stick is supported on about 5-10 scraps of plywood. I glued the scraps to the floor, then glued the sticks to the scraps. That produced a perfect uniform slope all the way to the lip of the drain flange. The scraps of wood don't go right up to the edge of the flange, so about 6-8" of each stick closest to the flange is unsupported. I cut off the ends of the sticks closest to the flange so they wouldn't be in the way as I floated the floor around the flange. That's why you don't see sticks close to the flange in the pictures. But despite all the other problems, I am confident the floor has a uniform slope down to the flange. It doesn't hump up close to the flange.

Based on advice on this post, I was going to try to patch the bad spots in the prefloor and move on with the liner and main floor. I went in last night with a soft bristle brush to sweep up the broken-out parts, and as I kept sweeping, floor kept coming up. I am sure I used too little water, and parts of the floor are just dust. I have now decided to tear up the whole prefloor and start over.

I will mix it just a little wetter this time, work faster, and pack it better before screeding.

Any other advice so I can get better results the second time? I have also read about putting thinset down on the concrete slab before adding the mud. I didn't do that the first time. Is that recommended? What does that accomplish?

Thanks very much,

07-16-2014, 05:59 AM
posted by Brian:
Any other advice so I can get better results the second time? I have also read about putting thinset down on the concrete slab before adding the mud. I didn't do that the first time. Is that recommended? What does that accomplish?

Helps for the mud to bond to the concrete slab. When I go over plywood I put down tar paper and diamond lathe. This anchors the mud to the floor, same concept different substrate. If you didn't do that the first time if will make it easier to remove it cleanly:)

Brian blackburn
07-18-2014, 12:21 PM
What is the difference between modified and unmodified thinset?

I have at least 3 places I think I need to use thinset:
1. Spread over concrete slab before laying down mud for shower pan pre-slope layer.
2. With fiberglass mesh tape to seal seams and joints in hardibacker board underlayment.
3. To install porcelain floor and wall tile.

Which do I use for these tasks - modified or unmodified thinset?


MAPEI - Technical Service
07-18-2014, 12:35 PM
Unmodified thinset does not include polymers. Modified thinset includes polymers designed to give the thinset better 'grab' to both the substrate and the tile and flex slightly instead of crumbling. The 'grab' is very important when using porcelain tile that does not have much porosity. For all of the applications mentioned I would recommend a modified thinset if porcelain tile is the product being applied. Our Ultraflex 2 is a good example of a quality, modified-thinset mortar:

07-18-2014, 02:15 PM
Brian, please keep all question related to this project on this thread. That way anyone who wants to answer questions has the history in one place.

It's important to match the thinset to the product you're using. Check the manufacturer's recommendations for the proper thinset application. For instance, Schluter Kerdi and USG Durock membrane are similar products that function the same way, but one requires unmodified and the other requires modified.

For some cement backers, you can use the cheapest thinset you can find between the subfloor and backer. But Hardi requires a modified thinset for that application. Not sure why, but they do.

Brian blackburn
07-18-2014, 02:36 PM
Excellent. Thank you Dan and Kevin.

Brian blackburn
07-22-2014, 11:17 AM
So often these days, the problem is too much information, not too little.

Two questions about cement backer board:

I read a few books, some on-line articles, and some forum posts, and I had in my mind that the general procedure is as follows:

Pre-slope floor
Backer boards, over top of liner (with a little gap at the floor)
Final mud floor layer, such that mud covers the bottom inch or more of the backer boards.

Then I saw some articles and video that said this was an absoloute no-no - the final layer of mud should not touch the backer boards.

Then I realized that I think this advice applied specifically to GP DensShield.

I am using 1/2" Hardie Backer Boards for the walls to be tiled.

Do I run the backer boards down to the liner and have the final layer of mud cover the bottom of the boards?

Second question:
I read a lot about the importance of having all the studs flat and in-line before installing the backer, which I understand. I did this the best I can, planing down a few studs in places, and adding sister studs in a couple more places. I have all the backer boards installed except the bottom row, which I won't do until at least the first layer of mud floor is finished (depending on the answer to my first question above). The backer boards all look very good and smooth - no hills or valleys at all. I think they are in good shape.

I have purchased Hydro Barrier to seal the corners and niches and to waterproof the backer board. The instructions for the Hydro Barrier say to first seal all backer board joints and corners with thinset and mesh tape, and then to put a layer of Hydro Barrier over them, imbed their fiberglass anti fracture membrane tape, and cover with another layer of HB. Lastly, the instructions say to paint the entire surface of backer boards with the HB.

