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Unread 06-14-2021, 09:18 AM   #1
atw58
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Crumbly Top Pre-slope Layer

Building a 4x5 ft basement shower over concrete. I laided a pre-slope shower pan base with 4:1 ratio of construction sand to Portland cement. One day later the top 1/32 is very loose and comes off easily. Below the loose sand it is hard with more cement look. Photo shows 3 spots where I rubbed the top sand off. There's a few hard chunks in the loose sand but most feels like a slightly coarser version of the original sand.

Dry sand/cement was blended by hand first to a uniform consistency then mixed by hand with minimal water to stay in a ball when squeezed. Used a small hand trowel to mix 66 lb bag of sand plus cement and water so it took 20-30 min to reach final consistency.

Any ideas of what went wrong, did I mix too long, overwork tamping the mud. Can I proceed with the pvc liner after taking off the loose layer.

Also the thickness near the drain is 3/8 inch. Is this too thin.
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Last edited by atw58; 06-14-2021 at 09:21 AM. Reason: Another question added.
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Unread 06-14-2021, 01:21 PM   #2
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Art....You may well be OK with that. Use a vacuum with a brush to remove anything loose and then flat trowel a smooth layer of thinset over everything. The preslope only needs a slope to drain properly. It doesn't need to be "purdy."

The final slope should be smooth to tile upon......
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Unread 06-14-2021, 02:25 PM   #3
atw58
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That's a relief. I have some left over Ardex FF which could work to smooth things out too but thinset is more economical.

Still would like to know what the cause was to avoid the same on the final layer. Hoping folks encountering the same problem chime in.
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Unread 06-14-2021, 03:45 PM   #4
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It happens all the time. The mix probably needs to be a little wetter (but not much). Plus, when you get finished screeding the mud, slick it down with a flat trowel. That will bring a little moisture to the surface causing the mud to get harder on top.
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Unread 06-14-2021, 09:11 PM   #5
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Your 20-30 minute mixing time ate up a good chunk of the mud’s working time.

For top mud bed set up several buckets (or a giant mixing tub), dry blend the ingredients, portion it out to the buckets and have the water measured out assembly line style. You really want to get the stuff mixed, placed, packed and screeded fairly quickly. A bucket mortar mixer and 1/2” drill would make quick work of mixing it up, but the $80 or so on the mortar mixer might be too much to spend.
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Unread 06-14-2021, 09:18 PM   #6
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The pre-slope was done over 2 days such that 2/3 of the rectangle was laid one day and the rest the next day (bad idea). The 2nd day's mud did not stick to the first day's and the joint between the 2 flaked off.

The hard bottom appears full of cement and the crumbling bits was all sand. Couldn't see any cement in the loose portion. To me sand and cement was mixed well when dry and well after adding water. Don't know why the cement wasn't uniformly distributed from top to bottom.
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Unread 06-14-2021, 09:21 PM   #7
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Sorry, I didn't see Lou's reply before leaving my last post. I didn't realize the working time was so short.
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Unread 06-18-2021, 05:32 AM   #8
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Crumbly Pre-slope Solved

As a test, I quickly mixed a small amount of 5:1 sand/cement and packed it in a cookie tin. Next day the surface was perfect. No loose bits, held its shape, firm and colour was the same as wet.

I'm convinced the problem was taking too long to mix and lay the mix.
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Unread 06-18-2021, 05:57 AM   #9
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Alino Membrane And Redgard

Now on to preparing the walls for tile using Densshield on walls, Alino membrane (fleece) and Redgard. Here are the intended steps:

1 - 3 coats of Redgard on the Densshield plus 2 more at drywall screws.
2 - Apply modified thinset, notch, imbed membrane with 2" overlaps as recommended and reinforced corners.
3 - 3 more coats of Redgard.

I know I'm mixing systems but hope to get comments before proceeding.
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Unread 06-18-2021, 06:22 AM   #10
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What do you hope to gain by not using a single proven system?

As far as I know, any kind of drywall is not a suitable substrate for RedGard.

I imagine you're looking at it as a belt and suspenders approach, but you're effectively defeating the design engineering in every product.
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Unread 06-18-2021, 06:47 AM   #11
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Art, it'll help if you'll keep all your project questions on one thread so folks can see what you're working on and what's been previously asked and answered. A moderator can give it a more generic title any time you'd like to suggest one.

Is this the AlinO product you plan to use?

If so, why the RedGard? Or the DensShield, for that matter? While I've never seen or hear of the AlinO product, it appears from the minimal information I've found that it is similar to other sheet-type waterproofing membranes (ANSI A118.10) that are installed with thinset mortar. I have not found any information indicating that the product meets that standard, though.

In any case, why would you be trying to install it using RedGard? Let's start there.
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Unread 06-18-2021, 09:01 AM   #12
atw58
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Yes, that's the Alino product I have. It's sold here in Canada at our Home Depots.

My thinking is there will be 3 levels of protection: Redgard on drywall then Alino membrane and Redgard before thinset/tiles. Depending on the opinion Densshield is water resistant not waterproof. I'd rather use that than cement board.

The mix of materials is due to what I have on hand and each product seems to have good reputations.
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Unread 06-18-2021, 10:52 AM   #13
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It can be very helpful to put that geographic location into your User Profile, Art. Frequently makes a difference in answering some types of question.
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Originally Posted by Art
...and each product seems to have good reputations.
In which case I refer you to Peter's comments in post #10. Pick the waterproofing product you want to use and use it per the manufacturer's instructions.

My opinion; worth price charged.
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Unread 06-20-2021, 10:02 AM   #14
Davy
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I think you would have been better off to use cement board with Redgard over it.

I've never tried one waterproof membrane over another but you could possibly have bonding issues. If you want more layers of protection, apply another coat of the same product if their instructions call for it. Redgard for example usually takes a primer coat and a couple coats straight from the bucket. Follow the instructions of the product you use.
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Unread 06-26-2021, 08:58 AM   #15
atw58
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Epoxy Floor Over Deckmud

I'm looking for a flooring system for a 4'x5' basement shower with linear drain and not satisfied with mosaic or large format tiles. My wife suggested an epoxy floor coating maybe the same as those garage floor kits.

Is it possible to apply epoxy over sloped deckmud or deckmud with a layer of thinset.
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Last edited by atw58; 06-26-2021 at 09:12 AM.
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