Perform the Flood Test
The flood test is your last chance to verify waterproofing before tile installation. A simple 24-hour test can save you from costly water damage repairs down the road.
Quick Summary
Why Flood Testing Matters
Once tile is installed over your waterproof membrane, finding and fixing a leak becomes extremely expensive—often requiring complete demolition of the new tile work. The flood test is a simple, low-cost verification that your waterproofing is working correctly. It's often required by building codes and is always recommended best practice.
What You'll Need
- •Drain plug or test ball - Inflatable or mechanical plug that seals the drain
- •Water source - Garden hose or bucket
- •Marker or tape - To mark water level
- •Access to area below - To check for leaks (crawlspace, basement, or lower floor)
How to Perform the Flood Test
Wait for Full Cure
Before flood testing, ensure waterproofing is fully cured:
- Liquid membranes: Usually 24-72 hours (check product label)
- Sheet membranes: Usually 24 hours after installation
- Hot-mop: Usually 24 hours after installation
- Mortar bed with liner: After mortar has cured (24-48 hours)
Plug the Drain
Choose an appropriate plug for your drain:
- Inflatable test ball: Insert into drain pipe and inflate
- Mechanical test plug: Expands with a wingnut
- Expandable rubber stopper: Budget option
Important: Don't use rags or plastic bags to plug the drain—they can slip and cause flooding. Use a proper test plug.
Fill with Water
- Fill shower pan with 2-3 inches of water
- Water should cover the entire floor area to the curb
- Fill to just below the curb top (leave 1/2" margin)
- Be careful not to overflow onto unprotected areas
Mark the Water Level
- Use painter's tape or marker on the wall to mark exact water level
- Mark in multiple spots for accuracy
- Note the time you started the test
- Take a photo for documentation
Wait 24 Hours
- Leave water undisturbed for 24 hours minimum
- Some codes require 48 hours—check local requirements
- Check periodically for obvious leaks below
- Don't add or remove water during the test
Pro tip: If you have access to the area below, tape a piece of cardboard or paper towel to the ceiling. Any drips will be immediately visible.
Check Results
Test passes if:
- Water level has not dropped at all
- No moisture visible below the shower
- No damp spots on surrounding walls
Test fails if:
- Any drop in water level (even 1/8")
- Any moisture or drips below
- Wet spots on walls or subfloor
If the Test Fails
Do NOT proceed with tiling. Find and fix the leak first.
Common leak locations to check:
- 1.Drain connection: Most common failure point. Check seal between drain and membrane.
- 2.Curb corners: Check where curb meets walls and floor.
- 3.Wall-to-floor transition: Especially at corners.
- 4.Membrane seams: Any overlap or joint in the membrane.
- 5.Pinholes: Small holes in liquid membrane from improper application.
After repairs, wait for full cure and retest. Repeat until the test passes.
Documentation
Document your flood test for warranty and permit purposes:
- □Photo of filled shower with water level mark visible
- □Photo of area below shower at start of test
- □Photo after 24 hours showing water level unchanged
- □Photo of dry area below after 24 hours
- □Note date, duration, and results of test