How to choose a waterproofing contractor: 8 questions to ask

Most homeowners choose a waterproofing contractor based on price. It's understandable — when you're dealing with a leak, you want a quick, affordable fix. But in waterproofing, the cheapest option is almost always the most expensive one in the long run.

The difference between a contractor who solves the problem and one who creates a cycle of repeated treatments often comes down to their process, not their price. Here are 8 questions that will help you evaluate any waterproofing contractor before you commit.

1. Do you provide a written inspection report?

Good answer: "Yes. We inspect the property before quoting and provide a written report that identifies the source of leaks, the extent of damage, and the recommended treatment."

Bad answer: "We'll take a look and give you a quote."

Why it matters: A contractor who inspects before quoting is trying to understand the problem. A contractor who quotes without inspecting is guessing — and you'll pay for that guess when the treatment doesn't work.

2. What materials will you use?

Good answer: Specific brand names, product types, and why those products are appropriate for your specific situation.

Bad answer: "We use the best materials" or "imported chemicals" without naming specific products.

Why it matters: Vague answers about materials usually mean the contractor will use whatever is cheapest or most readily available. Specific answers show they've thought about what your situation actually requires.

3. How many layers, and what is the curing time?

Good answer: A clear breakdown — primer, base coat, reinforcement (if applicable), top coat — with specific curing times between each layer.

Bad answer: "We'll do two-three coats" with no detail about curing or reinforcement.

Why it matters: Proper waterproofing requires multiple layers with adequate curing between each. If a contractor can't explain their layering system, they probably don't follow a structured process.

4. Do you provide a written warranty?

Good answer: "Yes. Our warranty is written, specifies the coverage period, what's included, and what's excluded."

Bad answer: "We guarantee our work" (verbally, with no documentation).

Why it matters: Verbal warranties are worthless when leaks return 18 months later and the contractor doesn't answer the phone. A written warranty with clear terms shows accountability.

5. Will you do surface preparation and slope correction?

Good answer: "Yes. We prepare the surface by removing old coatings, repairing cracks, and correcting slope where needed before applying the membrane."

Bad answer: "We'll coat over what's there."

Why it matters: Surface prep and slope correction are the most important (and most skipped) steps in terrace waterproofing. Without them, even premium membranes will fail. A contractor who skips preparation is saving time at the cost of your treatment's longevity.

6. How do you verify the work?

Good answer: "We flood-test the treated area for 24-48 hours after the membrane has cured. For walls, we may use thermal imaging to verify moisture levels."

Bad answer: "You'll see — it won't leak."

Why it matters: Verification testing is the quality check that confirms the treatment works. Without it, you're trusting that everything was done correctly — and you won't know otherwise until the next rain.

7. Are your teams in-house or sub-contracted?

Good answer: "We use our own trained teams. They work under our supervision and follow our process standards."

Bad answer: "We have different teams depending on availability."

Why it matters: Sub-contracted labour introduces inconsistency. Different teams may follow different processes, use materials differently, or skip steps. In-house teams are trained on the same process and held to the same standards.

8. What is the timeline and payment structure?

Good answer: A clear timeline with milestones, and payments tied to completion of each stage — not demanded upfront.

Bad answer: "We'll start when you pay" with 100% advance payment required.

Why it matters: Milestone-based payments align the contractor's incentive with your interest — they get paid as they deliver results. Full advance payment removes their incentive to finish on time or address issues.

Red Flags

Beyond the 8 questions, watch for these warning signs:

• 100% advance payment: Any contractor requiring full payment before starting work is a risk. A reasonable advance (20-30%) is normal, but the majority should be tied to milestones or completion.
• No written quote: If the quote is verbal or vague ("approximately this much"), you have no basis for comparison and no record of what was agreed. Insist on a written, itemised quote.
• Pressure tactics: "This price is only valid today" or "we're fully booked, you need to decide now." Good contractors don't need to pressure you. If they're applying urgency, it's usually to prevent you from getting a second opinion.
• Suspiciously low price: If one quote is significantly lower than others, ask why. They may be using cheaper materials, skipping surface prep, or planning fewer layers. The low price often reflects shortcuts that will cost more later.

The Bottom Line

Choosing a waterproofing contractor is really about choosing a process. The right process — proper inspection, accurate diagnosis, quality materials, skilled application, and verification testing — produces results that last. The wrong process produces results that look fine for a few months and fail when they're tested.

These 8 questions won't guarantee a perfect outcome, but they'll help you distinguish between contractors who follow a disciplined process and those who don't. Transparency and documentation are non-negotiable. If a contractor can't clearly explain what they'll do, how they'll do it, and how they'll prove it works — keep looking.