How much thickness will build up on the joints when I use thinset and tape, then HB and tape? Is this enough thickness to cause problems when setting tile? How much deviation in the backer board surface can be absorbed by thinset when setting tile?

Richard Tunison
07-22-2014, 12:12 PM
James Hardie does not want his boards embedded in mud either. Just use regular cement board so you can embed the board as it's the only thing that secures the bottom of the boards.

Build-up is a problem with small tile and a small notch trowel. What size are your tiles?

Richard Tunison
07-22-2014, 12:23 PM
Don't forget to notch your studs and set the blocking back (or shim out the walls) to get over the liner and it's associated folds and dam corners.

A few diagrams for your viewing pleasure. Please note the dam corner and liner is not in a notch in this photo as those walls were floated with mud and did not require that treatment.

Brian blackburn
07-22-2014, 02:17 PM
I think the tile will be 12 x 12, or maybe some 12 x 24.

What is "regular cement board?" Just like everything else, I can find all kinds of conflicting information in books and on-line. Some say it is ok to bury the hardie backer in floor mud, with a properly sloped floor and liner. Other sources say never to bury the board.

I have already installed all the Hardie backer all around the 4' by 8' shower, except for the bottom row. If it is ok to bury a different type of cement board in the floor mud, I could use the different board for the bottom layer.

If I use a pre-sloped floor, liner, and top layer of mud, would it be appropriate to also seal surface of the top mud layer with Redguard or Hydro Barrier?

07-22-2014, 02:26 PM
Duroc can be, and is recommended to be, buried in the top mud bed. I believe Wonderboard can also be buried.

As far as too much information...... I suggest you pretty much stick to the information provided here and disregard all the you tube videos and such. I'm sure you've seen some of the post on here about bad tile jobs from hired "pro's".

Richard Tunison
07-22-2014, 03:10 PM
Truth be known, some folks have no problem with embedding Hardie in the mud, including me. If you have it already, I'd use it.

Nothing on top of the final mud bed. That would negate the primary purpose of deck mud (very porous) to get water to the liner and the weep holes over your beautifully sloped, pre-slope. :postitbg:

Jim Cordes
07-22-2014, 05:40 PM
The deck mud had a bit too much sand, play sand is not good for mud work, Also once you pack it down you don't want to add more unless you rough it up agian. but it is only a pre-slope..dress it up with some thin-set making sure you don't have spots that wont drain..and dont worry too much about it.

the plastic screed strips can't be used on the final bed because you all ready have proper use them again will be too much pitch, the second layer should be uniform though out to maintain the proper 1/4 ft. drop.

I don't embed into the mud unless I am applying a bonded waterproof membrane to the surface..since you have a traditional shower you won't be using a surface membrane.
embedding promotes wicking...also be wary of a cbu that contains organic materials as it can promote mold growth..

07-23-2014, 01:20 PM
I just finished my 3rd attempt at a pre-slope which finally seems usable so I thought results from my experimenting might be helpful as I've had the same issues with sandy/crumbly surface.

1) a slightly richer mix of 4.5:1 (by volume) seems to be easier to work.
2) the ratio for water for a standard 5:1 dry mix is about 10(S):2(C):1(W)
3) given 1) and 2), the stability of the end result (slightly sandy but not crumbly) is mostly a direct result of a) time and b) pressure. The descriptions of " have about 30-45 min..." and "...really pound the mix..." are dramatic understatements. The mix needs to be dry but that also means it is drying out very quickly so a) MUST be worked very fast (which is very hard when you're learning) and b) must be compacted really well (which means laying the whole floor with a 2x4 as you can't apply enough pressure with a trowel (well, maybe the pros can...). I found it necessary to really continuously pound (and hard) the mud with the edge of an 8-in 2x4. (When near the final slope surface I switch to pounding the the 2x4 flat. It's a cycle: pound, screed, pound, add, pound, screed, pound... I only use a small trowel to spread mud.)
4) do a dry pre-mix of all the mud and then separate into buckets where you know how much water goes with each. The pros can serve it up wet all at once but I can't -- but fast wet-mixing in small batches is easier for me as long as I've pounded and screed-ed the installed batch close to perfect. Again, I had to learn to work furiously at this and I was still too slow.
5) Any remaining mud at the 'leading edge' of the work (which is drying out) I toss as I can't pound it well enough to bond.
6) By whacking/packing really well (and at a thickness that is too high) the screed removes the excess leaving only a thin bit loose (which is then re-packed with the 2x4 flat) -- whereas having to add fresh mix to packed mix requires a lot of extra pounding to get it to 'bond' (so use the freshest mud available from the mix).

