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Unread 10-07-2013, 05:46 PM   #1
jjdike
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waterproofing drop-in tub deck for granite covering

I am working on a remodel in which I have a large drop-in tub framed and am ready to start working on the waterproofing measures. The tub deck is surrounded by three walls. I have the tub deck frame covered by 3/4 in plywood, with 1/2" thick hardibacker cut and ready to install. My understanding is that I should place a plastic water barrier like 4 mil poly sheet on the walls underneath the wall hardibacker. Hardibacker instructions for floor say to use thinset on plywood plus screws to attach the hardibacker, so that was what I am planning for the tub deck. My question is do I run plastic sheet from the walls over the tub deck down to the floor? If so, does it go under the mortar, over the hardibacker, or installed in some other way?

I will be using two pieces of granite seamed length-wise at the ends as the deck material. A second question is how should the granite be connected to the hardibacker?

Thanks for any suggestions.
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Unread 10-07-2013, 07:38 PM   #2
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Hi Jay. Please tell me this tub has no shower head.
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Unread 10-07-2013, 07:40 PM   #3
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Welcome, Jay.

Will there be a shower associated with this tub installation?

If not, you're not technically looking at a wet area installation. If you want to consider it a wet area, that's fine and you're the one gets to decide.

But if it's a wet area, you're not gonna be able to waterproof it by the method you describe. You'll really want to use a direct bonded waterproofing membrane, sheet or liquid applied, over the face of the wallboard and the tub deck. And wherever else you think might get wet.

James Hardi would recommend the thinner HardiBacker for the horizontal surface and I'd want mine installed just like on a floor, with a thinset mortar bed under it and the appropriate mechanical fasteners. Use of the thicker Hardibacker is OK, just not necessary.

I would set the granite in an appropriate thinset mortar.

[Edit] Davy was axin' while I was typin', but we know there's no shower. Really we do.

My opinion; worth price charged.
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Unread 10-07-2013, 07:43 PM   #4
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Seems like every time I assume there's no shower head, there is.
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Unread 10-07-2013, 07:49 PM   #5
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I use paint on liquid elastomeric waterproofing membrane (Redgard, Aquadefense, Hydroban etc.). It goes on top of the cement board and 6" up the walls. No Poly anywhere except on exterior walls. Let the slab guys install the stone for you. There is just too much of a chance to break it at the narrow point if you don't have experience handling it.

Personally, I'd not bother with the Hardi, and set the slab in LFT thinset applied with a 1/2" 'U' nothch trowel. Some slab guys just set it on blobs of silicone.
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Unread 10-07-2013, 08:33 PM   #6
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Thanks to all for the quick replies.

There is no shower over this tub. However, there is one in a large adjacent shower area though, so there is some potential from splash from that. Because of that and your advice, I think I will treat the tub deck as a wet area. The layout is the drop-in tub as described, adjacent to about a 4 1/2 ft x 8 ft open area with tile/mortar/liner/mortar on concrete shower pan planned (top to bottom layers). Currently there is no plan to block the tub area from the shower because of the relatively large shower size, but we might add a curtain later. I should have included this info in the initial question, but was more focused on the tub deck.

Reading up on the Aquadefense suggestion, I can find it here at Lowes, so I could go with that. So I could install the hardibacker on the walls and tub deck, then use the Aquadefense over that, then install the granite. Does that seem like a workable approach? Thanks again for the help!
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Unread 10-07-2013, 09:49 PM   #7
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Quote:
Originally Posted by Jay
So I could install the hardibacker on the walls and tub deck, then use the Aquadefense over that, then install the granite. Does that seem like a workable approach?
Using a liquid membrane over your hardi (tub deck and walls) is a very workable approach. If you go that route, skip the plastic behind the hardi. Also, not sure how the shower portion of this project is constructed (or how far along it is), but it would be best case scenario to tie the tub waterproofing into the shower waterproofing if they are connected..
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Unread 10-07-2013, 10:03 PM   #8
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Thanks for the feedback Brannnigan. I only have the preslope and liner down for the shower pan, waiting to resolve the tie in with the tub area, so I can definitely tie the two areas together.
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Unread 10-07-2013, 10:17 PM   #9
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pictures would really help

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Unread 10-07-2013, 10:22 PM   #10
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You may certainly waterproof the installation, and using a surface applied waterproofer such as Aqua Defense. Be sure the plywood deck is well supported. You could skip the hardie and just use Ditra on top of the plywood, which will also waterproof it sufficiently. Or use Hardiebacker. Your choice, but read below before choosing.

To install the granite slab, you can use a good thinset. DO NOT pre-cut the hole for the tub!

To start, use a good level to place horseshoe shims as needed at about 2 ft apart intervals, checking from shim to shim that they are all level to each other.

Next, choosing the area for one of the pieces, place blobs of thinset at no more than 12" apart, and near but not on the shims. The blobs should look like 1/2 a tennis ball for 1/4" shims, to a golf ball for no shims. Be sure to have blobs near the cut-out edges, and in particular at the inside corners (unless it is an oval shaped tub of course!).

Set the first piece, let it settle until it hits the shims by wiggling it.

