Clark, who became Health Minister on October 26, has expressed disappointment that he was told only about the seriousness of one building, the Scott building, not multiple buildings.
The Johnson email contradicts Clark.
But Clark says he has already received an apology from acting board chairman Rabin Rabindran for not mentioning the extent of the problem – which supports Clark's version of what he was and wasn't told on March 13.
Other documents obtained by Stuff includes one written on November 22 for the Ministry of Health which set out the case of $123 million of work needed over multiple buildings at Middlemore hospital.
Clark has criticised former Health Minister Jonathan Coleman for not having been aware of the extent of the problem.
But new National health spokesman Michael Woodhouse said the Johnson emails "indicate that he would have known more than he has admitted to."
"It just beggars belief that he would go to Middlemore Hospital in March to look at a building that has known cladding issues and then not be told about the other issues that they have.
"It seems ironic in the extreme that he would criticise the previous minister for not knowing when he should have and then to claim ignorance of clear advice to at least the ministry about the state of the building stock."
Woodhouse said there needs to be a better understanding of which documents went the minister and when.