Question about making a mortar bed under a tub

Discussion in 'Showers and Tubs' started by Zanne, Feb 11, 2020.

Help Support Plumbing Forums by donating:

  1. Feb 11, 2020 #1

    Zanne

    Zanne

    Zanne

    Well-Known Member

    Joined:
    Mar 23, 2013
    Messages:
    1,804
    Likes Received:
    199
    Location:
    ,
    I'm helping my friend with fixing up his house & he wants to switch from a small shower stall to a shower/tub unit. He wants this American Standard Saver tub https://www.lowes.com/pd/American-S...-Acrylic-Rectangular-Right-Hand-Drain/3394192 with it's matching surround.

    The instructions say to use a mortar bed underneath (although I'm still waiting to hear from the mfr on how much of a gap there is between the floor & the tub's bottom to know how high it needs to be.

    I've seen all sorts of different suggestions and opinions on what to use for the mortar bed, what to put under it, what consistency to make it (some say barely wet, others say wetter, etc), and whether or not to put a plastic barrier between the tub & the mortar bed.

    I saw the spray foam suggestion but I've seen how spray foam does longterm & it is not a good idea, IMO. Someone suggested the Sika expanding foam that hardens like concrete, but my concern would be it could expand too much. I've seen some people suggest thinset material for mortar and others suggest "drywall mud".

    So, some questions:
    1. What sort of mortar is the easiest to work with that would yield the best results? Would drywall mud work?
    2. What is the best mixing method?
    3. How high does the mortar bed need to be? (mfr recommended two 80lb bags of concrete)
    4. Can we use roofing felt under the mortar bed?
    5. Should we use some sort of plastic sheet or thin barrier/coating on top of the mortar bed to prevent it from clinging to the tub in case the tub needs to be pulled for a repair?
    6. For the drain, if the mfr says not to use putty (to use silicone instead), do we still need caulk if we get a caulkless drain (similar to the EZ-Flow shower drain Frodo showed in another thread)?
    7. What parts would we need to do a direct connect drain (with trap below the tub's drain instead of below the overflow)? I know we'd need some sort of 1-1/2" straight piece that is threaded on the inside. I saw one from Westbrass. I know we will need the overflow shoe (or what is that piece called?), gasket, plate, etc. We'll need the pipe to go down from the overflow and a sweep to carry it to a sanitary tee for the drain and then the P-trap. I think there needs to be a tub gasket between the drain and the bottom of the tub and we'll need the part that screws in to the threads from the top.

    Any help would be appreciated. Pictures are welcome since they help me visualize better.
     
  2. Feb 11, 2020 #2

    CT18

    CT18

    CT18

    Junior Member

    Joined:
    Apr 30, 2014
    Messages:
    581
    Likes Received:
    144
    Location:
    Bloomfield Hills, Michigan
    We used to just grab some mortar from the masons and plop it down before we set the tubs and then squish it down with the tub. If you go expanding foam make sure you put some screws or nails around the drywall lip of the tub to keep it from rising up.
     
    Zanne likes this.
  3. Feb 12, 2020 #3

    Zanne

    Zanne

    Zanne

    Well-Known Member

    Joined:
    Mar 23, 2013
    Messages:
    1,804
    Likes Received:
    199
    Location:
    ,
    CT18, we've ruled out expanding foam due to the logistics. There will be an acrylic tub surround & no drywall. He might just put some sort of molding to cover the top flange of the wall set.
    There are no masons in this area so I don't even know where the type of mortar used on bricks is purchased (likely one of the big box stores an hour away though).
     
  4. Feb 12, 2020 #4

    CT18

    CT18

    CT18

    Junior Member

    Joined:
    Apr 30, 2014
    Messages:
    581
    Likes Received:
    144
    Location:
    Bloomfield Hills, Michigan
    You could always just mix up some quikcrete and dump it down and then set the tub. We would just hop in it to spread it out underneath. I am not saying what we did was the correct way, we didnt put much thought into it.
     
