A section of the new road surface had failed to meet the required quality standards, meaning it needs to be resurfaced during the construction season starting in spring.
Since the failed assessment, the agency has been ferreting out "the right solution".
Stephen Collett, regional manager Tāmaki Makaurau me Te Tai Tokerau at Waka Kotahi, said they worked closely with their contractor to agree on a remedial plan now in place for the critical part of Northland's transport network.
But they arrived at the solution at the same time as the rain, ruling out the possibility of resurfacing because water can compromise the integrity of the road structure's base layers.
"The remedial works required are very weather dependent – with warm, dry conditions imperative when laying a permanent road seal," Collett said.
"Waka Kotahi would like to apologise for the inconvenience this issue has caused. We understand people are keen to see this work completed as soon as possible," he said.
To keep the road usable during winter, Waka Kotahi had laid a temporary seal that will receive road markings once drier weather sets in.
"We understand locals and those who travel through the area will be frustrated to hear the repairs can't take place until spring.
"However, we want to reassure people travelling through the area that we remain 100 per cent committed to ensuring the final product is a safe, fit-for-purpose road."
Waka Kotahi confirmed the spring remedial works would complete stage one of the Loop Rd safety improvement project, which holds the title of Whangārei's largest road construction project.
The Advocate has approached Waka Kotahi to find out whether the delay will push the completion of stage two past its 2022 deadline.
Construction at the highly congested intersection has already dragged out, with Covid-19 the culprit for previous delays.
Waka Kotahi previously told the Advocate that supply issues due to lengthy lockdowns in Auckland had caused setbacks.
