I have a Morebeer mash kettle and I was suprised by how much space is under the screen. Does all this space affect my calculations for mash thickness? I mean, do I need to add this volume to the mash water to achieve a thin enough mash?
Thanks
I ignore the volume under the false bottom when calculating mash thickness, then just add it to make up for it. For example, if there’s a gallon under the false bottom and you’re mashing 20 lbs of grain at 1.2 qts/lb, that’s 24 qts of water, or 6 gallons, plus 1 gallon from under the false bottom and so I use 7 gallons of water in the mash tun.
Not sure if it’s the right thing to do exactly, but it works for me.
That works for getting your volume out but still dilutes the wort though an additional couple pounds of grain counters that problem.
Yeah, but adding a couple of pounds will thicken your mash. If you’re aiming for a certain thickness then you should ignore the volume under the false bottom IMO. You just end up using less sparge water. Again, I’m not saying it’s right, just the way I do it. 
Oh, I think I figured out what you mean euge. The volume under the false bottom is not the same as the dead space when I drain my keggle, so yeah, accounting for losses to the boil due to dead space in the tun is a different calculation. But for thickness, I subtract out what’s under the false bottom. Hope that makes sense.
Yes it does.
I do the same calculation for water to grist ratio, ignoring the water under the false bottom, but I add that water back into the calculation for the initial strike temperature. You have to account for the entire thermal mass of the water and the tun.
Exactly. Don’t forget this important step. You will be as much as five degrees off with a gallon or so extra water below the false bottom. All that heat gets stirred up into the mash as you mix.