As stated, IMHO ... Just thought a beginner's experiences might help explain what other beginner's have experienced.

07-23-2014, 06:16 PM
Dave, it's really not at all necessary to try to beat the mud into submission. It simply needs to be firmly packed before you carve it into shape.

I do all the packing on a shower floor with a magnesium or wood float, usually just whichever I have in my hand at the time. The effort needn't be brutal at all, just firm.

My opinion; worth price charged.

07-23-2014, 06:33 PM
CX, I'm sure that works -- except it didn't for me the last time around -- and I suspect that my 'technique' was lacking. I used a wood float and tried to 'work it' into a pack but when cured, a lot of the pre-pan was soft enough to fall appart with a paint brush (while brushing the sand off the top). This time, I applied a lot more effort (still lacking technique I'm sure) and got much better results. If I were learning the trade, not just remodeling a bath, I'd likely learn how to do it with a float. That's why I was guessing that the guy who started this thread, might have had a similar experience. Thanks and cheers.

Jim Cordes
07-23-2014, 06:55 PM
pound, screed, pound, add, pound, screed, pound

The "add" should be at the front of this list not the middle. Once you pound then you cannot add more unless you dig it back up and start over.

Add the mixture evenly and higher then you plan to go..once packed down you should still be higher,then screed that off, again avoid adding after you pack.

You should not have to turn a 2x4 on edge or have problem with drying out.

4.1, 5.1,6.1,3.1 it really does not matter much it should still work, as long as you dry mix it together first making sure that all the cement particles are touching sand particles, I shoot for about 4 or so to 1 myself. Too much cement it gets lumpy and hard to work(and tear up your hands as well), too little you run the risk of having sand spots that didn't have any cement to hold them together. If you avoid those two things you should be fine.

Use good sharp sand( biggest you can get that that does not have rocks or pebbles in it.) Big sand will only pack down so much then kinda stop solidly. small sand or play sand will just keep sinking the more you pack it down.This is really important when you dont use pre-made DIY screeds since you would be making rails out of mud to guide of off and you want then to be solid.

Also don't play with it too much or the surface will be then normal.

Steel trowel or even magnesium for final pass will bring the cream up and make the surface harder. If in a sloped shower I sometimes use my steel pool float so as to not dig into the mud. But remember there is nothing wrong with skim coating it with thinset after it dries to touch it up and get a harder surface if need be till you get the hang of it.

Truth be told it does not have to be pretty to work well, as much as we strive for perfecting the "art of mud". After you do a few hundred of them you kinda quit worrying if it has a divot of two in it that will be filled with thinset anyways. Has to be level on edges,have good slope and be solid that really all that matters

07-24-2014, 01:17 AM
Jim, Thanks for the insight. I've read a lot of web comments on the topic and yours is the first one I can recall to address the detail of getting a packed, 'thick enough to screed' layer in one shot -- that and your note about using coarse sand.

As 'advertised' in many web comments, I used 'play sand' from HD and found its uniformity easy to work and mix -- though I'll admit it has been hard to pack uniformly. HD also has bagged 'all purpose' sand for outside use but word says it contains small aggregate which I'd thought would be hard to work and get a good surface (like using concrete mix + sand).

I think my 3rd pre-slope will cure good enough to use, but now it sounds like I should shift to the outdoor sand for the top pan layer. I gave up on the 'pitch sticks' product (terrible) for the pre-slope so will stick with my multi-length drain-to-edge screed sticks on thick-pack mud then trowel. Bonding tile to a sandy surface seems like a bad idea.

07-24-2014, 08:33 AM
I'm still sticking to my original thought about the OP's 'mud' was way too dry to begin with. There is no way in hell 6 cups of water mixed with 60 lbs of topping mix and 25 lbs of sand was wet enough to do anything. I use almost that much liquid when mixing my thinset. Also, I'm having a really hard time figuring out why so many people have problems with deck mud. It ain't that hard to work with.... :stick:

Truth be told it does not have to be pretty to work well, as much as we strive for perfecting the "art of mud". After you do a few hundred of them you kinda quit worrying if it has a divot of two in it that will be filled with thinset anyways. Has to be level on edges,have good slope and be solid that really all that matters

This is a very good statement.

