Supervising Waterproofing: The Hold Points Nobody Should Skip

Waterproofing fails at junctions, penetrations and upstands rather than in the middle of a surface. The supervision sequence that catches it while it is still visible.

Waterproofing is the highest consequence low cost item on most buildings. It is buried within days of installation, its failures appear a season later, and repairing it means removing whatever was built on top. Supervising it properly is a matter of a handful of hold points and a flood test, all of which have to be agreed before the membrane arrives on site.

Before stage one

Before installation begins you need the system approved as a system rather than as a product, the details drawn for every junction, the applicator confirmed as approved by the manufacturer, and the testing regime agreed. Owners who specify a membrane brand and leave the details to the site are specifying a colour, not a system.

• An approved system with the manufacturer specification for substrate, primer, layers and laps.
• Drawn details for upstands, penetrations, drains, movement joints and terminations.
• Confirmation that the applicator is trained or approved by the manufacturer for this system.
• An agreed testing regime, including a flood test where the element allows it.
• A warranty scope understood in advance, including what the manufacturer requires for it to stand.

Stage 1: Inspect and accept the substrate

Check that the surface is sound, clean, at the correct falls, free of standing water and cured as the system requires. Most membrane failures begin here, because a membrane cannot correct a fall that runs the wrong way and will not bond to a contaminated surface.

• Deliverable: A signed substrate acceptance record including falls checked against the drawing.
• Owner: Supervising engineer with the applicator.
• Approval gate: No primer applied before the substrate record is signed.

Stage 2: Confirm falls and drainage before covering anything

Verify falls with a level rather than by eye, and check that outlets sit at the low points. A roof that ponds will eventually find a weakness, and a shower floor that drains towards the door is a defect that will be blamed on the waterproofing.

• Deliverable: A levels record at outlets and high points with the design falls noted.
• Owner: Supervising engineer.
• Approval gate: Any area failing the falls check corrected before waterproofing starts.

Stage 3: Witness the detailing at junctions and penetrations

Inspect every upstand height, pipe penetration, drain connection, corner and termination against the drawn detail. This is where failures concentrate, and it is also the work most likely to be done by whoever is available rather than by the trained applicator.

• Deliverable: A photographic record of every junction and penetration before covering.
• Owner: Supervising engineer, with the manufacturer representative on complex systems.
• Approval gate: Any detail that departs from the drawing rejected rather than accepted verbally.

Stage 4: Check the membrane itself

Verify the number of coats or layers, thickness or overlap, adhesion and continuity. For liquid systems ask how thickness was measured rather than assumed. For sheet systems inspect laps and the treatment of ends and edges.

• Deliverable: A thickness or lap inspection record covering each area installed.
• Owner: Supervising engineer.
• Approval gate: Areas without a thickness or lap record excluded from the valuation.

Stage 5: Flood test and hold it long enough

Where the element can be flooded, fill it and hold the water long enough for a leak to show, with the soffit and adjacent spaces inspected during and after. A brief test proves almost nothing. Record water level, start and finish times and the inspection findings.

• Deliverable: A flood test record with duration, levels and soffit inspection results.
• Owner: Contractor, witnessed by the supervising engineer.
• Approval gate: No protection or screed laid before the test passes.

Stage 6: Protect the membrane immediately

An installed membrane survives days of site traffic, reinforcement being dragged across it and steel props standing on it. Protection is part of the system, not an optional extra, and damage after a successful test is the most common cause of a leak in a correctly installed system.

• Deliverable: Protection layer installed and recorded, with traffic routes controlled.
• Owner: Contractor.
• Approval gate: No follow on trade admitted to the area before protection is in place.

Stage 7: Register the warranty and file the evidence

Collect the material certificates, applicator approval, inspection records, test results and warranty document, then check what the warranty actually requires from you in maintenance. A warranty that depends on annual inspection you never carry out is not protection.

• Deliverable: A waterproofing file including the warranty and its maintenance conditions.
• Owner: Contractor, verified before retention release.
• Approval gate: Retention on the package held until the file is complete.

Handovers between stages

The dangerous handover is from the waterproofing applicator to the next trade, and it usually happens the same afternoon. The membrane is signed off, everyone relaxes, and then screeding, planting, paving or plant installation damages it invisibly. The second is from the contractor to you at handover, when the warranty arrives without the records that make it enforceable.

How you know it is finished

The package is complete when substrate, details, thickness, flood test and protection all have signed records, when the warranty is in your hands with its conditions understood, and when the first rain or the first summer has passed without an issue. Until a season has been through the building, you have documents rather than confirmation.

Domira designs, builds and manages projects across Saudi Arabia for owners who are based abroad: land appraisal, feasibility, design, construction, handover and asset management under one accountable contract. Send us the plot or the brief and Domira will put the numbers in front of you before you commit.