Cut out the first piece for the tub cut-out, using a dry blade/ grinder. Have an assistant vacuum the dust as you cut using a shop vacuum. Have supports in place to stop the cut-out from dropping to the floor or on your feet (ouch!).

Place blobs for the second piece, like for the first, and install it while standing in the cut-out hole of the first piece. Let it settle.

Check the two tops for level, and the alignment from piece-to-piece at the seams. You can push-up on the low piece by running a screw up from the underside of the plywood tub deck. If you have used Hardiebacker, you may need to pre-drill a small hole through the deck/hardie or you may have a hard time getting the screw to penetrate the hardie. Carefully adjust until the match is perfect.

Resin the seams using a flowing type polyester resin. First color the resin to match the stone. Less colorant is better than more. Semi-translucent for most granites looks best. Stick a wood shim between the wall and the seam to dam it up, and tape at the open side. Add hardener, and drizzle the resin into the seam, using a razor blade to knife it into the seam, and feed it into the seam. Before it starts to set, push the two pieces together to tighten the seam by using wood shims stuck into the gaps at the opposing walls to shove the two pieces together and reduce the seam to as tight as it can get. Continue to feed resin into the seam keeping it filled with resin until the resin just starts to gel, then stop trying to move the resin. Let it harden until not "sticky" to the touch, then scrape the excess resin off the top of the pieces by scraping back and forth with a razor blade held vertically( just like scraping wood). The razor blade cannot scratch granite

Cut out the other tub cut-out in the second piece, same procedure as the first.

Tile the walls, or install granite slab splash. Caulk splash.

Install drop-in tub as directed by manufacturer.
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Unread 10-08-2013, 12:40 AM   #11
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Attached are a few pictures.

Marty thanks for the detailed installation instructions. Is the reason to not cut the tub hole out ahead of time to avoid breaking the granite while installing? I was thinking of cutting it ahead of time so I could do it outside with a wet cut saw, then carrying the pieces in on plywood to avoid breaking them and minimizing the carry weight into the room, but after cutting the slabs to rough size they will probably not be too heavy. I was going to do the seam at the ends of the oval cutout, so they would be short (less than a foot each) and run in the tub length direction.
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Unread 10-08-2013, 08:01 AM   #12
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Quote:
Originally Posted by jjdike View Post
Attached are a few pictures.

Marty thanks for the detailed installation instructions. Is the reason to not cut the tub hole out ahead of time to avoid breaking the granite while installing? I was thinking of cutting it ahead of time so I could do it outside with a wet cut saw, then carrying the pieces in on plywood to avoid breaking them and minimizing the carry weight into the room, but after cutting the slabs to rough size they will probably not be too heavy. I was going to do the seam at the ends of the oval cutout, so they would be short (less than a foot each) and run in the tub length direction.
Avoiding breakage is the reason. The percentages are that you may be able to cut outside and install without incident, but is it worth the risk? Also, 2cm (and even 3cm) granite "flexes", so installing as a whole piece then cutting leads to flatter installs. You will seam the exact same lengths as if you pre-cut, because you have already cut-out half, or all if you prefer (I cut the 2nd piece after seaming so I won't get the open seam packed with dust).

When we do undermounted tubs, we usually rod the pieces to make them handle able. As soon as you cut a piece into an "hourglass" figure or any larger-type cutouts such as sinks, the weakening factor is astounding. Rodding is like buying insurance, and for top-mounted anything you cut after setting for likewise insurance.

You haven't said what color granite. Some are stronger than others, but I would still do cut-outs after install. Like I say, it's the percentages. No gamble means no loss.

I would do it on any of the man-mades in the blink of an eye. Totally different scenario
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Unread 10-08-2013, 08:03 AM   #13
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Jay, you're gonna need to treat that tub installation as a wet area in that setup. You're even gonna wish you had the tub deck sloped to drain, but that poses other problems with the installation.

Has the person responsible for cleaning signed off on that design?

How 'bout a photo showing the shower entry and drain location?

My opinion; worth price charged.
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Unread 10-08-2013, 08:29 AM   #14
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Marty - the granite is 'Golden Venus', and is sort of a lighter color. I don't know if that is a standard granite name or not.

CX I will add a picture later, but the drain is about 32" from the back wall, 24" from the right wall, behind the vacuum in one photo. I have done a shower test and checked the slope for drainage. You are right about cleaning be a consideration - the thought is that we will run a shower curtain along the outside of the tub to minimize splash on the tub. There is a corner near the entry end of the tub where the curtain can be pulled to be past the tub and almost out of site. The idea was to go for sort of a more open area. I am not so far along that I couldn't add a bit of slope to the tub deck.

Thanks again for the input.
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Unread 10-08-2013, 08:34 AM   #15
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I took a good look at your pics. That back wall piece is going to break pre-cut without rods period. Even absolute black. Light colors break the easiest.

Be sure to firmly support the overhang in place on both pieces after setting and you go to do the cutouts. Unsupported the weight of the cut-out will snap that narrow waist before you finish cutting.

Last edited by MDtile; 10-08-2013 at 08:47 AM.
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