Jim Cordes
07-24-2014, 08:01 PM
Well the thing is every box store I have went to does not carry good sand..maybe your is different who knows.

I get mine at the brick yard, alot cheaper too..a buck a bucket , they also have silica sand that I have found works pretty good..might want to try that.

A little sand on the surface wont hurt anything..the thinset will suck it right up and make it part of the thinset, you can always skim it with thinset before hand if you want though.

good point Bill

07-24-2014, 08:11 PM
In a pinch, I've used the all purpose sand from Home Depot and it seemed to work fine. It has some small grits of sand but also has some larger grits too, up to about 1/8 best I remember.

Jim Cordes
07-24-2014, 08:17 PM
I suspect they have different sand for different parts of the country, even if it has the same label it doesn't mean that the company that packages it doesn't have different local suppliers.

I mean I doubt they are going to spend the money to transport sand across the country. I sure wouldn't

07-24-2014, 10:50 PM
Now that my 3rd pre-pan attempt has cured, it's much much better though I will thinset-seal the surface. I do have a bit of sand and a few small softer spots (clearly less-well packed) but will be ok.

I do believe that, with experience, it would get easier but still easily recognize the lack of a good recipe -- for both the ingredients and the procedure -- for the first-timer. While there may not be a need for hard rules, some insight as to both good rules about the details, AND the why they exist can go a long way toward getting it right the first, or at least second, time.

Thought: 60 lbs topping mix (3:1) + 25 lbs sand ~= 70 lbs sand. At ~100 lbs/CF, this is about 0.7CF sand. At 5:1 ratio, (and using my own guess of 1/2-part water for 1 part sand), that mix would need ~0.07CF water which is about 8-1/2 cups if I did my estimates right. So, 6 cups only sounds a little dry IMHO.

Good suggestions and thoughts about sand. Tnx.

One question. On the top layer (above the membrane) if I have minor flaws, can I fix them with thinset or whatever tile mortar I'm using or does this add an unwanted layer preventing normal moisture travel from the tile above? Tnx.

Jim Cordes
07-24-2014, 11:05 PM
Nope skimming top mud bed with regular thinset wont trap moisture, remember you will be doing it when you set the tile anyways.

generally we(or rather I) don't bother skimming with thinset, just set the tile, however in some cases I will skim it and that is if due to the way I plan to tile the shower it would involve me working directly on top of the mud. a skim coat will help protect it from damage,

I don't do many traditional showers these days but still do alot of mudbeds, most mud I do now gets waterproofing directly on it and uses bonding flanges in lieu of clamping drains. especially in high end jobs because mud beds are so much more accurate and level then foam pans that are only true if the floor is perfect or the drain is perfectly centered...

The mix I use for small jobs. in a five gallon bucket add two shovels sand,one portland,two more shovels of sand, dry mix it together with mortar mixer , then about 2/3 coffee can(water adjusted depending on how wet the sand is already since the brick yard stores it outside), mix till it looks good

07-24-2014, 11:09 PM
Dave, you want that final mud bed ready to tile when you finish placing it. You don't wanna be having to "fix" that one with thinset mortar.

My opinion; worth price charged.

07-25-2014, 01:46 AM
Thanks for the feedback. I'm now more comfortable with making/working the mud but, for the tile layer, (and from my pre-pan experiences) I'd like to decrease my working time to get a more consistent pack and screed since I'll still be slow (relative to most all of you) even when this shower is done.

Because I'll need to mix up to ~1.5cf, I'd thought perhaps ..... pre-mix-dry several batches (with known amount of water to add) then pack them one after the other: fast-wet-mix, pack, screed and repeat. Mixing smaller batches is faster than large quantities. With my earlier attempts, packing well and getting an accurate screed takes more time than I'd thought. Some suggest 30 min max for the whole install, and I suspect that is really true, but I have a hard time getting good results in that time.

Another idea is pre-mix dry in smaller batches (to get a good mix) and then wet-mix each and leave each in buckets where the exposed surface area is smaller so it will won't start to dry as much -- and then dump, pack, screed and repeat so as to avoid delays in wet-mixing. Perhaps pre-mix a slight bit wetter for the 'batches-in-the-queue" -- except maybe that isn't worth the added risk of cracks.

I've read of many variations used by pros, and I'm sure they probably work well for each, but I'd also guess that something like the above might be more "forgiving" for a novice. Yes, might need to skim-coat for protection. Just wanting to avoid chipping out a top layer with a membrane installed. Again, thanks for the feedback.

