Filling expansion joints before self-leveling concrete? [duplicate]

Question

I am adding self-leveling concrete to my basement flooring. I have expansion joints which are currently filled with a joint compound. How would I fill in the expansion joints so that I can cover the flooring with the self-leveling concrete mix?

Answer 1

Those look like control joints between a single slab not expansion joints found between slabs. Expansion joints will go down the full depth of the slab and should never be covered. Control joints are only partial depth. Once the concrete fully cures most of the work of control joints is done whereas expansion joints need to continually expand and contract so they can't be covered with a rigid self leveling compound. If they are control joints, clean out any debris from the joints. Then you need to fill the joints with a flexible filler like “DAP Flexible floor patch and leveler“. That will ensure your joints continue to function as much as possible and not fill with leveling compound.