The grout in my shower is cracking and I hear hollow sounds under the tiles, so I've been researching for a DIY fix. After listening to what the experts have to say, I've realized Korean bathroom construction is just hopeless.

Everything has to be done fast and cheap, so they're basically building ticking time bombs that just need to last long enough to avoid immediate complaints. If you have a lifestyle where you're spraying water on tiles, you need a dual drainage system so that water seeping under the tiles can actually drain out. But whether it's a brand new apartment or a top-tier remodeling firm, nobody does dual drainage work, and the materials for it are rare. You can basically assume no one does it. Everyone just pretends the top layer of tile and grout is a perfect waterproof seal and only builds for water to drain from the surface. When water inevitably seeps through the grout, it either gets absorbed by the cement, luckily evaporates, or just pools there and rots... it's a total gamble. For a regular person, there's zero way to change this. Maybe if you're building a house from scratch and pay extra to convince the contractor? Otherwise, there's no answer. It's just a system where you use it until it breaks, remodel it, repeat, and then eventually the whole building gets reconstructed. I've realized that a tiled shower floor is just as reckless as a masonry tub. The tile+grout system will 100% leak. The best choice for a regular person is to either install a one-piece FRP shower booth or just stick to a tub and shower curtain for peace of mind.