If I do a solo at a gig, I never slap unless accompanied by the drums.
Otherwise, I dont know, just makes me feel a bit silly..Like Im trying too hard to show off.
What I usually do is explain to my drummer how its going to go; "Start with this mellow thing here...then move into this..gradually build it up...then you come in with the drum roll..and then i'll slap..then when I stop, you have your solo.."
I only slap if the line grooves, but I wouldn't solo slapstyle. Doing that just screams look at me, I would rather do a little improvised, melodic fingerstyle line.
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