Gelcoat Shows Wave-Like Discoloration - Why?

This is actually about a fiberglass pool. You guys seem to be the experts at gelcoated fiberglass that has been cut or gelcoat ripped away exposing the glass underneath - information on this on a fiberglass pool is nearly non-existent. Thank you for any insight your can share...

Short-Version of what's transpired to date...
- fiberglass pool shell & tanning ledge shell cut down the side by ~6.5" for a length of ~13.5' to create an underwater transition between the two
- concrete poured in between to bridge the gap and connect the ledge and pool
- thin layer of roll-on waterproofing applied followed by epoxy mortar, glass tile and grout
- chips in the gelcoat where they cut exposing the fiberglass underneath were still exposed and mushy when small amount of pressure applied, no repair done to gelcoat - eventually covered with a bullnose tile
- leak developed along the tile/grout line where the underlying seam between fiberglass and concrete meet and along the vertical edges (leak went on for 2 years before it could be located, worse when its cold)
- no bubbling/blistering, if rub gelcoat above and slightly below waterline, you do get a little blue on your fingers.
- these wave-like discolorations have developed in/on the gelcoat - What is it?

Long Version:
Pool installed in 2022. In an attempt to merge a fiberglass pool and fiberglass tanning ledge where the connection would be underwater, pool builder/installer cut down the side of the pool around 6.5" for a length of approx 13.5'. He then poured concrete over the gravel backfill between the ledge and the pool, smoothed it out across the top even with the height of the cut edges. Then a thin coat of waterproofing went on. Followed by what he claims is epoxy based mortar, glass tile, and expoxy based grout. The vertical cut sides of the pool got a little concrete and a little waterproofing (2" or less up the surface) followed by mortar, tile, grout. The edges where the finished gelcoat and the cut gelcoat meet had many decent sized chips along them. Pool builder said the chips in the gelcoat did not need to be repaired in any way it was fine and the bullnose tile would cover it despite the exposed fiberglass being "mushy" to the touch when a little pressure applied.

Fast forward and there is a leak that no one could find for 2 years (lose 2-4" of water in 8 hours primarily when its cold) - it was along the first row of tile on each side that was covering the seam where fiberglass meets concrete. Temporary fix was to silicone grout over what was there until we could figure out next steps to fixing this. In the meantime, pool continued to lose water (up to 1/2" over 10 hours) but couldn't identify leak until yesterday during "demo"..the tile running vertically wasn't waterproofed all the way initially, the silicone grout temporary fix did not extend up the vertical part. There was foam insulation of some type in behind there and it was soaking wet - press on it and water just flowed out. The little bit of concrete in there was wet.

Now here we are and we also have these wave like discolorations along the side of the pool that the cut is on primarily and has started to come across the short sides of the pool to the opposite side. There is no bubbling or blistering of the gelcoat. If you rub the gelcoat with your fingertips with a little pressure (at least above and just below the waterline) you do get a little blue on your fingers.

Any idea what is going on and would cause this? Could this be related to the water getting in behind there with the leak or the process used in joining the tanning ledge and pool together after cutting the fiberglass pool shell exposing internal fiberglass fibers? And/or the exposed fiberglass from the chipping of the gelcoat leaving the glass exposed?

There is nothing like this in the pool forums that I could find...then again, not many people have had their fiberglass pool shell cut either. Hoping someone out there can shed some light on this and/or have seen this before.

 

I didn't read everything.

If the gel coat sags while being applied the pigments can shift and separate in odds ways, its not uncommon. As the surface chalks, which is what's happening when you get color on your fingers, it exposes that separation under the surface.

 

Thank you

 

Can’t tell you what I’m looking at in the photo?
Is the surface supposed to look scabby?
The fiberglass/concrete joint sounds entirely wrong, and will inevitably leak.
The fiberglass side should have been keyed into the concrete, for structural as well as waterproofing integrity.
Now you’ve got a mess, and it’s going to be destructive to repair it.
I’d cut the concrete back from the edge of the fiberglass enough to fully clean both surfaces and insert a backer rod followed by a high quality sealant to form a flexible joint.
I’d stick down the bullnose tile in the sealant, and then grout the joint with a flexible tile grout.
The alternative would be to glass over the concrete, with a generous lap over the edge of the pool side.
Your contractor and his engineer should know how to do this, and should be held responsible!

 

We’ve got someone taking care of the repair now, thankfully. What I’m asking about is the wavy discoloration on the pool sides. It reminds me of a water stain on fabric