How do I fix this incorrectly waterproofed linear drain?

diydunce

I just bought a house and we've found water. I've traced the leak to the shower drain.

The shower drain is a linear trench drain, an older design where the grate & tray have minimal overlap and meet in the middle of the depth of the trench (the modern ones are different and appear to have the tray extend the full depth of the trench, near flush with the tiles). There appears to be missing waterproofing around the end of the trench. The area hasn't been kept clean, the drain has been slow draining and filling the trench with water and running off into the gap I've found.

Picture of side of drain:
- top layer tile

- mid layer blue waterproofing?

- bottom layer, spongey damp and totally falling apart brown something (wood?) where water has been running off when someone showers

Picture of side of tray that fits on inside of the the steel trench, note there's not much overlap on the steel & gaps on the side:

I've used a dehumidifier for a couple of weeks to get as much water out as possible of that gap, unclogged the drain and will be vigilant about keeping it clear draining to reduce the risk of water draining off into this space in the future, but I'm not sure how to best fill the gap & waterproof this? It needs to withstand the constant pulling up of the grate to clean the tray, so imagine it'll get rubbed a bit. The drain doesn't appear to be a standard size (866x95mm), otherwise I would also look to replace this with the more modern styles of these trench drains with a deeper tray and shallower grate.

I appreciate any fix will be temporary until I can find funds for a bathroom renovation. Thanks for your help in advance!

MitchellMc

Welcome to the Bunnings Workshop community @diydunce. It's terrific to have you join us, and many thanks for your question about repairing waterproofing.

It sounds like you've done a great job identifying the source of the problem and doing what you can in the short term to manage the issue, especially by clearing the drain and using a dehumidifier. Unfortunately, though, when it comes to a failed or incorrectly installed waterproofing system, particularly in wet areas like a shower, it really needs to be addressed by a qualified waterproofer. In many areas, waterproofing must be carried out by a licensed professional to comply with building regulations. If you were to attempt a DIY fix and further water damage occurred later, you could run into trouble with your home insurer if they ask for evidence that the issue was corrected by a qualified tradesperson.

That said, a waterproofer might use a product like Sikaflex 11FC or a similar polyurethane sealant to seal the visible gap. It's flexible, durable, and waterproof, which makes it suitable for areas that experience movement or wear, such as a drain cover that's regularly lifted. However, this would just be one part of the job. The professional might need to remove sections of the existing shower base to properly apply or repair the membrane and bring the whole assembly back up to standard.

To resolve it properly and protect your home long term, I’d recommend getting a quote from a licensed waterproofer for repair options. They’ll also be able to confirm whether any building code violations exist and what’s involved in a compliant fix.

Please let me know if you have any questions.

Mitchell