  We probe the radial clumping stratification of OB stars in the intermediate
and outer wind regions (r>~2 R*) to derive upper limits for mass-loss rates,
and compare to current mass-loss implementation. Together with archival
multi-wavelength data, our new far-infrared continuum observations for a sample
of 25 OB stars (including 13 B Supergiants) uniquely constrain the clumping
properties of the intermediate wind region. We derive the minimum radial
stratification of the clumping factor through the stellar wind, fclmin(r), and
the corresponding maximum mass-loss rate, Mdotmax, normalising clumping factors
to the outermost wind region (clfar=1). The clumping degree for r>~2 R*
decreases or stays constant with increasing radius for almost the whole sample.
There is a dependence on luminosity class and spectral type at the intermediate
region relative to the outer ones: O Supergiants (OSGs) present a factor 2
larger clumping factors than B Supergiants (BSGs). The maximum clumping of
roughly 1/3 of the OB Supergiants occurs close to the wind base (r<~2 R*) and
then decreases monotonically. This contrasts with the more frequent case where
the lowermost clumping increases towards a maximum, and needs to be addressed
by theoretical models. Additionally, the estimated Mdotmax for BSGs is at least
one order of magnitude lower than theoretical values, whereas for OSGs our
results and predictions agree within errors. Assuming values of clfar=4-9 from
hydrodynamical models would imply a reduction of mass-loss rates included in
stellar evolution models by a factor 2-3 for OSGs and by factors 6-200 for BSGs
below the first bi-stability jump. This implies large reductions of mass-loss
rates applied in evolution-models for BSGs, independently of the actual
clumping properties of these winds, and a thorough re-investigation of BSG
mass-loss rates and their effects on stellar evolution.
