Cutting a Square Hole in Fiberglass Shower Surround

Discussion in 'Shower & Bathtub Forum & Blog' started by BobL22, Jul 23, 2017.

  1. BobL22

    BobL22 New Member

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    Jul 23, 2017
    Location:
    Connecticut
    Hi, newly registered to the forum, but I've visited a lot for help and insight in the past. I've searched the site, but couldn't find an answer to this question. I'm installing a Brizo (Delta) shower valve and trim in my shower surround. I've used a hole saw in the past for installing round valves, etc., however, this trim package is rectangular, and I actually have to trace around the rectangular body (to cut the surround) so that it is slightly recessed into the surround wall. Understanding the criticality of getting this right, what is the proper tool/method to accomplish this? Thanks in advance for the help.
     
  2. Reach4

    Reach4 Well-Known Member

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    Sep 25, 2013
    Location:
    IL
    I have no knowledge of that trim. For cutting rectangular holes where the cut needs to be good, but does not need to be perfect, I use a jigsaw with a metal cutting blade, maybe 24 TPI. It cuts slower than a courser blade. I use the orbital feature to speed things up if needed.

    If the trim does not actually cover the cut edge, I would not try such a cut. If you think the edge is going to show, I suspect you want to re-read; that does not seem right. I am not a pro.
     
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    New England
    Fiberglass does not like square cornered holes...it puts a fair amount of stress on the materials, and is more likely to crack. So, I suggest that you draw out where you want the hole, then use a drill bit on the corners to actually make them a curve, then, you can cut the lines connecting them. Depending on how the thing is made, a saber saw might put a lot of stress on it and crack things. Some of those panels can be cut just by using a utility knife with a new (sharp) blade. Does the instruction set give any indications? Maybe a call to the manufacturer would be a good idea.

    As to how to measure and mark...first thing I think you'll need to do is to verify that the floor is level and flat, then, that your studs are plumb, otherwise, the angles involved will make it very difficult to precisely locate your desired hole.

    Many valves have what is called a thin-wall installation method. This often requires the actual hole in the wall to be smaller than the plaster guard/frame of the mounting box. They use that guard flush up against the back of the panel, then, screw the trim down, sandwiching the two together and clamping the wall in between them...otherwise, the flexible panel would not be able to be sealed. In that case, the hole must be smaller than the frame, and a round hole might just work fine, but maybe with some slots or holes for the trim's screws to get to the valve. Double-check the instructions to see if it has a thin-wall installation method.
     
  5. Master Plumber Mark

    Master Plumber Mark Master Plumber

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    your hole does not have to be perfect, it only has to be about a 1/2 inche smaller the the face plate trim that
    will be showing on the fiberglass.....

    Use the finish face plate to mark the outline on the fiberglass with a pencil
    go inwards about 1/2 inch and proceed cutting it out
     
  6. BobL22

    BobL22 New Member

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    Connecticut
    Thanks. Admittedly, the instructions are a bit vague - they start by stating "...if this is not a thin wall installation...", but they never return to a thin wall install. Then they forward you to the specific instructions directing you to remove the plaster guard, which is where the confusion came in. Since I am installing over bare studs, I believe I should be following thin wall install, which don't exist.
     
  7. BobL22

    BobL22 New Member

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    Thanks for the input. You have me wondering if, after I install the anti-rotation pins, whether I even need the mounting brackets. It seems to me that for a thin wall application, they're not really adding anything to the integrity of the trim assembly. For reference, I'm installing the Siderna T60280. It seems that the mounting brackets are only useful if you are recessing them into a "thick wall" installation.

    Again, all input is appreciated. Thanks.
     
  8. BobL22

    BobL22 New Member

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    Yeah - I've read it six times now. I'm not a pro either, so the instruction, while clear to some, have me a little baffled. Thanks for the help.
     
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
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    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Mount the valve so that the plaster guard is even with the back of the shower surround, cut a hole big enough to ensure that guard's edges are entirely on the back of the opening, and not likely to slip into the opening. Double check that the trim will fit and tighten down on the thing. If the valve is mounted rigidly, that will keep the surround's wall from making a big opening if you lean on the wall. It might require shorter screws for the trim to fit. Mock it up to verify it will work like that. The company may have thin-wall instructions on the website, or will send you some if you call. Normally, they're included.
     
  10. BobL22

    BobL22 New Member

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    Got it - Thanks. I did check the website, and there's nothing more than what was included with the trim pack. I think what was confusing me was the instruction to trace the outside, re-cut, and recess the bracket. Thanks again.
     
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