Waterproofing - The Importance of Doing It Right

The Proper Way for installation of waterproofing membrane

Ever wondered why HDB’s waterproofing seems to last for decades, while private home waterproofing can start failing within months? You're not alone. I recently had a case in Tampines that really highlighted this issue.

The Case of the Failing Toilet Waterproofing

Last year, I was called in to redo a toilet where the waterproofing had failed—just six months after a full renovation. The owner had already gone through hacking, re-tiling, and waterproofing, only to face leaks again. I advised him to contact his interior designer (ID) since it was still within the one-year defect liability period.

Unfortunately, the owner had a falling out with the ID and was reluctant to reach out. Still, I encouraged him to send a message—not necessarily to make peace, but to give the ID a chance to rectify the issue. This can help prevent future disputes, especially if back-charging becomes necessary.

Why Are Waterproofing Failures So Common?

As the renovation market gets more competitive, contractors are cutting corners to keep prices low. One area that suffers is waterproofing. And here’s the truth: you can’t shortcut waterproofing. When it fails, the only solution is to hack everything and redo it properly—costly and disruptive.

Many contractors today do waterproofing after plastering and screeding, and often skip the water ponding test—unless you pay extra. Why? It saves them labor and materials. But it’s risky. Here’s why:

Common Mistakes That Lead to Waterproofing Failure

1. Wrong Sequence

   
   

   Waterproofing is often done after plaster and screed to save time, but this results in a 90-degree corner where walls meet floors—a common point of failure.

2. Cracking Cement Layers

   
   

   Plaster and screed cement crack more easily than concrete. Concrete has rebar for reinforcement; cement doesn’t. Once the cement cracks, the waterproofing membrane cracks too.

3. No Protective Screed

   
   

   Tiling directly over the waterproofing membrane leaves it vulnerable. Installing fixtures or accessories can puncture the membrane. A protective screed adds thickness and protection.

The Proper Way to Waterproof (According to BCA Guidelines)

If you're planning a renovation, here’s the step-by-step waterproofing method that actually works:

1. Start After Hacking

   
   

   Patch up wall holes first. Do a 2000mm upturn at the shower area and 300mm for the balance wall. Floor waste pipes should have an upturn of at least 50mm from the finished floor level. Cut all floor pipes to slab level, except the WC pipe.

2. Create Angle Fillets

   
   

   Use cement to form angled fillets at all wall-floor joints. This soft radius helps the waterproofing membrane adhere better and reduces stress points.

3. Apply Waterproofing Membrane

   
   

   Apply two coats. Ensure the first is fully dry before applying the second. Downturn for floor pipes should be at least 50mm. For exposed pipes, upturn at least 50mm above FFL.

4. Conduct a Proper Water Ponding Test

   
   

   Wait until the membrane is fully cured—not just touch-dry—before testing. Many contractors will tell you to test after 4 hours to save a trip, but this risks the integrity of the membrane.

5. Check for Leaks

   
   

   If you're in a flat, you may not be able to check your neighbor’s ceiling. So mark your water level and monitor for drops. Evaporation can happen, but it shouldn’t be significant.

Final Thoughts

Waterproofing isn’t where you want to cut corners. Doing it right adds only 1–2 days to the renovation schedule, but it saves you from costly rework and major inconvenience down the line.

Talk to contractors who specialize in commercial or new build waterproofing—they’re more likely to follow proper procedures. Unfortunately, many residential contractors still opt for the shortcut method, and the results speak for themselves.

So remember: Do it once, do it right. Your future self will thank you.