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Unread 04-05-2020, 07:25 PM   #1
Florichusetts
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Acrylic Shower Pan Uneven Mortar Bed - Grinding

Need advice on next steps.

First time putting in a shower base. Used a Dreamline Slimline alcove shower pan to replace a fiberglass tub. Second floor install on (assumed 3/4"?) plywood subfloor that sloped +- 1/2" away from the drain was but pretty much level front-back. Ripped +-1/2" board to get pan level, then set the pan in a bed of dry pack.

Achieved ratio of 5:1 using topping mix and play sand and added water in a concrete mixer until I could just form it in my hand. I filled the pan area with mortar, but used too much and had to remove some twice before getting down to my pencil lines on the third try. Left it alone for 24 hours before walking on it.

The problem is that I can hear a bit of grinding when I step in the pan. The centerline on the drain feels great, with barely any sound, but walking on either side (along back and curb) creates that sandy noise, like the pan has a tiny bit of leeway. It doesn't feel like it's giving at all, but I can see one spot on the back wall where it gives a little under my weight (150 lbs). I pulled up lightly on the curb and it's pretty solid.

Did I do something wrong? Can this be fixed? This is for my SO's mother, and she's not happy with the noise. I think she thinks it's going to crack or something. Any advice is greatly appreciated.
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Unread 04-05-2020, 09:15 PM   #2
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Welcome, Page.

While you appear to have followed the manufacturer's instructions, I think you used the wrong selection from their recommendation of materials to use for your bedding mortar and then made it a bit worse by mixing it the way you did.

Quote:
Originally Posted by Dreamline
5. Mix the bedding material (Mortar,
cement-sand mix, etc.) Concrete
or plaster is not recommended.
Apply enough bedding material
to support the entire bottom of
the shower base. This will add
additional stability and prevent the
base from shifting position.
A "cement-sand" mix is going to act differently from a "mortar" mix, especially if you mix it like dry-pack, which is what you did. A sand/cement mix might have worked if you had mixed it according to the instructions on the bag, but still would not have worked as well as would a mortar mix or mason's mix, which will contain some lime along with the Portland and sand and will, to use the very technical term, moosh a lot better in your application.

I would recommend you remove the receptor, clean up the bottom if at all necessary, as well as the floor, and re-install it with a more appropriate mortar mix. I think you'll be a lot happier with the result.

My opinion; worth price charged.
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Unread 04-05-2020, 09:34 PM   #3
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Since the bottom of the tray is not likely perfectly flat, it usually works better to make lots of piles of the mortar and then push the pan into it, leveling as you go. If it's relatively plastic, you can get it to squish in place, filling in between the piles to provide good support.
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Unread 04-06-2020, 09:12 AM   #4
Florichusetts
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Thanks CX. New questions for you and Jim:

- I was under the impression that a deck mud/dry pack was the correct material for setting an acrylic receptor? I went for the topping mix/sand method off the John Bridge How-To - Deck Mud page. What would be the more appropriate mortar?

- What are the chances I can pull up this receptor without damaging it? I didn't pull hard, but it's pretty snug in the bed.

- If I use a "more appropriate mortar", would Jim's suggestion of applying it in multiple piles, rather than a full bed as I had done, still help?
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Unread 04-06-2020, 11:40 AM   #5
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Not an application for deck mud at all, Page.

Your receptor manufacturer wants the entire receptor supported by the mortar. Without seeing the bottom of the receptor, I can't say whether individual piles of mortar would be an appropriate approach or not.

My opinion; worth price charged.
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Unread 04-06-2020, 04:41 PM   #6
Florichusetts
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Bottom of Dreamline Pan

CX, attached is a picture of the bottom of the pan. The circles closest to the drain are +-1/2" tall, and those at the far end are +-3/4" as it follows the slope of receptor.

Technically this is a fiberglass reinforced acrylic base. TBH I've read all sorts of different solutions for what to set this type of pan in (or if it should be done at all) from plaster, to structolite, to dry pack, to mortar.

