Mold under caulk in shower edges - unavoidable?

We had our bathroom completely redone back in 2018. It's normal to have caulk running over the grout / tiles along the edge where floor meets walls?

In those 5 years, I've taken off the caulk a couple times now to recaulk due to black discoloration under the caulk (that's mold, right?).

I use the GE bathroom silicone with the supposed anti-mold features. It seems to me that the mold is on the wall / grout not on the caulk? A technicality? They say the mold won't grow on the caulk. But it doesnt kill the mold if it's on the wall / grout next to the caulk?

Even though I clean the surfaces, let it dry for days before and after caulking, etc.... water will seep in the grout on the floor to the edge behind the caulk and grow there happliy?

We have a bathroom fan on a timer that runs for 30 minutes when showering.

Am I doing something wrong? I've tried grout sealants. as much as I think 1 said it's good for 10 years, waler beads initially, but within weeks / months, the grout turns dark when taking a shower (the water is getting into the grout?

Any tips if I am doing something wrong here? Or mold / recaulking is a task to do every couple years? The tiles are about 2" x 2".

 

It's likely that you have mold on wet building materials behind the tile, and it's showing up behind your caulking.

 

interesting. Suggestions on how to deal with that? cut a hole in wall in bedroom by that area and see if there's moisture / mold there?

The mold does vary location - last time it was somewhere else in the bathroom.

Is my thinking that the water gets wicked along the grout to behind the caulk and is protected by the caulk way off base / not a possible cause?

 

Anything is possible.

 

Was the shower constructed with a waterproof enclosure or just tile on backer board?

My shower was built in 1986 without a waterproof enclosure. A 2016 renovation revealed disintegration of the wall structure opposite the shower head.


Exterior wall structure in shower disintegrated.

For years before that mold would grow in the silicone caulk joint at the bottom of the tile wall and floor. The copper floor pan prevented leakage below but the wall damage apparently was from water seeping through the tile wall toward the outside.

If you have a waterproof enclosure (Kerdi, etc.) you might just not caulk along the floor joint and leave it open for water to seep out and evaporate.

 

Most current building science recommends a water barrier right behind the tile... so that building materials stay dry and anything moist can dry to the exterior side... anything on the interior side of that barrier dries to the inside.

An example would be Kerdi or Redgard over backer board.

 

they used concrete board on the walls (and floor?) and rubber material on the floor under a concrete material? that the tiles are grouted to.

Seems grout / tile, while lots of decorative options, is more of a pain / more chance for problems vs. a 1 piece shower assembly?

and / or use caulk rather than grout for everything. No cracking (at least less than with grout), no sealing needed, etc.