Old bathrooms rarely have straight walls or level floors. When tiles are removed, you often discover bumps, hollows, or slanted areas. If these are not corrected before new tiles are installed, the final result will look crooked and water will not drain properly.
A good contractor will first re-screed or re-plaster to correct levels. This adds time and cost, but it prevents water from pooling in corners or flowing out of the shower area. Proper leveling also helps glass doors close correctly. Renovation isn’t just about replacing what you see — it’s about fixing the structure underneath so the new bathroom actually functions well.