A Building Surveyor who specializes in acting as 'Expert Witness' will provide you with an expert and independent opinion on the quality of work and the materials used. Importantly, this Expert Witness report will be accepted as highly reliable and independent evidence in court should you need to take it this far. Its highly likely, however, that your builder will recognise the strength of your experts role and opinion, making him far more inclined to put things right. He knows he's up against a highly knowledgeable professional who's independent evidence will be relied upon in court, should this be needed! The problem with getting the opinion of another builder, rather than an Expert Witness, is that the builders report will never be viewed as independent. The Expert Witness report, however, is legally defined as independent.
I've used Expert Witness Building Surveyors in the past. They've been worth their weight in gold. Look to pay approximately £60- £80 per hour. For this, they will come and inspect the work and materials, provide a report containing a detailed breakdown of defects, then stipulate what needs doing to remedy the problems. Should you wish, they can even arrange for the remedial work to be carried out by their own recommended contractors. For something as straightforward as you describe, the surveyor would probably need less than an hour to deal with it (they're very quick). Its definately worth the money as without this Expert Witness report one can spend weeks or even months chasing up builders and getting nowhere.
Should you decide to go down this route, remember to look for a Chartered Building Surveyor who has undergone training as Expert Witness. They often advertise this particular aspect of their work. You'll find them online, in Yellow Pages or by contacting RICS (Royal Institute of Chartered Surveyors) who should be able to give you info on suitable members working in your locality.
Good luck.
