Glueing PVC to Vikrell tub surround -- right adhesive/glue?

[Thegeographer]

My unique situation -- our bathroom has a small window in the back corner of the tub/shower area. When I remodeled, I didn't want to lose it, so I cut a 20"x20" notch out of the Sterling Vikrell tub surround I used. And, installed a new window. Now, I need to trim around the window so that the whole thing is waterproof. I found some exterior PVC corner trim that's large enough (3 1/2 inches on each side of the corner) to cut down to size and make a non-porous frame around the window. Now, the tricky part -- I need to glue it in place. The way the Vikrell surround works (with a lattice of bracing on the back), I can't trim nail the PVC into place. The glue/adhesive is going to have to hold the whole thing in place.

I bought two types of tub surround glue (Loctite Power Grab Tub Surround and Loctite PL 550) and did a test glue up -- gluing extra PVC pieces to themselves. After waiting two days to test, neither held well and the PL 550 hadn't fully cured. Reading the fine print on both adhesives, they say "not recommended for overlaps on multi-piece units" and that "one surface should be porous." So, I think I have the wrong tool/glue for the job.

What recommendations do you have for glueing this PVC trim to Vikrell that'll hold?

Thanks,

Eric

 

[Thegeographer]

I did call Kohler/Sterling to ask their advice, and they said that any adhesive may stain or discolor the Vikrell and to only use 100% silicon sealant. Also found out (too late) that they sell a window trim kit: https://www.sterlingplumbing.com/product-detail/va-80172?skuid=VA-80172

So, same question: any recommendations? Is 100% silicon caulk going to be strong enough to hold this in place?

 

[Sponsor]

 

[Terry]

I think I would also go with Silicone for those parts. Clear is always my first choice.

 

[Tuttles Revenge]

Seems like you could glue on some wood to the backside of the surround walls to add more surface area for the trim you're installing. Guess it depends on how much space is behind the void of the surround to your studs.

We install a few of the Sterling surrounds, good find on the OEM trim kits.

Silicone is a strong adhesive. That is what we use to finish the seams.

 

[Jeff H Young]

Definitely put backing in as noted in step 1 . never seen that kit that looks handy

 

[Thegeographer]

Thanks all. I'll try to figure out something to use for backing (rigid foam?) that I can get in that space and go with the silicon caulk for adhesive and sealant.

I'm also trying a fancy cut on the PVC trim to get a slight pitch on the bottom piece of the frame. Getting some drainage will likely minimize problems down the line.

 

[Thegeographer]

Here's a pic of the finished window frame. PVC framing on the bottom and wood on top. Had to bevel the PVC on the right to account for curve of the shower insert (PITA). I also used purple foam as backer for the bottom piece to create more structural support.

I did test the strength of silicone caulk as compared to the tub surround glue on some PVC scraps. I could pry apart the tub surround glue with my fingers and one of the glues hadn't fully cured after 72 hours of drying. With silicone caulk, I had to use a screwdriver to pry the pieces apart (after 48 hours, fully cured). Much, much stronger.

Way too much time for one window frame...

Thanks again for the help!