    Zanne likes this.
  5. Feb 13, 2020 #5

    Jeff Handy

    Jeff Handy

    Jeff Handy

    Pro Handyman, NOT A Pro Plumber

    Joined:
    Jul 5, 2019
    Messages:
    1,315
    Likes Received:
    219
    Location:
    Chicago suburbs
    Don’t set into any mortar or whatever until it is shimmed or supported by framing to be the correct level all around.

    Shims should be fastened so they don’t scoot around.

    Obviously you want a mortar mix, not any kind of concrete mix, you don’t want any rocks or big aggregate, just sand and cement and maybe additives for flexibility.

    But pros would know better, hopefully some will jump in here.
     
    Zanne likes this.
  6. Feb 13, 2020 #6

    Zanne

    Zanne

    Zanne

    Well-Known Member

    Joined:
    Mar 23, 2013
    Messages:
    1,804
    Likes Received:
    199
    Location:
    ,
    Thanks, Jeff. The plan is to hang the ledgerboard and stringers, set the tub in as a dry test-fit to make sure everything lines up and that it is level, then pull it and do the mortar bed & make sure it is up to the height of the bottom of the tub. I'm still trying to figure out the best mix to use & whether to have it wet & peanutbutter consistency or have it like brown sugar where it is damp but not overly wet like some videos show.
     
  7. Feb 14, 2020 #7

    Helper Dave

    Helper Dave

    Helper Dave

    Member

    Joined:
    Oct 12, 2019
    Messages:
    10
    Likes Received:
    4
    Location:
    Wisconsin
    We use a basic, non-structural mortar. Nothing fancy. It does the trick.

    The keys to mixing it are that you're looking for it to be grainy and fairly thick. The peanut butter texture is too wet too support anything. You don't want it clumpy, on the other hand. It needs to be consistent to set correctly.

    In a five gallon bucket, start off with just 1 1/2" or so of water, so you don't get dry clumps at the bottom. Add a bit of powder, mix, splash on water as needed, and keep adding mortar, then water until you've got the quantity you need.

    And a little water goes a long way with mortar. Even too vigorous a splash can be too much, and throw the balance off.

    Took me a bit to get the hang of making it when I started, but hopefully my tips help.
     
    Zanne and Jeff Handy like this.
  8. Feb 14, 2020 #8

    Zanne

    Zanne

    Zanne

    Well-Known Member

    Joined:
    Mar 23, 2013
    Messages:
    1,804
    Likes Received:
    199
    Location:
    ,
    Thank you very much, Dave! You lived up to the "Helper" part of your name. I will pass the info along to my friend as he will be mixing the mortar.
     
  9. Feb 22, 2020 at 10:16 PM #9

    Zanne

    Zanne

    Zanne

    Well-Known Member

    Joined:
    Mar 23, 2013
    Messages:
    1,804
    Likes Received:
    199
    Location:
    ,
    Has anyone here tried the mortar technique of putting down 9 piles of mortar (high enough that they will all be squished and spread out) under a tub? I saw it mentioned in this article https://homeguides.sfgate.com/kind-mortar-use-under-bathtub-97453.html and some people on another forum were suggesting it, but I wanted feedback on whether or not it's a good thing.
     
  10. Feb 23, 2020 at 1:32 PM #10

    wood4d

    wood4d

    wood4d

    Well-Known Member

    Joined:
    Apr 1, 2014
    Messages:
    159
    Likes Received:
    32
    Location:
    ,
    we use structolite under tubs and showerpans. you can set 3 tubs with one bag.
     
    Zanne likes this.
  11. Feb 24, 2020 at 4:47 AM #11

    Zanne

    Zanne

    Zanne

    Well-Known Member

    Joined:
    Mar 23, 2013
    Messages:
    1,804
    Likes Received:
    199
    Location:
    ,
    Hmm.. I've never heard of structolite. I'll have to look it up and see if it's available. Only need to set 1 tub currently.
     

Draft saved Draft deleted

Share This Page

Group Builder