07-25-2014, 08:31 AM
I guess I just got lucky...... 1) I used aprox 3 bags of topping mix + about a bag and a half of general purpose sand. 2) dry mixed it ALL inna wheelbarrow. 3) put the hose on it to wet it. How much water? I have no clue, but it was a hell of alot more than any 8 cups or whatever. I'd guess over a gallon or so. It was nice and moist and packed well. Not too wet. 4) Hauled it in with a 5 gal bucket. Many trips back and forth. 5) I spent well over an hour shaping and packing the top layer. No problems at all. I did both layers this way with no help at all.

07-25-2014, 08:36 AM
Just wanting to avoid chipping out a top layer with a membrane installed.

If the proper ratio of sand and topping mix are used with the right amount of water, you shouldn't have to 'chip' it out if needed. Hit it with a hammer and it will come out fairly easily....

07-25-2014, 09:07 AM
Mixing deck mud,concrete,grout,mortar and plaster is more of an art.You get a feel for how much water to add depending on weather,temperature and application.

07-25-2014, 09:20 AM
:goodpost: agree.

Jim Cordes
07-25-2014, 02:34 PM
Dave, generally if you have one guy mixing for you while your working the mud after the first batch that you mix together(demo) he should pretty much stay caught up to you..more or less.

07-28-2014, 01:59 AM
Thank all for the comments. This is a solo job so I'll probably pre-mix wet in several bucket batches with slightly more water than my 10(s):2(c):1(w) mix (maybe 1.5w) to give myself a bit longer working time. The 1(w) mix is quite dry (like the posted descriptions) but material not packed within 15 min no longer wants to pack very well. I'm assuming the top layer may actually be easier in some ways than the thinner pre-slope. First must finish the membrane and leak-test phase so I'm not needing to rush things. Glad I don't need to make a living at this ;-)

07-28-2014, 09:04 AM
Dave, you absolutely do not wanna add more water to your deck mud mix in hopes of making things easier. It'll be just the opposite.

I would recommend you go to Contractors Direct and purchase a Bucket Mortar Mixer.


I then recommend you dry-mix enough mud to do the job plus at least half a bucket more and stage those dry-mixed buckets near the shower. Add water to the first two and mix (takes maybe a minute per bucket). That will give you a good idea how much water you need for the remaining buckets and you can have pre-measured water for those.

Spread slurry. Place mud. Mix mud. Spread slurry. Place mud. Repeat as necessary. You'll find it works out rather smoothly.

I work alone about 99.9 percent of the time and use that proceedure successfully. The bucket mixer makes life sooooo much easier.

My opinion; worth price charged.

07-28-2014, 05:12 PM
Aha! The answer to my query about sequential wet-mix of premixed dry in buckets vs pre mix wet in buckets. Thanks; the formula is becoming more clear.

Version 3:
- Mix ratio: 10 sand : 2 cement : 1 water -- never mix wetter
- For larger quantity, pre-mix-dry with known volume (so added water is known)
- Wet-mix a batch and place - always thicker than wanted
- Pack down once - down to a little above 'the line' - edges first
- Screed flat to match required slope
(If surface too low, scrape out the pack and do over -- don't add mud)
- Mix next batch and repeat.
- Once screed is accurate, trowel to smooth surface

Does this match the requirements better?

Jim Cordes
07-28-2014, 05:19 PM
sound about right, all your batches should be pre-mixed dry that way you know they are mixed good. Do as CX said about the batches.

Also you should have more time then 15 minutes per should be more like at least 30 min or more before it dries too much, by your self you will be busy keeping up but you should still be safe with time..even if you mixed them one at a time it can be done.

07-28-2014, 09:41 PM
Dave, you're not gonna know how much water to mix in your batch until you've mixed the first one. The moisture content of your sand will make a significant difference in the water requirement.

Have you reviewed the article titled Deck Mud in our (Liberry)?

07-28-2014, 10:01 PM
CX, True, the moisture content can vary (as with humidity) but the sand is all dry packaged sand and the ratio of 10(sand):1(water) clearly suggests that humidity variations will only account for a very small fraction with dry packaged sand from HD. For sand from an outside yard, I'd agree. Cheers.

07-29-2014, 08:17 AM
Hmmm..... It ain't dat complicated..... :crazy:

07-29-2014, 11:38 AM
When I did my pre slope I mixed one bucket at a time.

I started out at the walls,once I had the proper depth and all sides were level I worked towards the drain checking the pitch.

