Cr Kathy Dennison raised the issue after getting ''numerous complaints'' the metal was shredding tyres.
The council moved quickly to resolve the problem, putting smaller-sized metal down, then grading and rolling the roads.
Chief executive Michael Ross said the council was using a new source of metal because it lasted longer and was about 20% cheaper.
''It is a matter of trying to do more with less, but some times there are consequences and we have to learn from our mistakes,'' he said.
The unsealed roads affected were Taieri Peak and McLew Rds, which are expected to come under increasing pressure from logging trucks.
Roading manager Michael Voss said the council worked with contractor SouthRoads to source local metal supplies and keep costs down, enabling any savings to be reinvested in roads and maintenance. The aim was to do more with the same amount of money and provide road maintenance at the best possible cost to ratepayers.
The recent use of metal from Palmerston gave the ability to increase work by 20%, compared with an alternative product sourced elsewhere.
''Unfortunately, we experienced some problems when some of the rock fractured the wrong way and left some sharper than usual stone.
''We have now addressed this by improving both the materials selection and the application methods,'' he said.
This metal was also chosen as it provided extra strength to the road foundation, needed because of more intensified logging operations planned in the area. The material was used by other roading contractors and the problem was unexpected.
''We will continue to monitor the situation as we attempt to find roading solutions that are acceptable to road users without being too high a burden on ratepayers,'' Mr Voss said.
Anyone with issues should contact the council.
