Use of 1/4 inch Hardie backer board on tub surround

Discussion in 'Shower & Bathtub Forum & Blog' started by nickhnw, Feb 1, 2011.

  1. nickhnw

    nickhnw New Member

    Messages:
    3
    Location:
    Kirkland, WA
    Greetings,

    I am in the middle of a project to replace an old fiberglass shower with a bathtub in a typical alcove installation. The new rough plumbing has been signed off by the building inspector and the tub is in place. As per the instructions from the Kohler bathtub I attached 1/4" furring strips to the studs and then covered the walls with plastic sheeting, overhanging the tub flange. With the furring strips in place the Hardie backer board will overhang the tub flange as it should. I attached 1/2" backer board to the rear wall of the alcove but I am balking at the side walls. This is because the drywall in the rest of the bathroom is 1/2" and if I put 1/2" backer board over the 1/4" furring strips on the side walls it will be 1/4inch higher than the drywall it butts upon against. The bullnose for this tile is flat so I can't hide the gap that way. Using a 1/4" caulk seam to hide it would probably look tacky because it would be along the very visible edge of the bullnose. So, my thought is to use 1/4" backer board on the side walls, which will make the finished height 1/2" to match up with the drywall. The FAQ section of the James Hardie website states that it is fine to use their 1/4" product on a shower wall. I guess what I'm looking for is some confirmation from those with real world experience that this will be ok.

    Regards,
    Nick
  2. jadziedzic

    jadziedzic Member

    Messages:
    96
    Location:
    New Hampshire
    1/4 inch is way too flexible for a wall - if someone leans against it, which isn't all that unusual, you stand a good chance of cracking thin set, tiles, grout, or all of the above. You can machine HardieBacker fairly easily; use a router with LOTS of ventilation and cut a 1/4 inch dado along the wall side of the bottom edge where it will overlap the tub flange, and skip the furring strips on the side walls. By the way, the HardieBacker 500 is actually about 7/16th inch thick, so you'll still have a transition to deal with.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,188
    Location:
    New England
    James Hardie approves it for wall use...most pros won't use it that way, they prefer the thicker stuff - it gives them more leaway. Another way to achieve what you want (may not be possible now without a lot of work), is to notch the studs, rather than using shims...still get things even, but your thickness issue goes away. Putting in some more blocking or studs to shorten the span, and it should be okay (well, they say it already is!).
  4. nickhnw

    nickhnw New Member

    Messages:
    3
    Location:
    Kirkland, WA
    Thanks very much for the advice; the suggestion about cutting a dado at the bottom of a 1/2" sheet makes good sense. I'll take the furring strips off the side walls and do just that.

    Regards,
    Nick
  5. johnfrwhipple

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

    Messages:
    4,553
    Location:
    North Vancouver, BC
    Hardi Board Installation instructions (PDF's)

    Post(s) deleted by John Whipple
    Last edited: Mar 18, 2014
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,188
    Location:
    New England
    In the James Hardie FAQ section, they say you can use it in a shower, but they recommend the thicker stuff because it is easier to match up with the drywall. If you could put in some additional blocking to shorten the span, it won't be an issue. The silica dust is toxic, doing this outside with the proper mask is crucial. Routing it (or even sawing it rather than score and snap) can release a lot of dust, and special precautions must be used.
  7. nickhnw

    nickhnw New Member

    Messages:
    3
    Location:
    Kirkland, WA
    Thanks for the opinions and options, I appreciate them. I cut the dado using my Makita hand-held tile wet saw; basically a small circular saw Makita used to make (maybe still does) with a water bottle attached. I did three passes side-by-side and chiseled it. It only took a few minutes and there was no hazardous dust to contend with.

    Nick
  8. johnfrwhipple

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

    Messages:
    4,553
    Location:
    North Vancouver, BC
    Nice work Soldier!

    Post(s) deleted by John Whipple
    Last edited: Mar 18, 2014
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