It was a slow process mixing the mud by hand.

Looking back I should have had a helper mixing or the Bucket Mortar Mixer.

Jim Cordes
07-29-2014, 06:23 PM
Like CX said the water will vary..porous sand just in itself can effect that. no written in stone amount of water will work for all conditions and types of sand.

And I have found, as I suspect many other guys have found, that sand and cement ratios also seem to change depending on the sand. so hence you start to see why many long time mud guys don't really have a set formula they use everytime.
It is a feel that you learn over time, it is not that mud guys are lax in the way they mix, it is that they adapt the mixture for better working mud. and many times this means the first batch ratio might need adjusted for the next batch.

Can you see why that after thousands of years of deck mud that no one has a prefect formula. I would worry less about finding the perfect ratios and more on how to change change the formula, on the fly, to get it more workable...ex. more sand next batch,more cement next batch, more/less water next batch..not a perfect way but the best we can do with so many variables.

07-30-2014, 02:04 AM
Jim, agreed; there are enough variables but IMHO (where each project, like this one, has sub-projects which are new, it's really nice to have a starting point that is close -- like when using dry bagged cement and sand, the sand:water ratio that might be a little dry rather than too wet. When you don't have a natural feel for it from year of experience, a hint is very helpful.

Just did a thinset skim-coat of pre-slope #3 improved the surface (except for the thinset roughness in placed - needs a bit of scrape or sand) and, I think, close to flat. Checks with the level show a little variation but always downhill.

Once the thinset is cured, I'd thought about gently pouring water on the surface in various places as proof there are no valleys. Is this likely ok for the thinset skim-coat? Just thought it might be good to know of any residual surface flaws before installing the PVC liner. If I found a slight dip, can I just fill-in with more thinset? Thanks.

Jim Cordes
07-30-2014, 02:21 AM
No need to test on bare cement,no need to trap water under the liner,and absorbant cement might not tell you anything anyways.. go ahead and install the liner, then test it for drainage and do a flood test. If it fails the liner can always be pulled back up and low spot fixed. You should be alright though if you checked it good with level.

Need help on liner? remember to use a bead of silicone on the underside of liner at drain,none on top. fold all corners with no cuts, three inches above curb,recess wall studs to allow for liner, nail on outside of curb ONLY. pre-bend metal lath to fit over curb with tail going into pan for the second mud bed to stick to..again only nail on outside of curb

07-30-2014, 08:22 AM
And when making the folds at the curb, put the "ears" on the curb side, not the wall side. This way you can bury the folds in the fat mud going over the curb. Pictures start at post 116 for this

Jim Cordes
07-30-2014, 07:00 PM
I sometimes leave a space between the wood curb and the wall studs and shove the ears in it,,same with inside corners..leave the studs gapped and shove it in there..makes for a neat job.

Brian blackburn
07-31-2014, 11:26 AM
The OP is back – someone really hijacked my thread:talk: That's ok - lots of good discussion.

I realize I made a mistake in my first post. When I said I added 6 cups of water to the 60 lbs of sand topping mix plus 25 lbs of play sand, I didn’t think about the size of the “cup.” The “cup” was actually a plastic drinking cup that holds about 12-14 ounces (I don’t remember if I had it full to the brim when I added the water). So 6 “cups” would have been about 70-80 ounces of water, or a little over half a gallon. Based on other posts in this thread, regarding the 10(s), 2(c) and 1(w) ratio, I think the water I added was about right. As I mixed the mud, I added one “cup” of water at a time and mixed it thoroughly until the mixture looked and behaved just like what is described in the dry pack article in the “liberry.”

I tore out the floor and I am going to redo the pre-slope layer. I have been working on other stuff and haven’t done the second try yet – that is a project for this weekend. When I tore out the floor, it came out very easy. I didn’t use thinset on the concrete slab, so the dry pack wasn’t stuck to the slab at all. I didn’t have to chip it out. I dug a putty knife into the loose parts, all the way down to the slab, slid the knife under the dry pack and lifted out big chunks. Some of it came out in good sized chunks, and some of it was dust and I had to sweep and vacuum it out.

John Bridge’s article mentions that he has no trouble achieving 3000 psi compressive strength with this very dry mix. Much of my floor came out as dust, with obviously no compressive strength at all. Even the parts that came out in whole chunks are very soft. They are over an inch thick but I can break them in half easily with my hands. If you drop anything on them, they crumble. The whole pile of debris has been lying on my garage floor since I tore it out, nearly 3 weeks ago, and it is still as green as the day I poured it.

