Critics ripped Mayor de Blasio Sunday for going along with a $10 million scheme to replace the wood on Coney Island’s iconic Riegelmann Boardwalk with concrete and plastic.

“He’s wrong! This is sabotage!” said Arlene Brenner, a community activist at a Sunday rally on the iconic boardwalk, where others shouted “Vote him out!” and “Leftist liar!”

Even allies blasted the mayor.

“Mayor de Blasio, you’ve got to change the plan,” said Public Advocate Letitia James.

The city has been doing the work in sections since November 2014, replacing portions of wood with recycled plastic slats laid over concrete. The man-made materials are stronger and cheaper to maintain, according to The Parks Department.