What effect did too much water in my mash do???

Well I may have royally screwed up. I looked at the wrong number in Promash and used just over 5 gallons of mash water instead of the 3.5 gallons as I was supposed to for a 10.8# grain bill.

I didn't use as much sparge water as I was supposed to so the final volume balanced out in the end. When I did my efficiency calculations I still got an 80% efficiency in Promash which is the same as my last batch (I've only done 2 all-grains so far). What will this extra mash water do to the flavor of my beer. If it helps I brewed up the Common Room ESB recipe from the database here.

Probably didn't hurt much at all. If you still got 80% efficiency then I'd say you're good. Sometimes if I miss a temp I will add 1 gallon at whatever temp I need to correct things, then subtract it out of the sparge water and call it good. I'm guessing this is one of those mistakes that is not ideal, but in the end really won't matter too much.

yeah, I had a similar problem today. thought i started with 170 dg water, but after I mashed, the temp dropped to 143 dg, I added extra water, still had trouble raising the temp. think my digital thrmometer is acting up. SG came out at 1.039 with an 11 lb grain bill, so i dont think I got a complete conversion.

There is nothing wrong with a thin mash.

I purposely mash thin. Usually in the area of 1.75qt./lb. as opposed to 1.25qt./lb. which seems to be the "norm". I get consistently great results.

You said you adjusted your sparge volume, so you should have no worries.

Thanks for the input everybody. Incase anybody was thinking it, I was not going to throw away the batch. I still pitched the yeast and and will drink the beer. I was just curious if this would have had any effect on the final outcome since I read great comments on this brew.

Thin mashes tend to increase efficiency. It's not unusual for the pros to go 5:1 or even 7:1 (by weight). No impact on flavor that I've ever noticed.