Under Mount Tub - Deck and Mounting

Discussion in 'Shower & Bathtub Forum & Blog' started by Jdavis37, Oct 12, 2013.

  1. Jdavis37

    Jdavis37 New Member

    Messages:
    29
    Location:
    NC
    Hopefully a simple question due mostly to my ignornace of the "how to" part..... but here goes:

    I am in middle of a complete gut master bath remodel and next week should see a ton of activity. I have been hampered by the size/layout of my room, having only 143 or so inches to squeeze in a tub, shower and toilet. I settled on a 60 inch tub (I am the bath taker and have long legs but found a tub with sufficient legroom in a 60 inch chassis).

    Tub deck was built late last week and we were able to maintain 34 inches for the toilet bay (after tile is installed) and have about 42 to 43 inches interior tub space (width), which is ahuge improvement from the builder installed peripherals.

    However, to do this, they constructed a deck with a 2 x 6 on the leading edge and 2x3's rest of way around. The tub will be an under-mount installation with granite on top. I am assuming granite installer will do granite in 4 pieces but have not yet verified. After seeing the deck I am having trouble seeing how the granite is going to work. I truly do not have the room to do 2x6's all the way around for the top but could have fit another one in opposite the one in place now. My gut feel says the deck as done now isn't going to work well as I am assuming the granite weight should NOT be on the tub itself but rather just the deck.

    This is where my ignorance is coming in and would welcome some expert comments. The tub top edge is approximately 3 inches wide . Thx in advance.
  2. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    Location:
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    Will this tub also be equipped with a shower?

    Installing the Granite over the tub often creates a weak point in either the strength of the tub deck or the waterproofing material. It is not uncommon to find slab installers using nothing more than construction adhesive to install these slabs.

    We have been recommending that the underside of the drop in tub be stiffened up and then a water proofing system used over top of the tub deck. On my last we lightly scratch the top of the tub deck and used a product called Ardex 8+9 over top. Some tubs have a tile flange you can purchase for waterproofing a drop in tub for a tub equipped with a shower. Either approach with an undermount look will require some steps outside of any recommended approach outlined by the TCNA.
  3. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    Location:
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    Last edited: Aug 26, 2014
  4. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

    Messages:
    4,690
    Location:
    North Vancouver, BC
  5. Jdavis37

    Jdavis37 New Member

    Messages:
    29
    Location:
    NC
    John,

    Thanks for the reply and I'll sift through things. First though, this tub does NOT have a shower. The shower is a stand alone shower adjacent to the tub deck.

    The concern I currently have is with regard to how much deck wood is needed to properly support the granite going above, At each end of the deck the amount of wood is about same width as the tub width. Intuitively just doe snot seem like enough wood to support the granite to ensure granite is not bieng supported by the tub.

    I am confident the mortar base beneath, etc will be done properly and may simply be over analyzing things and not trusting enough. That said, trusitng too much can have bad side effects! There may be ways to support the tub from underneath if needed but I'd rather avoid that when it seems more important ot ensure the deck is built properly to support the granite above it. John

  6. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

    Messages:
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    Location:
    North Vancouver, BC
    Before we set this tub we infilled the void under the deck mount portion. A coat of Ardex 8+9 on the inside was added as a bonding layer. Then we drove in a few screws to add strength.

    Once this was dry we set the tub onto a tub deck prepared with plywood top and cement board. We used thin-set to affect the bottom of the tub deck to the supports and also had mortar underneath. The top of the tub was rock solid at this point. You could jump on it with no deflection. The Ardex 8+9 was done later to give the setting material something to affect to.
  7. Jdavis37

    Jdavis37 New Member

    Messages:
    29
    Location:
    NC
    John,

    Given I am not a construction person, I can be very slow at times! But, assuming I am reading what you wrote correctly, in simple terms, it sounds like a sheet of plywood type material placed over the deck frame and tub would work. I had wondered what one did with the plywood edge which would otherwise be visible but in your example you had a chrome "Schluter Profile" to hide the wood/cement board. I have not looked yet but assuming I can find a material that will match what we are doing 9something either compatible with our granite or an oil rubbed bronze color profile) this may well do what I need for it to do. It certainly answers the where does the support for the granite come from part without having to tear the existing frame apart.

    I had earlier though about how to support the tub from underneath its ends but going this route eliminates that idea. It could work. I would have preferred having more wood to support the granite but given my dimensional room issues this approach may be a great solution, assuming I am understanding correctly. Am sure my contractor will again love me :)
  8. Jdavis37

    Jdavis37 New Member

    Messages:
    29
    Location:
    NC
    Also, for anyone else reading, our tub will be an under mount tub and not a drop in. What started this was the relative lack of wide wood on top of the tub deck to support the granite that will go over the tub.
  9. Jdavis37

    Jdavis37 New Member

    Messages:
    29
    Location:
    NC
  10. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

    Messages:
    4,690
    Location:
    North Vancouver, BC
    Can you send me a picture of your room and the tub? Maybe the spec sheet on the model you have.

    Let's take a look.

    You need a finished plan before building anything.

