How to test whether waterproofing has failed?

LorenClayton

Hello

This has been an ongoing saga for the past year since I bought this house. At that time, building inspector had said shower had a slight leak to the wall & recommended plumber's investigation. Just had a contractor come out recently for a free shower leak test, which he didn't do as he said there was no need. His moisture meter had 99% on the bathroom floor, however he said if the waterproofing had failed then the floor would be noticeably wet, which it isn't and never is. The linen closet on the other side of the shower is also completely dry. His view was that there is leakage, but that it is all going through the grout in the shower pan & wall tiles as he can see that the grouting has failed. He said that the shower just needs removal and re-grouting ($1,600). 

Their company's online profile alludes to their staff's carpentry experience, but no waterproofing or tiling experience, so that threw me a bit. I'm also surprised that seeing as he was there anyway, it wouldn't have hurt to do the flood test, for piece of mind if nothing else, but he was adamant this wasn't needed.

Over the last year I've had about 5 quotes, all saying something different. Two recommended a shower seal to replace the "broken waterproofing" even though this wasn't tested, One said his moisture meter indicated waterproofing failure, but didn't specify why he was so sure it was the waterproofing and not the grout. Others also suggested just resealing the grout.

So there's no definitive test to prove once and for all whether or not the waterproofing is OK? I hope someone there can help and thank you, guys.

JacobZ

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