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Unread 07-14-2014, 09:10 PM   #1
Brian blackburn
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Problems with dry pack shower floor

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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Unread 07-14-2014, 09:52 PM   #2
dhagin
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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.
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Unread 07-14-2014, 10:07 PM   #3
Kman
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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.
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Unread 07-14-2014, 10:49 PM   #4
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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.
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Unread 07-15-2014, 08:23 AM   #5
04Rdking
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Quote:
I added 6 cups of water....
6 cups of water to
Quote:
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.
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Unread 07-15-2014, 10:38 AM   #6
Brian blackburn
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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.

Thanks,
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Unread 07-15-2014, 10:52 AM   #7
04Rdking
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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.
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Unread 07-15-2014, 12:56 PM   #8
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Pre-Slope

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.
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Unread 07-15-2014, 05:39 PM   #9
Brian blackburn
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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.
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Unread 07-15-2014, 06:06 PM   #10
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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.
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Unread 07-15-2014, 06:33 PM   #11
Brian blackburn
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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,
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Unread 07-15-2014, 06:50 PM   #12
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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.
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Unread 07-15-2014, 08:08 PM   #13
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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.
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Unread 07-15-2014, 10:11 PM   #14
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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.
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Unread 07-15-2014, 10:12 PM   #15
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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?
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