"People at that site had all their workers in masks and implemented sign-in procedures within 30 minutes of not getting the product delivery. You can't do much without concrete," he said.
Lack of mandatory face-mask rules has sparked alarm in the sector which wants an authority to make them compulsory on building sites at alert level 3, Leys said.
Construction Health & Safety NZ says face masks are not compulsory under level 3, Leys said.
But Delta changed the risk, "so we are calling on CHASNZ and the Construction Sector Accord to urgently update the protocols to include the mandatory wearing of masks", Leys said.
"Most construction or building sites and manufacturing plants and warehouses are not yet back at 100 per cent of their workforce because of 2m social distancing rules. We are probably talking about hundreds of workers not wearing masks on sites," he said.
A Herald inquiry to CHASNZ resulted in being told: "It's confusing. You're not the first to ask. The Ministry of Health doesn't say yes or no about face masks on construction sites but it talks about the risks of not wearing one and refers people to the Unite Against Covid website which says people in offices or factories don't have to but people in public-facing roles do."
Master Builders says face coverings continue to be mandatory in all in-door venues and all public-facing staff must wear them.
Leys said he had spoken to a Ministry of Business, Innovation and Employment official about the situation. He wants the Government to make face masks on building sites compulsory even under alert level 3.
Most big building firms had on their own accord introduced face mask-wearing under alert level 3, Leys said, because they knew Delta was so much more contagious.
"Construction sites are by their very nature some of the most dangerous workplaces in New Zealand requiring extra vigilance and health and safety measures to protect workers such as hi-viz clothing, gloves, safety glasses, hardhats," he said.
Ironically, masks sometimes caused health and safety risks, especially when people were using nail guns and other dangerous equipment. Fogged goggles were not an option, he acknowledged.
"Similarly, crane drivers operating and moving massive pieces of equipment do so from the confines of a cab, metres above the ground and so need a non-interrupted line of sight. Crane drivers are supplied masks but during operation in the cab don't necessarily have to wear them because of the distance from other workers and the danger of their work," Leys said.
But changing the type of mask and glasses worn so that fogging did not occur was one solution, he said.
"These are all incremental changes which will be made along the way by the building and construction sector but fundamentally mask wearing should be a mandatory requirement to prevent the spread of Delta," he said.
Peter Reidy, Fletcher Construction chief executive, said earlier this week that face masks would be worn on that company's Auckland sites.
Fletcher had safety protocols under alert level 3: additional physical distancing, mask-wearing, separating entry and exit points on site and hygiene and tracking and tracing measures, he said this week.
Sean Sweeney, City Rail Link chief executive, also cited masks in that workforce's return to work yesterday.
Strict health and safety protocols are in place on CRL sites, he said, including physical distancing, health monitoring, enhanced cleaning, segregation between different work crews and wearing personal protective equipment including masks.
