I'm still very new to all-grain, 7 batches in, so I am still a little shaky with procedure. The other day before my last batch I was re-reading "how to brew and noticed that John Palmer recommends sparging until you have the target amount of liquid in your brew kettle or until you hit a gravity of 1.008-1.012. I don't really understand this. Is this a lower limit? I used 15.4 lbs of grain and at 8.5 gallons it was still 1.051.
First, John's recommendation to stop sparging at 1.008-12 is based on fly sparging. If you batch sparge it doesn't apply to you. The reason he recommends that gravity to stop sparging is that it's an indicator of rising pH, which could pull tannins from the grain. It sounds like maybe you were measuring your wort gravity, rather than the gravity of your last sparge runnings. Is that the case?