Two classrooms were shut last week at Groeslon primary school, Caernarfon, after the faults were found.
Portable buildings are being installed after independent structural engineers recommended that the school’s 1960s-built classrooms be closed on safety grounds.
Pupils are due to be taught in the school hall until the temporary buildings are ready.
But parents are not happy about letting their children enter the building.
Parent Richard Birch told the BBC: “The plan is that we are going to take the children to the school in uniform but not let them go in [on Tuesday].
“Obviously on Wednesday they will have to go to school.
“The classrooms were condemned last week.
“In the middle are the halls and toilets but whenever it rains there are buckets in the hall to catch the rain water. How can you condemn the two ends but not the middle?”
Gwynedd council said Welsh government funding for a new school was in place, but would be released only once the council demonstrated how it intended to reorganise education.