Like-for-like sales continued to slow for UK building merchant Travis Perkins in the third quarter as it saw a "very challenging" plumbing and heating market.The company faced some tough comparative figures from the year before, including robust third quarter results, but still grew total sales grew 6.9% and like-for-like sales 5.7%, though this was down from the 10.2% for the first six months of the year.Chief executive John Carter said the results demonstrated "encouraging early progress" in the implementation of management's new strategy."Trading has remained strong for most of our businesses and the group's continued good performance is underpinned by the successful introduction of a number of self-help initiatives," he said."We have outperformed our markets whilst making strategic investments that we are confident will support continued market share gains."However, the plumbing and heating division saw a 5.1% decline in like-for-like sales and 3.2% in total sales.This resulted from the company's branch network reconfiguration, exacerbated by milder weather pushhing the "plumbing and heating season" back, together with lower boiler installations due to a government initiative earlier in the year."It is expected that market conditions will remain challenging for the next six to nine months before the market cycles these temporary effects and strong comparators," the company said.Carter pointed to a better performance from general merchanting with like-for-like sales up 13.3% against 14.6% in the first half of the year, as work to modernise the business progresses.A strengthened management team at Wickes held like-for-likes fairly steady at 6.4%, down from 6.8% in the first half.The contracts business lifted like-for-likes 10.6%, versus 11.1% in the first half as it focused on improving its customer proposition in the face of a slower commercial construction industry.