TPI Composites has reported its financial results for the third quarter ended September 30, 2018. Net sales for the quarter increased by $1.5 million or 0.6% to $255.0 million compared to $253.5 million in the same period in 2017. Total billings decreased by $15.7 million or 6.1% to $240.7 million for the three months ended September 30, 2018 compared to $256.4 million in the same period in 2017.
Net sales of wind blades were $234.9 million for the quarter as compared to $238.1 million in the same period in 2017. The decrease was primarily driven by a 19.1% decrease in the number of wind blades produced during the three months ended September 30, 2018 compared to the same period in 2017, primarily as a result of the increase in lines in transition, the lost volume from two contracts that expired at the end of 2017, a delayed customer startup and by foreign currency fluctuations.
Total cost of goods sold for the quarter was $238.0 million and included $19.0 million related to startup costs in their new plants in Turkey, Mexico and Iowa, the startup costs related to a new customer in Taicang, China and transition costs of $2.4 million related to the six lines in transition during the quarter. This compares to total cost of goods sold of $223.2 million for the same period in 2017, which included $12.4 million related to startup costs in our new plants in Turkey and Mexico and the startup of a new wind blade models for certain customers in Turkey and Dafeng, China.
General and administrative expenses for the three months ended September 30, 2018 totalled $9.8 million, up from $9.3 million for the same period in 2017. Net income for the quarter was $9.5 million as compared to $21.7 million in the same period in 2017. The decrease was primarily due to the reasons set forth above. EBITDA for the quarter decreased to $7.4 million, compared to $26.8 million during the same period in 2017. EBITDA margin decreased to 2.9% compared to 10.6% in the same period in 2017. Adjusted EBITDA for the quarter decreased to $17.6 million compared to $27.9 million during the same period in 2017. Adjusted EBITDA margin decreased to 6.9% compared to 11.0% during the same period in 2017.
During the third quarter, the company expanded an existing multiyear supply agreement with Vestas for two manufacturing lines in their new manufacturing hub in Matamoros, Mexico; they expanded a supply agreement with GE in Mexico with GE agreeing to add two more production lines, transition three of the existing lines and extend the contract by two years; and finally, GE agreed to transition to a larger blade model in our Iowa plant in early 2019.