A warning to the government several years ago over the risk of concreting jobs being done badly due to a lack of regulation is now being downplayed.

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The National Party is accusing the Minister for Building and Construction of doing nothing about the risk.

Documents show that industry lobby group Concrete New Zealand asked two years ago for more training and regulation.

"Many issues with the durability of concrete can be directly related to the proficiency of the concrete placer," it stated, in a briefing to Minister for Building and Construction Jenny Salesa.

It was an unregulated area, with no barriers to entry for concrete workers, made worse by the sector's skills shortage.

"A potential consequence of this lack of hands-on expertise ... is that the competency of concrete placers may be poor, which in turn could lead to poor concrete performance," the document stated.

Salesa told Parliament late last year, in answer to questions from National, that she did not seek more advice about this or discuss concrete worker training with the Minister of Education.

She did not respond to an RNZ request for comment.

Late last year, Salesa was confronted by a Wellington scanning company's findings, that many major buildings had flawed concrete in them, including some with multiple serious voids, or hidden gaps, that reduced the strength of floors and walls.

She ordered the Ministry of Business, Innovation and Employment to look into the findings, but it had not verified them or otherwise.

"MBIE has and continues to engage with Engineering New Zealand and councils, but without being able to identify specific buildings, verification is limited," it said.

Concrete New Zealand is now downplaying the concerns it raised in the December 2017 briefing.

It "occasionally fields calls in which the quality of the concrete 'finish' is questioned", its chief executive Rob Gaimster told RNZ in a statement, having declined an interview.

"These instances relate to aesthetics and are generally confined to a residential setting involving driveways, paths and patios."

When RNZ questioned why it would raise such a seemingly trivial matter about how driveways look, in its first briefing to the incoming minister, when the construction sector was grappling with so many major problems, the group said "this was one of a number of topics" raised.

Also, the concern raised originally was about concrete placers, not concrete finishers.

Gaimster pushed back over the competency warning his group had issued, saying the "vast majority" of workers were competent, training was being promoted and guidance reviewed.

"The feasibility of introducing an industry-managed, audited concrete contractors' scheme, which would cover placing and finishing, is currently being assessed."

However, in its briefing to Salesa, the group had said the government should help to produce training programmes modelled on those overseas, and include a concrete worker category in the Licensed Building Practitioner scheme run by the Ministry of Business, Innovation and Employment.

Asked about this, the ministry told RNZ that quality controls on concrete were adequate.

"Current construction monitoring and quality control processes, in conjunction with BCAs [councils], is the appropriate place to manage the potential risk," it said.

As for training, Concrete New Zealand could help set this up under the Construction Sector Accord, it said.

The National Party's construction spokesperson, Andrew Bayly, said the minister's inaction was unacceptable given the importance of concrete in construction.

"She's confirmed that she hasn't actually done anything about it," Bayly said.

"There are concerns that we don't have people being trained adequately to make sure the concrete is vibrated and put in place properly to meet all the concrete requirements and the industry has highlighted the issue to the minister."

She could at least have raised the matter of training courses for concrete workers with the Minister of Education, Bayly said.