Mud Sill TIP for Humpy Foundations
Use thick mudsills to span uneven expanses of an old foundation. Fill in with mortar after the sills are flat.
When an old house comes down to the foundation, you have a clean slate for plumb, level, and square.
Humpy old foundations can be a bad starting point. To make sure the floor framing is level, begin by shimming the mudsills using a transit or laser.
To reduce the effects of out of level corners and big humpy bumps, use thick mudsills that can be half-lapped at the corners. Screw the corners together to create a stable structure less prone to variations in the foundation.
You can staple the sill seal to the bottom of the mudsill before laying it down, and the masons can fill the gaps under the mudsill with mortar.
Now you’ve got a solid flat substrate to frame a floor on that will be level and flat.
—ProTradeCraft is covering the 2017 Model Remodel project in 'real time,' and this is one nugget of info gleaned from its circumstances.