Every month, the CPCA receives hundreds of questions from applicators, specifiers, and curious newcomers to the industry. This month, our technical committee has compiled and answered the ten most frequently asked questions from the past 30 days. Got a question of your own? Submit it here.
Q1: What’s the minimum substrate temperature I can spray polyurea in Canadian winter conditions?
A: The general rule is that substrate temperature must be at least 3°C above the dew point, and typically no lower than +3°C to +5°C for most commercial polyurea systems. That said, the substrate temperature is what matters — not the ambient air temperature. With substrate heating equipment (electric heating blankets, propane heaters, heated enclosures), successful applications at -20°C ambient have been documented. The key is maintaining substrate temperature, monitoring it continuously, and adjusting your application approach accordingly. Our detailed guide on cold weather polyurea application covers this comprehensively.
Q2: How long does polyurea take to cure, and when can I put it back into service?
A: Fast-set polyurea typically reaches tack-free in 2-5 seconds and achieves handling strength in 15-30 minutes. However, full cure — when the coating reaches its design mechanical properties — takes 24-72 hours depending on formulation and temperature. For water-contact applications like cisterns, most manufacturers recommend a 72-hour cure period and sometimes a water flush before returning to potable water service. Always check the product technical data sheet for the specific system you’re using.
Q3: Can polyurea be applied over existing epoxy or cementitious coatings?
A: Yes, but with important caveats. The existing coating must be firmly adhered (pull-off test minimum 1.5 MPa for most systems), clean, dry, and free from contamination. A compatibility test primer may be required. Any areas of delamination, cracking, or disbondment must be removed and the substrate restored before overcoating. Never apply polyurea over a failing or questionable coating — the polyurea’s strength can actually cause the underlying failure to propagate. Our article on Polyurea vs. Epoxy discusses compatibility considerations in more detail.
Q4: What PPE is required when spraying polyurea?
A: At minimum: supplied-air respirator (not just an N95 or half-face cartridge respirator — isocyanates are serious sensitizers), full chemical splash goggles, impermeable gloves (nitrile or neoprene, at least 0.2mm thickness), and chemical-resistant coveralls. In confined spaces, atmospheric monitoring for isocyanate and amine concentrations is required. This isn’t an area to cut corners — isocyanate sensitization is irreversible and can end your career. Provincial OH&S regulations set minimum requirements; the CPCA recommends exceeding these minimums.
Q5: How do I prevent pinholes in my polyurea application on concrete?
A: Pinholes on concrete are almost always caused by outgassing of trapped air or moisture from the substrate during application. Prevention strategies include: test the substrate moisture content (target below 4% by weight), use a penetrating primer or tie-coat to seal surface pores before spraying, apply the first polyurea pass at higher gun pressure to minimize outgassing, and avoid applying in direct sunlight on warm days when the concrete surface temperature may be rising and causing outgassing. On very porous concrete, two primer coats may be needed.
Q6: What’s the difference between aromatic and aliphatic polyurea, and when should I use each?
A: Aromatic polyurea uses MDI-based isocyanates. It’s the workhorse of the industry — cost-effective, strong mechanical properties, and reliable across applications. The limitation is UV stability: aromatic systems will chalk and yellow with prolonged sun exposure. Aliphatic polyurea uses HDI or IPDI isocyanates. It’s significantly more expensive (sometimes 3x the cost) but maintains colour and gloss under UV exposure indefinitely. Use aromatic for anything below grade, enclosed, or where appearance change isn’t a concern. Use aliphatic for exterior decks, roofs, or anywhere long-term colour stability matters. See our overview of polyurea types and applications.
Q7: How do I calculate how much material I need for a project?
A: Start with the theoretical coverage: if your product has a coverage rate of 1.0 L/m² at 1mm DFT and you need 2mm, that’s 2.0 L/m². Then multiply your surface area by that theoretical rate. Finally, add your waste factor: 15-20% for straightforward flat surfaces, up to 30% for complex geometry, windy conditions, or porous substrates. For a detailed breakdown, see our bidding guide: How to Bid Polyurea Projects.
Q8: Is polyurea suitable for potable water contact?
A: Yes — many polyurea formulations are NSF/ANSI Standard 61 certified for potable water contact. This certification must appear on the product’s technical data sheet; do not assume all polyurea systems are potable-water approved. The certification covers both the chemistry and any additives (pigments, fillers) in the formulation. For a detailed discussion, read our cistern lining guide: Sealing Every Drop: Why Polyurea Is the Go-To Liner for Modern Cisterns.
Q9: My equipment is giving me off-ratio mixing. What should I check first?
A: Off-ratio mixing is one of the most common (and serious) equipment issues — it produces a coating that won’t fully cure and has significantly degraded properties. Check in this order: (1) pressure gauges on both sides — are they reading within 10% of each other? (2) Check for any blockage in the filter screens (clean or replace), (3) Check check valve function on both sides — a worn check valve is a very common culprit, (4) Verify material temperatures are within spec, (5) If a proportioner-feed pump is at issue, check displacement seals. Don’t spray until you’ve confirmed ratio is correct — a ratio verification kit (weight test) should be part of every job startup.
Q10: How do I get CPCA certified as an applicator?
A: The Canadian Polyurea Specialist (CPS) certification is available in three levels. CPS Level 1 requires completion of the online fundamentals course plus a practical application assessment at a CPCA-approved facility. Level 2 requires 2,000 documented hours of supervised polyurea application plus passing the Level 2 written and practical exam. Level 3 is our master applicator designation, requiring Level 2 certification, 5,000+ hours of experience, and assessment by a peer committee. Full details are on our Become an Applicator page.
Have a question for next month’s Ask the Expert? Submit your question here. The most valuable questions will be featured in our next edition.
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