Hi @LorenClayton,
From what you have described, the mixed advice you are receiving is understandable because diagnosing shower leaks is not always straightforward, and different trades approach the problem from different angles. A moisture meter reading of ninety nine percent on the bathroom floor simply tells you that moisture is present in the substrate, but it does not confirm whether the source is failed grout, failed waterproofing, or water that has migrated through the tile bed over time. Moisture meters are helpful tools, but they are not diagnostic on their own.
The contractor’s comment that a failed waterproofing membrane would result in a visibly wet floor is not entirely accurate. Many membranes fail in limited areas or develop pinholes, and the leak can track into a wall cavity or down to the slab without the surface ever appearing wet. Likewise, a dry linen cupboard does not rule out early stage waterproofing failure, because the leak path can be very localised. This is why many people rely on a flood test when uncertainty remains: it is one of the few ways to confirm the integrity of the membrane itself. Declining to do a flood test while already onsite does seem unusual, particularly when your concern is specifically about the membrane.
Regrouting alone can improve the appearance and reduce surface water penetration, but grout is not a waterproofing layer. If the underlying membrane is compromised, new grout will not prevent water from entering the tile bed. Regrouting can be a reasonable first step if the grout is visibly failing, but it should not be presented as a guaranteed fix for leaks unless the membrane has been verified as sound.
Given that five different contractors have offered different conclusions without consistent testing, it makes sense that you are unsure. At this point, the most reliable way to get a definitive answer is to engage someone who specialises in leak detection. Ask specifically for a flood test or other membrane integrity assessment. That will give you a clearer picture of whether the issue is superficial, such as failed grout or sealant, or structural, such as membrane failure.
Until you have that information, any recommendation, whether it is regrouting, resealing, or a full shower rebuild, is still partly guesswork. A proper test will give you the confidence to proceed with the right repair rather than relying on assumptions.
Let me know what you think, and if you have further questions, please don't hesitate to ask.
Jacob
