Can I waterproof a bathroom floor without removing the existing tile?

In most cases, no — you cannot effectively waterproof a bathroom floor without removing the existing tile. Proper waterproofing requires a continuous membrane applied directly to the substrate (the subfloor or cement board), and that membrane needs to be installed beneath the tile, not on top of it. Applying a topical sealer or coating over existing tile is a temporary cosmetic fix, not a waterproofing solution.

The reason is straightforward: waterproofing works by creating a continuous, bonded barrier between the tile assembly and the structural subfloor. Products like Schluter Kerdi membrane, RedGard liquid-applied membrane, or Laticrete Hydro Ban are designed to bond to cement board, plywood, or concrete — not to glazed tile surfaces. Even if you could get a membrane to adhere to old tile, you'd still have the original tile layer trapping any existing moisture against the subfloor, potentially causing hidden rot and mould growth.

When the Tile Must Come Up

If your bathroom floor is showing signs of water damage — soft spots, cracked grout lines that keep reappearing, tiles that rock or feel hollow, musty odours, or visible staining on the ceiling below — the tile needs to come out so the subfloor can be inspected and repaired before any new waterproofing is installed. This is especially critical in GTA homes built between 1945 and 1970, where original bathroom floors may have decades of slow moisture infiltration around toilet flanges and tub edges.

The Ontario Building Code requires waterproofing in all wet areas, and the only code-compliant approach is a proper membrane system installed on a sound substrate before tile installation. In Toronto, this work should be done by a professional tile installer or bathroom renovation contractor who understands the layered system: subfloor inspection and repair → cement board or suitable backer → waterproof membrane → thinset → tile → grout → sealant.

The One Partial Exception

The only scenario where you might address floor moisture without full tile removal is applying a penetrating grout sealer to existing grout lines as a maintenance measure in a bathroom that has no underlying damage. This won't waterproof the floor, but it reduces water penetration through grout joints and extends the life of the existing installation. Quality grout sealers cost $15–$30 and should be reapplied annually. This is a reasonable DIY maintenance task.

For a proper bathroom floor waterproofing as part of a renovation, expect to pay $1,500–$3,500 for demolition of existing tile, subfloor inspection and repair, waterproof membrane installation, and new tile — for a standard 40–50 square foot GTA bathroom floor. It's not cheap, but it's far less expensive than repairing water damage to floor joists and the ceiling below, which can run $5,000–$15,000 if structural repair is needed.

If you suspect moisture problems under your bathroom floor, get a professional assessment before deciding on your approach. Toronto Bath Remodeling can connect you with experienced bathroom renovation contractors through the Toronto Construction Network who can evaluate your situation and provide a proper quote.