On Jan 5, 2:54*pm, "JEEPR" wrote:
I have an 11 inch diameter hole, for an old fire place chimney stack in the
basement foundation. The foundation is cinder block. I have currently sealed
off the hole from the outside of the basement with a overlapping sheet of
1/4 inch plywood.
What is the best way to seal or plug this large hole? Also is any
reinforcing needed depending on method used?

Mortar mix with a lot of clean brick, block or stone rubble is one
possibility. Block the inside as you go to keep it in place until it
sets and work from the outside to inside. Doesn't need anything fancy,
just chunks of whatever is compatible with the mortar. HTH

Joe