What bothers me the most is that I am not certain what to do differently on the next try. I followed the instructions on this forum, and the mud behaved as instructed, but I still think I used too little water. Plus I think the slab sucked the water out of the dry pack. I dampened the concrete slab before laying the mud, but I didn’t use thinset. I also probably worked with the material too long. By the time I was finished with a section, it had definitely dried out, and I don’t think it would hold its “snowball” shape any more. The only thing I can tell I definitely did wrong, based on instructions on this forum, is that as I packed and screeded the floor, I added thin layers of additional material to fill in low spots.

When I tore out the floor, there were two places where the pack was strongest and where it came closest to bonding to the concrete slab. The first place was the first place I dumped in mud, so it would have been the wettest. The second place was the last section I worked. My wife mixed new material as I worked on the floor, and on the last batch, she added 7 cups of water instead of 6. So all this still makes me think my mix was too dry.

So when I try it again, I am going to use a little more water, I am going to trowel down a layer of thinset on the concrete slab, I am going to work faster, and I am going to pack it all in once, then screed, and not add any new material. Hopefully it will work better this time.

I have some unrelated questions about tiling the walls.

The shower walls to be tiled are covered floor to ceiling with Hardie Backer 500. I didn’t put any moisture barrier on the studs before installing the hardie backer. The cement boards are screwed directly to bare studs. Before I found this forum, another “expert” told me I didn’t need moisture barrier, and he said there are actually reasons why it is a bad idea. So was this a serious mistake? Do I need to take the boards down and put moisture barrier over the studs, behind the cement boards?

Also, I bought Laticrete Hydro Barrier and their anti-fracture membrane fabric to seal the cement boards at corners and niches. I have never used this stuff before, but it seems like an easy-to-use product. I have reviewed the installation instructions and the videos on the Laticrete website. I hadn’t planned to paint the entire surface of the boards – only the joints and corners. Also, the instructions for Hardie Backer don’t require the entire surface to be waterproofed. But then I thought I might as well paint the entire surface, and that could also offset the fact that I didn’t put moisture barrier behind the cement boards.

Since I have never used the Hydro Barrier before, I did a test and painted a scrap piece of hardie backer. I am a little concerned about covering the walls with this stuff and then expecting it to bear the full weight of all the tile, since the tile is glued to it instead of the cement board. After it dried, there were no bubbles or holes, wrinkles, or loose spots. It looked nice and smooth and ready for tile. Out of curiosity, I scraped at it with my finger and some tools, to see how firmly it was bonded to the cement board. When I scraped at a corner with a knife, I was able to raise up the corner, and then I was able to peel off the entire sheet in one piece. It didn’t seem like it was bonded that well to the cement board. I know that nothing will be peeling at the corners with a knife once the tile is installed, but I would have preferred that it was harder to peel off.

• Is there a problem painting the entire surface of Hardie Backer with Hydro Barrier before setting tile?
• Do I need to take down the cement boards and put up moisture barrier, or will the Hydro Barrier be sufficient?
• Should I be concerned about being able to peel off the Hydro Barrier?


07-31-2014, 11:58 AM
You can use either plastic behind the Hardibacker, or Hydrobarrier on the surface of the Hardi, but not both.

Your question raises a question for me: You don't have the liner in yet, but you have Hardi on the walls, correct?

Brian blackburn
07-31-2014, 12:18 PM
I wanted to do everything in the shower that required a ladder and tools before working on the mud and liner, so I started from the ceiling down and installed the ceiling sheetrock and 2 rows of hardibacker boards. The only thing that isn't finished is the bottom row of cement boards which I will install after I finish the floor.

07-31-2014, 12:42 PM

Don't worry about the plastic on the studs, as long as you cover the entire wall with hydrobarrier, not just the seams.

Check the installation instructions for hydrobarrier and see if it says anything about a primer coat, which is typically an application thinned with water.

Brian blackburn
08-01-2014, 09:03 AM
No, the Hydro Barrier instructions don't mention a primer coat. Only thing it says is that the stuff "can" be applied over a damp surface.

I will test a thinned primer coat and see if it makes a difference.

Any reps from Laticrete have any comments?


