Foundations of concrete are indestructible.
At necessary points, remove a few stones or bricks, as the case may be, inserting short pieces of heavy timber to wedge or jack up the building. Carefully raise the building, by this means, until it stands free of all foundations. Remove all the old stone or brick foundation to be replaced, and set in place the forms for the concrete.
Small buildings can usually be raised high enough to allow working room, whereby the form may be filled right up to the top with concrete. The mixture should be a wet one. (Proportions, 1: 2: 4.)
Where buildings are too cumbersome to be raised by “jacking,” to a sufficient height to give head-room, it will be found necessary to make the foundations 3 inches wider than the sill. Carry the forms to the desired height and utilize this extra 3 inches of width for placing the concrete in the forms. The top board of the forms may also be left off until you are ready to place the last of the concrete. In this case the last batch of the concrete should be very wet. Tamp the concrete until it comes up flush with the bottom of the sill, to the entire width of the wall.
Be sure to leave a space in the concrete wall, under and on the sides of the underpinning support, so that the building may later be lowered back onto the new foundation and the timber removed. This opening must be slightly larger than the underpinning support. After the building has been lowered fill these openings with concrete. Lower the building after the foundation has been in two weeks.