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Thread: "Precise" rough in of shower? Need advice...

  1. #1
    Electrical Engineer jdf405's Avatar
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    Default "Precise" rough in of shower? Need advice...

    Hello all!

    I'm going to be roughing in a Kohler handshower / slide bar (K-8520) in the next few days. The installation manual can be found at:

    http://www.us.kohler.com/onlinecatalog/pdf/088148_2.pdf

    Page three of the manual shows a 1/2" nipple protruding beyond the finished shower surface 9/16".

    I can make a fairly good estimate of the thickness of the tile wall but it seems that to specify something down to the 1/16th means it is fairly important.

    Without knowing the thickness of the mortar/thinset that precisely how would you rough this in? Once I put the blocking behind the ear'd ell I only have nipple options in 1/2" increments. One can crank down on a brass nipple only so far in good conscience...

    Access from the rear is an option but it will delay the rest of the project significantly (drywall installation in another room would have to wait for finished tile in this bath).

    Any ideas?

    Thanks for the help!
    Jonathan

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Don't use Kohler! They are probably the hardest to install and have look good as you've found out, they require very precise location. If you don't get it exact, the part will either be recessed, stick out, or not seal. Way too much hassle for what it's worth, IMHO. Kohler also changes designs frequently, and getting parts down the road can be a problem. IMHO, they are infected with the 'not invented here' syndrom, and choose to do things their own way, regardless of the consequences. Thus, it is rare that a part stays in 'style' and therefore stock for very long. Their parts catalog looks like a small town phonebook. As a result, few dealers stock parts, so you are at the mercy of the factory, if they still have it or will make it for you.

    If this backs up to an interior wall, it might be easiest to just tear it open and anchor the blocking and the el exactly where you need it after the tile is up. Otherwise, it is going to be a guess, and the consequences of not getting it right will likely bug you forever. You can set the tile around that opening first to set the plane, then fill in the others, but you can't just make the thinset layer thicker on one tile, or it will stick out, or be recessed to give you the projection you need...a major pain.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Electrical Engineer jdf405's Avatar
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    Oh joy. Thanks for the fun weather report

    I installed a couple of Hansgrohe thermobalance valves last year in my other bath and I thought those were a certified P.I.A. For all that $$ they charge they used the cheapest crappiest stainless steel place to screw the escutcheon into and the stainless steel screws kept binding and galling. It took me hours!

    The only nice thing about the Hansgrohe thermobalance is that you get both thermal scald protection AND volume control in one knob. To get that out of Kohler you have to buy another expensive valve and trim.

    So other than "good wishes" do you have pointers on how to best predict the rough in depth? Is there some guidance as to how far a 1/2" nipple will thread into a FPT fitting?

    -Jonathan

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    DIY Junior Member K.'s Avatar
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    1/2" npt threads are rated between .32" hand tight and .534" max thread engagement so there could be some room to manuever there as long as that connection doesn't have to seal against static water pressure when the handshower is off.

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    Electrical Engineer jdf405's Avatar
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    Quote Originally Posted by K. View Post
    1/2" npt threads are rated between .32" hand tight and .534" max thread engagement so there could be some room to manuever there as long as that connection doesn't have to seal against static water pressure when the handshower is off.
    Hmm, very cool. Where is this data from? That would suggest there is almost 1/4" in slop there. Some hope...

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    Moderator & Master Plumber hj's Avatar
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    quote; 1/2" npt threads are rated between .32" hand tight and .534" max thread engagement

    Now what "rocket scientist" engineer came up with those dimensions. The amount of engagement depends on the strength of the installer, and the size of his wrench, along with his amount of determination to not have a leak. I have seen "plumbers" who can barely tighten beyond hand tight, and I have seen others who "bury" the entire thread in the fitting. But for this situation, I would assume the heads have some type of "trim ring" that allows for some deviation. Engineers ALWAYS specify an exact distance, even though that is almost impossible to accomplish in the real world, but they say that's not their problem.

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    Electrical Engineer jdf405's Avatar
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    Quote Originally Posted by hj View Post
    quote; 1/2" npt threads are rated between .32" hand tight and .534" max thread engagement

    ...Engineers ALWAYS specify an exact distance, even though that is almost impossible to accomplish in the real world, but they say that's not their problem.
    HJ, I'd like to know where those came from as well - maybe they did come from an engineering model of the taper on the thread and max. allowable distortion of the metal... or maybe they were "PANOMA"...

    You're right about it depending on the installer & how much coffee he/she had that day, but maybe its relevant for estimating.

    Eitherway, a good engineer will specify an exact (or nominal) distance, but include a tolerance for the real world. What's missing is Kohler should have specified this as" 9/16" +/- 1/8" or whatever tolerance can be taken up by an o-ring etc...

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Default Fixture placement

    Take a piece of cardboard and a piece of your wall tile and this will be very close to the finished measurement of the tile and the mortar.

    You need to see if the wall is Plumb (level) and if it not is this going to be fixed. If your wall falls in at the the top you may build out the top affecting your measurements.

    Have your plumber install the brass rough in with a pex supply and tell him you need an inch of play back and forth. if it is not perfect you can get in there with little shims after the fact and fine tune. Set the rough in at the exact depth and you should be fine.

    Make the plumbers job easier by having 2"x10" stock, some 2"x4" stock and plywood scraps. A skill saw on site and some wood screws.

    What about your tile lay out? I'm guessing you want the layout to match your final fixture placement. It is easier to do your layout from the finished ceiling height rather than from grade or tub deck.

    Good Luck


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    Electrical Engineer jdf405's Avatar
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    I just spoke the folks at Kohler (and called Grohe about a similar setup) and the first person at Kohler said it needs to be exact GASP. Gimme a break. Some academic had their way with +/-0 inch tolerance... Then I got an "installation technician" at Kohler on the phone who said there's really a 1/16 to 1/8 fudge either way on that...

    I'll let you know how it comes out in a few weeks once the tile is up.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Check out www.johnbridge.com. There are lots of people that had troule installing those Kohler parts...you can get their feedback - use the search function.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    One who lurks Basement_Lurker's Avatar
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    I am not a fan of Kholer by any means, but this seems to be a pretty standard installation of a shower ell and a slide bar. The Kohler shower ell doesn't seem to have a gasket behind it, so you are meant to caulk it. Just keep in mind that your shower ell won't sit perfectly flush with the wall, so you have about an 1/8 to 1/4 inch gap tolerance that you can reasonably hide with a bead of caulk.

    My advice to you is to measure, measure, measure! If the nipple is too short, you won't get a good seal for the drop ell. If the nipple is too long, you will have an ugly gap.
    Broken promises don't upset me. I just think, why did they believe me? -Jack Handy


    www.blackbirdkitchenandbath.com

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    DIY Junior Member K.'s Avatar
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    Hehehe, I'm not a plumber either so on this forum I'm no expert, but I do think the thread engagement spec is handy to have. There's a few different types of tapered threads out there and amongst other things they all have engagement specs. For me as a diy'er, it was the only way to get a sense of how many turns to apply and when to give up with the wrench and redo the teflon wrap to fix a leak. With a handshower ell or shower arm you install it in units of complete turns so you definitely want to know where you are. I've also needed to know thread engagement at my real job (not a rocket scientist!) when trying to figure out positioning for a thermometer/thermowell combo (2 sets of threads there). I recognize that any experienced home-owners or plumbers probably have a good intuitive feel for pipe threads though and don't need the numbers specifically. Cheers!

    -Jonathan

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