08-01-2014, 03:41 PM
Check with Technical support on that, Brian. I wouldn't thin it unless they okay it. 1-800-243-4788 x235 or

Brian blackburn
08-16-2014, 08:12 AM
I redid the pre-slope floor last night and I think I have a keeper. I used a layer of thinset on the concrete slab before I packed down the mud, and I was able to work a little faster (but not much) since this was the second time. I used a wood float and I was able to pack the mud down better than last time. Last time I said I used about 70-80 ounces of water to 60 lbs of sand topping mix and 25 lbs of play sand. This time I used about 100 ounces of water to the same materials. It was obviously wetter, but it worked ok. There are a few small holes or low spots in the floor, but those I can easily fill and smooth out with thinset before putting down the liner.

I plan to let the pre-slope set about a week, then lay down the pvc liner and pour the top layer, and then let that set awhile before setting tile.

I also plan to build a bench across the far end of the shower, from cement blocks. It will be the full shower width (46"), about 12" deep and 16-18" high. I was planning to build it on top of the final mud layer, but the article and pictures in John Bridge's "Tile Your World" book show the bench built on top of the pvc liner before the final layer of floor is poured. I wanted to work on top of the floor instead of the liner so that the bench could be mortared to the floor as well as the walls, and so that I don't risk tearing any holes in the liner as I do the bench construction.

Is it important which comes first, bench or top mud layer? Is there a reason why the bench needs to be installed directly on top of the liner?


08-16-2014, 08:18 AM
Brian, your mud would be a lot happier if you covered it with a polyethylene sheet when you finished forming it. I'd recommend you do that now.

You want to build your "monument bench" on top of the liner so your final mud bed is formed using the bench front as one wall and allowing you to make the perimeter of the shower footprint level all around. You can build the bench on top of the final mud bed, but that will cause the perimeter to lower at the bench front and potentially upset your wall layout.

I recommend you abandon those plastic divider strips in your final mud bed.

My opinion; worth price charged.

Brian blackburn
08-16-2014, 12:25 PM
I just covered the floor with a plastic painting drop cloth - that's the only sheet of plastic I have available. it is weighted in the corners and stretched out pretty flat, but it isn't taped and sealed all along the sides, so its utility might be questionable.

Should I wet the floor, and then re-cover it, or just leave it covered as is for a few days?

08-16-2014, 03:07 PM
Wouldn't hurt to dampen it a little, but it should be OK as it is unless it was allowed to dry significantly before you covered it. Doesn't need a perfect seal around the edges at all.

Are you seeing some condensation on the underside of the plastic drop cloth?

Would help if you'd put a geographic location in your User Profile so we could see where you are and guess whether your AC is turned on. :)

Brian blackburn
08-16-2014, 04:08 PM
Floor dried for about 18 hours before I covered it (didn't know I was supposed to cover it). No condensation showing on underside of plastic currently. I am in Houston. AC is on, 77 degrees in the house.

08-16-2014, 05:11 PM
Would help if you'd put a geographic location in your User Profile... If you don't do that it'll be lost before we leave this page.

Wouldn't hurt to dampen that mud a bit and cover it.

Brian blackburn
08-17-2014, 07:08 AM
Profile updated as requested.

I sprayed water over the floor right after our last posts yesterday and recovered it. I will leave it covered for about 3 days, then move on with an attempt at installing the liner and top layer of mud.

What should I use to seal the pvc liner to the floor flange?


08-17-2014, 12:56 PM
I like to use 100% silicone for sealing pretty much everything. Since the purpose of it is to keep moisture from getting underneath the liner, you want something that will hold up if you have a sewer backup. The latex acrylic caulk products aren't really made to hold up in those conditions.

05-17-2020, 10:28 AM
Hi, I found this thread trying to analyze my mud deck failure on my first tile shower..I was totally dejected while breaking up the floor with a hammer. :bonk:
After reading thru this thread and adjusting my mix (I am using pre-mixed 4:1 Mapei mud mix) with just a little more water, mixing a bit more thoroughly, and doing the entire thing at once (no adding of material after packing, try to be done in 30-45 mins), and covering with a tarp, it seems like my 2nd try has held up. This definitely an art.
I also see someone else (Homie the Clown), has a floor pan project and he is a few days ahead of me in his thread..
I will go read up on that one too, but this thread helped a lot with educating me a bit.

05-17-2020, 11:08 AM
Welcome, Shawn. :)

Best to start a project thread of your own if you have any questions for us. You'll get lost and we'll get confused if you try to use another member's project thread.

05-17-2020, 11:24 AM
CX, Roger that..I was just commenting that this thread helped me not get totally frustrated. Haven't made enough progress to have any real questions of my own yet!! :)