I know there are many means to one end...and seeing as I'm not happy with this way I'd like to try something better.
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Unread 04-06-2020, 05:55 PM   #7
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For full support, I'd spread the mud over the entire area (except for the drain, of course) to the depth of those round feet on the bottom of the pan, plus a tiny bit more. You want the mortar loose enough that it'll push into every area and the excess will squeeze out, in necessary.

If you get it a little thick in one area, you can lift the pan back out and remove some before it gets dry, and reset the pan.

I would put some plastic over the plywood floor to keep the mortar from drying out too quickly and cracking. It may or may not help, but it can't hurt.
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Unread 04-07-2020, 11:17 AM   #8
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Apparently all the base needed to come out was a bit more elbow grease than I could muster. Not much to clean up on the bottom, thankfully.

My local Lowes has Mapei's 4-to-1 Mud Bed Mix says it's ideal for floating shower bases. Would anyone suggest a different product?
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Unread 04-07-2020, 02:42 PM   #9
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One of the few real good applications for Quikrete Mortar Mix (1102) from your local Home Depot.

My opinion; worth price charged.
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Unread 04-07-2020, 04:42 PM   #10
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Ok. Since my HD dosn't seem to have the Quikrete in stock for whatever reason, and Lowes only has it in 10lb bags, I'm assuming that the Sakrete Type N mortar is a suitable substitution?
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Unread 04-07-2020, 04:47 PM   #11
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Yes, and again, one of the only suitable applications for a Type N mortar in my book. I think you'll find it quite satisfactory for bedding your receptor.

My opinion; worth price charged.
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Unread 05-23-2020, 03:11 PM   #12
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So a month and a half has gone by and we finally got the pan reset, this time in a bed of type N mortar. Seems to be much more solid this time. Thanks CX!

The silver lining in all this was that I looked at the instructions for the shower door we purchased and realized that it's frameless, i.e. no out-of-plumb adjustment, so before we reset the pan I sistered a bunch of studs to the old ones, cut shims, and now have perfectly level end walls (they were a good 1/2"-3/4" out of plumb before, leaning out). If Armageddon happens this shower isn't going anywhere.

Now I have some cbu install questions:

- I've seen many install videos where there is no blocking along the cbu edges...Durock says to continuously support the edge. I plan on doing this since I have the studs for it, but is it overkill?
- I plan on using Durock screws 8" o.c., then self-adhesive fiberglass mesh tape on the seams, then thinset over the tape. Holding cbu 1/8" off the top of the receptor flange per the receptor install instructions.
-How do I protect the gap between the cbu and the receptor flange?Is it not necessary since the tile and thinset sit in front of and below this joint?
- I have Aquadefense liquid waterproofing to seal the walls. Sal DiBlasi uses a reinforcing fabric on corners...how important is that step? Why is the mesh tape and thinset not enough?

Thanks!
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Unread 05-23-2020, 03:21 PM   #13
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Also, the back and fixture end wall have existing ComfortTherm insulation that has as a vapor barrier (they are exterior walls). Is this going to be an issue when I add the Aquadefense? There are several rips and holes in the vapor barrier that I was going to fix with tape, but if the aquadefense will act as a second barrier (and that's not an issue) then I won't bother fixing the rips.
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Unread Yesterday, 08:10 AM   #14
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Page,

No, the extra studs to pick up the ends of the CBU are not overkill. At all. You want the seem where the CBU meets the drywall to be solid.

If you are not going to shim the CBU out so it can drop down over the flange then I would just caulk the joint with silicone.

If you are going to reinforce the CBU seems and corners with CBU specific mesh tape (not drywall mesh tape) and thinset mortar I don't believe you need additional mesh tape, but best to confirm with Aquadefense installation instructions.

You're correct, you don't want to trap moisture between the back of the CBU and the face of the insulation. Use a utility knife to make a bunch of slices in the facing.
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