I also try to make sure that I have two people working on the wall repair and, while they are, I completely ignore everything else until it's done. Doing it this way, I have never had to buy more than one of the wall repair compounds like I've read that some other people have. Oh, and as long as they are at least 14, they can work on it.

Personally, I actually keep my peeps working the the floor repair stuff too, even though I know it won't dry up like the wall repair compound. Mainly because I just like to see it get done though. I'm one of those people that don't like to leave a task in the middle and I guess that carries over into my games too, lol!