When adding a footing for a lally column I understand it should be set on level, undisturbed soild ground but should I first put a couple inches of gravel down for drainage. Will water under the existing slab from heavy rains be able to come up through the seam of the new footing? If so, can this be prevented?
Thanks,
Jim

Jim

Since you are adding this footing as a remodel project,

1- make it bigger than necessary, just a little more concrete and with weight on it, the bigger the better. If you can drill holes in the slab and insert some rebar, to tie them together, even better.

2- yes 3-4 inches of 3/4 or larger rock under it is good, don't use small rock or sand.

3-to seal out water get some bituthane, a tar like roofing materials that is just tar in sheet form, and stick it along the sides before you pour. This comes in big expensive rolls, so you may want to just paint it with tar.

Good luck

Roger