Trade walkthroughs
How to inspect waterproofing
Waterproofing only fails at the places it isn't continuous: a lap that didn't bond, a penetration sealed with caulk instead of a boot, a termination that stops short of the finished grade. All of it gets covered — by backfill, by a topping slab, by insulation and cladding — so the inspection has to happen while the membrane is still exposed and the details can still be corrected.
For the superintendent or envelope QC lead verifying below-grade and horizontal waterproofing against the details before it's protected and covered.
Step by step
Confirm the substrate is ready to receive membrane
Check that the concrete or masonry is cured, clean, dry, and profiled per the manufacturer's requirement, with no laitance, form oil, honeycomb, or standing water. Tie holes, cracks, and rough spots have to be patched and cants formed before any primer or membrane goes down.
Verify the right system and primer for the condition
Confirm the membrane type — sheet, fluid-applied, hot or cold — matches the submittal for that substrate and exposure, and that the primer is the specified product applied at the right rate. A fluid-applied membrane at the wrong wet mil thickness is the defect you can't see once it skins over.
Check laps, bond, and continuity across the field
Walk the field for lap width, full adhesion with no fishmouths or wrinkles, and consistent thickness. On sheet systems probe the seams; on fluid-applied confirm wet or dry mil readings were taken at the required frequency. The field is only as good as its weakest lap.
Inspect penetrations, corners, and transitions
Every pipe, sleeve, tie-back, and change of plane gets reinforced with detail strips, target patches, or preformed corners before the field membrane, not caulked afterward. Inside and outside corners and cove transitions are where hydrostatic pressure finds the weak point.
Verify terminations and tie-ins
Confirm the membrane terminates into a reglet, termination bar, or the specified detail, and that it laps correctly with adjacent waterproofing — the footing, the slab, the wall membrane above. A termination that dies into open air or reverses its lap is a leak path by design.
Confirm drainage, protection board, and flood testing
Verify drainage composite, protection board, and any drainage mat are installed before backfill, and where a horizontal deck or plaza is waterproofed, confirm the flood test is run and held for the specified duration and passes. Water finds the holiday the flood test is there to reveal.
Document each area before it's covered
Photograph the completed membrane, the reinforced details, and any flood test against the checklist before protection board, backfill, or topping hides it, and log any holiday, thin spot, or bad termination as a nonconformance to close before cover.
What gets missed
- Applying membrane over a green, dirty, or damp substrate that never lets it bond.
- Caulking a penetration instead of reinforcing it with a boot, detail strip, or target patch.
- Skipping wet-mil checks on fluid-applied membrane, so a thin coat looks finished and fails.
- Backfilling or placing topping before the flood test and detail photos are done.
- Terminations that stop short of finished grade or reverse their lap against the adjacent membrane.
Questions people ask
- What's the difference between waterproofing and dampproofing?
- Dampproofing resists moisture vapor and incidental water; waterproofing resists hydrostatic pressure — standing water pushing against the assembly. They're different products and different details, so confirm which one the spec actually calls for before you inspect against it.
- Why flood test a horizontal membrane?
- Because a pinhole or unbonded lap won't show under a light rain but will leak under standing water. The flood test loads the membrane the way service will, holds it, and proves the details before a topping slab or planting covers them for good.
Terms worth knowing
Checklists that make this a one-tap job
Free, field-ready checklists, each with the photo every item needs before it can be submitted.
Related guides
- How to inspect the building envelopeInspect the envelope as a system — air barrier, water-resistive barrier, flashing, transitions, and sealants — with the continuity and mock-up that make it perform.
- How to inspect sealants and caulkingInspect sealants and caulking the way a joint fails — substrate and prep, backer rod and joint dimension, tooling, adhesion, and the right sealant for each substrate.
- How to inspect a roofWalk a roof the way it goes together — deck, dry-in, flashing, penetrations, edge metal — and catch the leaks at the details before they're covered.
Reading the steps is one thing. Proving you walked them is the job.
RTI holds the submit button until every mandatory item is answered and the photos are attached, then chains the record so it can be proven untouched later.