so, you're referring to
this layout from plesur
...and in this layout plesur used film caps for C8-9-10-11 (all 2,2 Uf); only C7 is polarized (electrolytic)
if you scroll down the thread page you can see some pics of his build also: some big WIMA 2,2 Uf film caps are used
so you don't see the polarity in the schematic because those are film (non-polarized!) capacitors!
...but if you search a little you can find at page1 of that thread the version 0.2 of the schematic (slightly different from version 0.3, and with polarized caps)
now, take C11: in this schematic you see that the + side is toward pin 3 of the IC
look at the layout now: can you see the trace connecting C11 to pin 3 of the IC? well, now you know where the + goes.
EDIT: if you look at the pics of the
original pedal (always at page 1) you could also verify plesur's reverse-engineering work: can you see C11? is the little red TANTALUM (polarized) cap (...so yes: in the original effect tantalum capacitors are used). can you see the "+" marking on the PCB? the trace on the PCB connects the + side of the cap with pin 3 of the IC, you see that? ...ok, now you're REALLY sure about C11 orientation.