Fiberglass pan install - creaking sound

[MikeCO]

Yesterday, I installed a fiberglass shower pan following the manufacturer's (Vigo) instructions which included laying mortar underneath, fastening the flange to the studs, and shimming between the flange and the stud if it is not square. After 24 hours, there is a very slight creaking when you step around the pan which seems to be due to the connection at the flange where it rubs with the wood. I was debating whether to use screws or nails and ended up using roofing nails so the head would lay flat - I saw conflicting opinions between pan head screws, deck screws, roofing nails, and not fastening at all for prefab shower pans.

As you can see from the pictures, I needed to shim at almost all the studs, and one of the shims has split. Is there anything that you would recommend changing or adding at this point to minimize creaking now or in the future, or is this just expected when you have a prefab pan? Honestly with the shower water on, it's hard to imagine hearing the sound but want to make sure it's done correctly as well!

 

[Jadnashua]

First, I'd prefer SS screws versus galvanized nails. Depending on how thick the wall of the receptor is, you might be able to use flathead ones after using a countersink bit so the head was flush. While it may take a long time, the nails will start to rust eventually, potentially staining the tile, or in a severe situation, since rust is bigger than the elemental metal, push the tile away.

Creaking implies movement and it won't get better.

What did you put underneath, and how did you apply it? Were you able to make sure that the rim of the pan is perfectly level when setting it? That's important, and that's one reason why they suggest mortar underneath. The second reason is to better support the pan so it doesn't deflect when you are standing in it, which, is probably why it's creaking...there's movement, potentially pulling the edge away from the wall.

The wetter you make the mortar, the more it can shrink. It can also help if you apply some roofing felt or plastic on the floor first, and that will prevent it from drying out quickly, and making it weaker. Cement in the mortar literally incorporates the water into the chemical structure...what's not needed, will eventually dry out, but drying is not the same as curing. Cement is stronger when it has the design amount of water. Too much, and it can microscopically hold the cement grains and sand apart, making it weaker since they won't interlock as much. Cement cures as it literally grows into crystalline spikes, interlocking like a bad hair tangle. The water starts that growth off.

 

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[MikeCO]

We put Quikrete mortar mix underneath it and ensured that the pan was level (see below picture). We tried to err on the side of drier like wet packed sand, so I'm hoping it wasn't too wet. I did not put anything underneath the floor first.

At this point given that it's in there, would you recommend making any changes either with the screws or mortar?? Pulling out the nails and replacing with screws would probably be doable if I am careful, redoing the mortar would be not ideal.

 

[Jadnashua]

It's almost impossible to get mortar flat when applied directly, then setting the pan on top since the pan itself may not be flat OR the same thickness all over. What you need to do is to place a bunch of piles then smush the pan in place so that it can get into any ridges, high/low, etc. points to provide support and end up level, too. Not sure if you'll ever get all of the creak out of it unless you pull it up and start over. It may be easier to try some screws. If the tiling flange is thick enough, I'd consider countersinking the hole so it will end up flat when the screw is installed, and use SS ones.

 

[MikeCO]

Thanks, I ended up pulling out the nails and replacing with SS pan head screws which fixed the creaking. The flange is pretty thin so I didn’t want to try countersinking.

The nails came out way too easily, and the creak was coming from where the flange rubbed against the wood. It is very solid now - the mortar underneath has pretty good coverage across. I know it looks flat but it was raised higher than needed and then smushed the pan into position. Good tip on the piles and that would’ve been simpler, now that the creak is fixed I feel comfortable calling it good.