Two major reasons for coating concrete are to mitigate corrosion and to stop water contaminants, salts and chemicals getting to the embedded reinforced steel and causing oxidisation, concrete cancer and cracking.
There is a massive range of concrete protection products available that fulfil these objectives to varying degrees, from easy to use acrylic sealers bought in hardware stores to highly sophisticated polyurea coatings which offer a range of benefits to architects and designers.
And now there is one more: Polyurethane Methacrylate.
Polyurethane Methacrylate (PUMA) came about due to some of the limitations of epoxies and urethane systems. Specifically these limitations related to insufficient elastomeric or stretchy properties and their ability to be applied in varying temperature ranges.
PUMA resins can be applied in temperatures as low as -20C and up to 30C making it an innovation applicable to Australia’s climate. The new Royal Adelaide Hospital, incidentally also the third most expensive building in the world, has seen 40,000sqm of PUMA resins applied primarily to waterproof concrete roof decks, court yards, planter boxes and the flagship amphitheatre.
The most important thing, says Sam O’Neill of Poly-Tech Industrial Services Australia, who was contracted to apply the PUMA at the Royal Adelaide Hospital and also works with the whole spectrum of concrete coating products, is that your chosen coating stands up to its environment, has low volatile organic compounds (VOCs), can be installed quickly and has minimal limitations to ambient and concrete temperatures.
“You need to ensure that the coating on the concrete is sufficient for its environment, so if you’re coating a floor with high-foot or forklift traffic you’ll need thicker builds and you might need to make it non-slip if it is to be walked on by the public,” he explains.
“Protecting concrete from cleaning cycles and regimes is also another consideration if you’re in a food processing plant where health and safety of food is an issue because the coating will have to stand up to cleaning chemicals as well as other corrosive factors like blood, fats and oils etc.”
Polyurethane methacrylate systems are applied by hand usually with a primer, membrane, wear layer and top coat.
The major players for protecting concrete and other linings, outside of the basic acrylic sealers, are epoxies, polyurethanes, polyureas and polyurethane methacrylate (PUMA) and companies like Basf, Equus, Sika, Hychem, ERA Polymers, Epirez and Grace Materials can offer versions of most.
“Epoxy is a hard brittle material so offers excellent chemical resistance and where the concrete isn’t going to expand or contract due to temperature variations,” explains O’Neill.
“But where the concrete is subject to temperature variations then you would use a polyurethane based product because it has elastomeric stretchy properties and its physical make up is similar to concrete.”
In a sense, PUMA is a step above epoxies and other polyurethanes, in both its durability—it’s almost bulletproof according to O’Neill—but also in its application timeframes.
It is applied by hand and cures within 30 minutes compared to polyureas which are sprayed on and involve significant piping and masking procedures. When applied properly by an accredited professional, a PUMA resin surfaced area can be returned to service within a few hours meaning no requirements for protection boards and making it appealing for those on tight time-frames.
PUMA resins are also incredibly flexible, around 90 per cent more flexible than epoxies, which make it suitable for areas where natural concrete movement is prevalent—outside for example. They also don’t contain harmful isocyanates like some polyureas and other urethane based products.
A STEP ABOVE POLYUREAS
“We used to use polyureas but we found the way they are dispensed through a spray, and not hand applied, made us constantly weary of overspray because once set it’s very difficult to remove,” says O’Neill.
“You really have to do a major job on mitigating over spray with polyureas.”
Polyureas are hard wearing and extremely robust but they need a lot of masking and overspray protection. They can also be difficult to apply to small crevices and angles and can involve lugging heavy pipes up ladders to different building levels. PUMAs are applied by hand with conventional painters tools.
Because polyureas are based on a thermoset reaction, some linear shrinkage during cure may also occur. If isolated areas are not prepared properly linear shrinkage forces may be strong enough to curl the corners or edges of the applied work and could lead to disbondment from the substrate.
This problem is intensified with polyurea, explains O’neill, because it is applied in a spray process so detailing around drains and corners is trickier and maintaining a consistent depth of cover is challenging compared to the hand applied PUMA systems.
“Polyurea is a robust product, almost bulletproof, but the detailing can be a bit more problematic when you’re spraying into crevices whereas a hand-applied system can be more carefully managed,” says O’Neill.
“When you hear of coatings ‘popping off’ it’s because they haven’t been locked in properly or the substrate was insufficiently prepared.”
But it’s not all positive. Due to the PUMA’s excellent adhesion properties, it means once the coating is down it is incredibly hard to remove and the benefits of its curing speed can also become a detriment if the material sets before application is complete. This can cause bubbles to trap, blisters to form, and lap lines to become visible, ruining an otherwise perfect job.
The system also does not bond well to moist concrete so PUMA resins can only be installed to concrete that has a maximum reading of six per cent or less from a hydrometer.
DON’T GET COMPLACENT
The uniqueness of PUMA technology is not a cause to limit or even eliminate proper, industry accepted surface preparation guidelines—the substrates must be minimum diamond ground, clean, dry and free of contaminants—and this is something O’Neill stressed as incredibly important.
As is the case with most types of concrete coatings O’Neill recommends that architects and designers only use coating professionals with accreditation to use the specified product.
“Make sure you have an approved installer who gets a renewal certificate every 12 months,” he says.
“Just because the installer was approved and accredited five years ago does not mean it remains the case; they might not have those men at the company anymore.”