I'm using concrete Sidewalks to raise grade and otherwise resolve issues of waterrunoff and low altitude of construction. The walks are about a meter wide and roughly 4 ". The ground is pretty well packed undisturbed gravelly stuff. So I'm cleaning up, leveling and hand tamping some patches I'm putting into low spots. The thing I'm trying to decide is regarding a number of long rectangular chiseled stone border pieces sunk into the ground approx where I wish to put the outer edge of my forms. imagine something like a stone railroad tie level with the ground. They are nice stones BUT They are Heavy! And they've been there for 40+ years so I don't think they are likely to move much.
One thought is to put my forms right over them, maybe put some mortar mix on them before I pour. My only concern has to do with settling process... I'm not sure how that change in substrate, even if long established may lead to disaster. Also it seems like water might somehow do something bad to it although the stones do supply an extra 6" -ish barrier below surface. The other simple option would be to put the forms just to the inside edge of the stone and thereby not rest any concrete on them and they can stay as sort of footer.. The trick to that is how would I anchor my forms since the stone would prevent driving stakes? I guess this could be done by using a lot of weight... or putting legs on the outside of the forms to bridge the 6" stone bits then drive anchors... Or I have to pull the stones--- yeegads! I'm curious how someone else might solve the issue. Thanks!
If you are going above the stone surface with your concrete, why not use them as the foundation?
They are already firmly settled in place, so they probably won't move.
You will need a bonding agent to get the concrete to adhere to the stones.
Since you are doing 4" of pour, be sure to use a mesh at the mid depth to help hold the concrete together.