Hi!
Renting a concrete grinder today to clean the old mastic and adhesives the previous owner used for old carpet I ripped up a few months back.  Seems the original pad is 9’x11′.  When the previous owners added the in-law suite, an adjacent pad 16.5’x11′ was added.

The newer pad is a bit higher than the original, so I am going to try to level it off a bit, then use a self-leveling liquid to fill the space between the pads.  What liquid do I use?  There seems to be a lot of products on the market.  Should I fill the gap with a filler first so to not waste the liquid?

We intend to put down outdoor carpet after.  Seems to be a lot of debate on if a pad could/should be used.  Is there an issue is I put a pad down first?  I would want the pad for comfort purposes, but not if compromising the pad or the finish carpet.

Thanks everyone