DIY firm Grafton Group said it remained positive despite modest margins in a competitive market.In a trading update on Thursday, the company said revenue for the six months to June 30 increased by 6.6% from to £1.015bn to £1.08 bn, despite weaker pricing in the UK plumbing and heating market and a competitive market.Grafton said overall group operating margins were expected to be modestly ahead of the first half of 2014 before property profits."The anticipated momentum in growth in the UK has not yet gained the consistent traction expected although the overall trajectory remains favourable," the company said in the update.In its merchanting division, which accounts for 91% of group revenue, the company reported growth in average daily like for like revenue.However, Grafton noted this was partially offset by a lower gross market due to competition and mix changes.Grafton chief executive Gavin Slark said despite current challenges, it would deliver the group's medium term targets. At 0806 BST, Grafton shares were down 0.91% to 760p.