The 15 questions that expose a bad waterproofing contractor before you pay — with what a good answer sounds like, what a bad one sounds like, and a printable checklist.
You cannot inspect a waterproofing job the way you can inspect tiling — the work that matters is hidden inside a slab or under new tiles, and failure shows up months later. So the only quality check available to you happens before the job: the questions you ask at the site visit. Good contractors answer them easily, because the answers describe what they already do. Bad contractors stumble, deflect or get irritated, because the questions expose exactly the corners they plan to cut. Fifteen questions, grouped into five themes, take about twenty minutes to run through — a very good trade against paying RM4,500–RM9,000 (indicative 2026, Klang Valley) for a hacking re-waterproof that fails in a year. This page pairs with our guide on choosing a waterproofing contractor, which covers where to find candidates worth interviewing.
Do three things before anyone arrives. First, document the problem: photos of the stain or drip, when it appears, whether rain or upstairs bathroom use triggers it — this stops a contractor steering the diagnosis toward whatever they prefer to sell. Second, read a benchmark: our waterproofing cost guide gives you the 2026 Klang Valley ranges, so you recognise a fair number when you hear one. Third, decide now that you will not sign anything on the day — the “promotion price if you confirm today” move only works on people who have not decided that in advance. Then invite two or three contractors and ask every one the same fifteen questions.
Q1. How will you find the source of the leak? This matters because the visible stain is often metres from the entry point — water travels along slabs and pipes. A good answer describes a process: moisture meter mapping, checking the floor above, ponding or dye tests if the source is ambiguous. A bad answer points at the stain and says the problem is “there”.
Q2. What else could be causing this, and how will you rule it out? Leaks have lookalikes: condensation on chilled pipes, a failed pipe joint, external wall seepage. A good answer names the alternatives for your situation and how each would be confirmed or eliminated. A bad answer insists there is only one possible cause — conveniently, the one their favourite method fixes.
Q3. Can you show me the evidence before I approve the work? Meter readings, photos from the unit above, test results. A good contractor offers these unprompted, because evidence is how they justify the quote. A bad answer is “trust me, I do this every day” — experience claimed as a substitute for evidence, rather than alongside it.
Q4. Why this method for my problem? PU injection, membranes, torch-on and coatings each fix different failures — see our PU injection guide for when injection is and is not the answer. A good answer connects the diagnosis to the method: this water path, therefore this fix. A bad answer is the same method they quote everyone, whatever the problem.
Q5. What exact system and brand will you use, and how many coats? A good answer names the product line, the primer, the number of coats and the coverage rate — details that can be checked against the manufacturer's datasheet. A bad answer is “good quality German material” with no name, which cannot be verified and usually means whatever was cheapest that week.
Q6. How will you test it before handover? Floors and balconies should get a ponding (flood) test; walls a hose test where practical. A good answer includes the test as standard and invites you to see it. A bad answer is that testing is unnecessary because their work never fails — which is exactly what you would say if you knew it might.
Q7. Is this price flat, or can it grow once work starts? The classic trap is per-point injection pricing where the point count is decided after the pump is running — RM120 a point sounds fine until twenty points appear. A good answer is a flat figure for the defined problem, or a hard written cap. A bad answer is “depends on site condition” with no ceiling. Our waterproofing quotation guide dissects this game with a worked example.
Q8. Exactly what is included — and what is not? Hacking, disposal, new tiles, painting over the stain, scaffolding: the gaps between quotes hide here. A good answer walks you through inclusions and states exclusions in writing. A bad answer keeps the scope vague, which converts later into variation orders you cannot refuse mid-job.
Q9. Can I have that as an itemised written quotation? A good contractor already works this way. A bad one offers a WhatsApp message with a single number — and a single number is not a quotation, it is an opening bid.
Q10. What warranty do you give, in writing, covering what? A good answer states a period, a scope (the treated leak) and a remedy (free re-repair), printed on the quotation. A bad answer is a verbal “don't worry, we cover” — unenforceable the moment they stop answering your calls. Our waterproofing warranty guide explains what these documents should contain.
Q11. What would void the warranty? Honest warranties have stated limits — new renovation works, a different leak source, structural movement. A good answer tells you them upfront. A bad answer is “nothing voids it”, which really means the exclusions will be invented at claim time.
Q12. If it leaks again next month, what exactly happens? A good answer is a process: call, inspection within days, free re-repair if it is the treated fault. A bad answer is vague reassurance — or a fresh charge to come back and look.
Q13. Are you CIDB-registered and SSM-registered, under what name? Registration gives you a legal entity to hold responsible. A good answer is two numbers you can verify. A bad answer is a personal name and a phone number.
Q14. Can I see recent similar jobs or speak to a past customer? A good answer is photos of comparable work — ideally the stages that get covered up — or a referee. A bad answer is stock photos and big claims.
Q15. Who actually does the work — your team or a subcontractor? Subcontracting is not automatically bad, but you need to know who shows up and who carries the warranty. A good answer is direct. A bad answer changes the subject.
| Theme | A good answer sounds like | Walk away if |
|---|---|---|
| Diagnosis | A process: meter, source tracing, tests, evidence | Diagnosis from the stain in five minutes |
| Method | This failure, therefore this method, named system, stated coats | Same method for every problem, unnamed materials |
| Pricing | Flat itemised figure or hard written cap | Per-point count decided after work starts |
| Warranty | Written period, scope and remedy on the quote | Verbal promises or lifetime cover from a new company |
| Credentials | CIDB and SSM numbers, real job photos, named crew | No registration, stock photos, evasive on who works |
Print or screenshot this table and tick answers off during each visit — asking every contractor the same questions is what makes their answers comparable.
| # | Question | You want to hear |
|---|---|---|
| 1 | How will you find the leak source? | A diagnostic process, not a guess |
| 2 | What else could it be? | Alternatives named and ruled out |
| 3 | Can you show evidence first? | Readings, photos, test results |
| 4 | Why this method? | Diagnosis linked to method |
| 5 | What system, brand, coats? | Named, checkable specifics |
| 6 | How will you test it? | Ponding / hose test as standard |
| 7 | Flat price or can it grow? | Flat figure or written cap |
| 8 | What is included / excluded? | Scope stated in writing |
| 9 | Itemised written quote? | Yes, as standard practice |
| 10 | What warranty, in writing? | Period, scope, remedy on the quote |
| 11 | What voids it? | Honest, stated limits |
| 12 | What if it leaks next month? | A concrete free-repair process |
| 13 | CIDB / SSM registered? | Two verifiable numbers |
| 14 | Similar past jobs? | Real photos or a referee |
| 15 | Who does the work? | A straight answer on crew and warranty |
After two or three visits, the decision usually makes itself. Score each contractor loosely across the five themes and weight diagnosis and pricing heaviest — a contractor who diagnoses well and prices flat rarely fails you on the rest. Do not let the lowest number decide: the gap between quotes is usually scope you cannot see, and the cheapest bid most often belongs to the contractor who answered these questions worst. If the leak involves the unit upstairs, settle the who-pays question before committing — our ceiling leak repair guide covers that conversation. And if a contractor was evasive on three or more questions, the answer is no, whatever the price.
We publish this list because we like being interviewed with it. Our answers are on the record: diagnosis before quotation, named systems and stated coats, flat pricing with no per-point counting games — RM650 flat for PU injection of a bathroom ceiling — itemised written quotes, a 6-Month No-Leak Warranty with the remedy stated (free re-injection), CIDB and SSM registration, and our own crews. Ask us all fifteen on WhatsApp before we ever visit — the answers arrive faster than most contractors return a missed call.
Tell us what you need — we reply within the hour.