After Petra's retirement, Hartman started working with former Petra singer, John Schlitt, as II Guys from Petra in an album which was released in January 26, 2007 titled Vertical Expressions.
The reprise features an all-star chorus, including CCM industry "well-knowns": John Schlitt, Bob Hartman, LuLu Roman, members from the Winans family, Rick Cua, Kenny Marks, Lisa Bevill, Randy Thomas and Andy Denton.
Bob Dylan | Bob Hope | Bob Marley | Bob Hawke | Bob Geldof | Billy Bob Thornton | Bob Dole | Bob Seger | Bob the Builder | Bob Saget | Bob Hoskins | Bob Berg | Bob Knight | Bob Graham | Bob Brookmeyer | Bob Monkhouse | Bob Gibson | Bob Fosse | Bob Brady | Bob Feller | Bob Casey, Jr. | Bob Barker | The Bob Newhart Show | Bob Weir | Bob Harris | Bob Ezrin | Bob Balaban | Bob | Bob Woodward | Bob McDonnell |
Along with fellow newcomers to the band, Pete Orta and Kevin Brandow, he contributed (along with Petra's founder and songwriter, Bob Hartman) to the songwriting of Petra's album God Fixation in 1998.
Weaver is now touring with Classic Petra and has been re-united with his old friends from the original line-up of Petra: Bob Hartman, Greg X. Volz, John Lawry and Mark Kelly, having recorded Back to the Rock in 2010, his first studio album with the Classic Petra lineup since Beat the System in 1984.
Also released in March 2007 was a duet project by John Schlitt and Bob Hartman entitled Vertical Expressions, under the band name II Guys From Petra.
Most of the original songs were penned by band founder Bob Hartman (except "Song of Moses" that was written by former keyboardist Jim Cooper and well-known musician Brian Wooten).