I am planning on building a game room onto my house, I have a 24' x 18' x 4" thick patio slab now (the outer end is a 12foot radius I plan to sqaure up) and plan on expanding it to 24' x 27', I plan to raise the level to be even with my house approx. 4" and pour 18 inch footings around the perimiter, what is the best way to achieve a good bond between the old and new and what is involved.