Actually, he'll probably work better than some others as he won't take so much time off. However, he'll do the work a lot slower than the others.

How experienced are they? Untrained, trainee, adept? Do they have building checked in their details? To start a new builder off can take several attempts before they learn enough to become trainees. It is usually best to start training them by setting them to fix a hut or repair the loveshack. That's because they don't have to travel far so you can keep an eye on them and drag them back to work if they fail. Once they become a trainee you can put them to work on another task and can usually leave them to get on with it, although most will wander off from time to time for a crafty swim in the pond or whatever.