Most civic engineers feel the extra investment of Rs 25 crore that mayor Subrata Mukherjee has decided to make to cover with mastic asphalt more than two dozen city thoroughfares will be counter-productive as the coat may not be long-lasting.

?Instead of road repair, the civic road department is carrying out what can be dubbed resurfacing roads. Neither will it last, nor improve road conditions,? they stress.

Since the top coat of existing bituminous roads is not being dug up before applying mastic asphalt, the top layer of mastic will lack adequate grip.

Moreover, as potholes are not being filled up first before applying mastic asphalt, the road surface will be wavy at places, particularly at bus stops, where buses apply brakes frequently.

With the extra funds allotted by the mayor, the civic engineering department has started converting important city thoroughfares from bituminous to mastic asphalt-coated roads.

Director-general (civil) Uday Shankar Sengupta denied the charge, saying adequate care has been taken to maintain the alignment and camber of the roads.

He said mastic asphalt, though costlier, lasts much longer than bituminous roads.

Besides, he stressed, whereas bituminous roads are not resistant to water, a mastic asphalt-coated road does not develop potholes after waterlogging.

Admitting that in some parts of the city, particularly in some narrow roads in central and north Calcutta, the surface of the roads is higher than the entrance of the buildings abutting them, he said it will take time to correct the alignments manually.

The roads to be made over with mastic asphalt include Bidhan Sarani, MG Road, Rabindra Sarani, CIT Road, Shakespeare Sarani, APC Road, Raja Rammohun Roy Road (Amherst Street), BB Ganguly Street, Palm Avenue, Rafi Ahmed Kidwai Road, Hazra Road, Circular Garden Reach Road, Deshapran Sashmal Road, Rashbehari Avenue, Rifle Range Road, Biren Roy Road, Chetla Road, Raja Subodh Mullick Road, Ganesh Chandra Avenue, KK Tagore Street, Ahiritola Street and Bagbazar Street.