    Are you using wood paneling in front? Do you have the tub filler hardware already?
  11. Jdavis37

    Jdavis37 New Member

    Messages:
    29
    Location:
    NC
    THe tub is Kallista Small Perfect Tub and also am attaching a photo of the not quite complete deck. The deck opening etc are all fine with regard to the tub. My concern and most likely lack of understanding is with regard to how the granite slab(s) will be supported given how narrow the wood pieces are on three sides of deck. I have seen photos of similar setups complete so apparently it can be done.

    The faucet is Kohler Devonshire. Regarding tile or wood on front, originally it was going to be wood but now it could be either. Have tonight to make my 49% of the vote for the final decision! I would prefer a wood panel with access but do have some concerns with water. Tile we have selected for shower (which is adjacent to the tub deck) I am not sure I like around the deck. Again I have at most 49% of the vote!

    Question for now is do I need to insist deck be ripped out and have a wider top piece of wood for the window side? The 2 x 3's in usage on the ends will be difficultto rip out due to shower width and toilet bay width. Meaning if I go with wider wood on ends my shower bay will get very small. Presently as laid out it is 43 inches by 53 inches.

    In the photo of room, (a) the picture window is being removed and rpelaced with a smaller window and (b) the toilet bay is where the blue ladder is on left and shower bay is to right of the tub deck.

    For me this goes back to is it possible to do a granite surround using this deck. I may simply be too involved in the process given I am paying a contractor but is my nature to try and understand things. PLus if granite is not installed properly it will be a disaster down the road! Thx again and hope photos help.

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  12. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

    Messages:
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    Location:
    North Vancouver, BC
    OK.

    You have a lot going on here. Who is building this for you? Are they a contractor or a "Handy Andy".

    Why do you not have your insulation and vapour barrier in place on that exterior wall?

    The short ends of the framing is weak. Missing at least one stud.

    The exterior wall framing looks poor as well. I would want to see some more 2"x4"'s transffering the weight down to the sub floor.

    I hate the wood curb. I'd switch this to cement or bricks if it was me or I would be loading it up with a wack of 5" screws pinning all pieces together and to the sub floor.

    Can you dry fit the tub in position and check the plumbing. Sometimes we need to cut the tub a bit to make it fit where you want.

    Also make some pieces to represent the granite out of plywood. Make them exactly the size you want. Lay these over the tub and see what issues arise. This visual perspective will help you see holes in the design.

    The top looks good with the cross hatched 2" x material but I would be adding a 1/4" layer of cement board over this. Setting the granite over your tub is as good as the strength of the tub. It is for this reason we pack it with mortar and make it rock solid - Before installing.

    Dry fit that tub. Make the granite mock ups and repost some pictures. Bust out your plumbing fixtures - we need to see how this will work as well.

    Make sure that the exterior wall is properly insulated and vapour barrier'd before affixing the tub support framing to it.
  13. Jdavis37

    Jdavis37 New Member

    Messages:
    29
    Location:
    NC
    John,

    Thx... I should have added in the picture note things were still a work in progress. The plumbing is being done as I am typing this. As far as the exterior wall, vapor barriers, etc that should (I'll verify) be done as things progress. There will be cement board installed on top of the deck board.

    The contractor is also a licensed contractor and not a handy man. That said, I know we all have strengths and other areas of less than "strength". We discussed deck this morning with granite person as well and in end I asked for the back side to be more substantial. Tomorrow I'll discuss the added framing support for the ends.

    My next question is about packing tub with mortar, something I have a feeling my contractor won't be knowledgeable about 9I could be wrong on this assumption). I know Kallista provided several alternatives in setting the tub, 2 of which do not include a bed of mortar in bottom (they specifically say ensure not letting mortor get under the tub's feet). What exactly do you fill with mortar? Under the tub or up the sides? It would seem to me getting support under the tub lip and into the hollow area of said lip would make the tub edges very firm, certainly firm enough to not flex under granite ( I am less concerned about the weight than I am the flex).

    As the framing gets finished, plumbing in, etc and exterior wall finished i'll send out photos. I am at least feeling better about the top board width as we are making the exterior wall top width an extra 1.5 inches. I'll have the 5l.5 inches from the 2 x 6 on front edge and 4 inches on the exterior wall edge. I also like idea of cutting out plywood templates for the granite to see how things fit. Thx again John

  14. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

    Messages:
    4,690
    Location:
    North Vancouver, BC
    Did you look at the pictures in the photo album I linked you too? It shows some mortar mix in the middle below the tub - covered with light weight poly.

    The feet do not get covered and the mortar supports the middle section.

    The extra mortar under the top of the tubs lip is something I'm sure your contractor has never seen. We just started this practice last Christmas. Still in the proto type testing. The difference is amaZing. This step could be replaced with thin-setting in some rigid foam. gluing in strips of plywood. What ever you can add to increase the strength and decrease the deflection on the tubs top lip - where the granite will be stuck to.


    http://terrylove.com/forums/index.php?threads/framing-for-an-under-mount-tub-installation.51168/
    Last edited: Aug 26, 2014
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