  In this paper we present new ALMA observations towards the proto-planet
hosting transitional disc of Herbig Ae/Be star HD 100546. This includes
resolved 1.3 mm continuum, $^{13}$CO and the first detection of C$^{18}$O in
this disc, which displays azimuthal asymmetry in regions spatially coincident
with structures previously identified in HST images related to spiral arms. The
lower limit on the mass of the dust disc is calculated to be
9.6x10$^{-4}$M$_\odot$. A firm lower-limit on the total gas mass calculated
from optically thin, mid-plane tracing C$^{18}$O (2-1) emission is
0.018M$_\odot$ assuming ISM abundances. These mass estimates provide an
estimate of gas-to-dust ratio in the disc of 19, the ratio will increase if
C$^{18}$O is relatively under-abundant in the disc compared to CO and H2.
Through deprojection and azimuthal averaging of the image plane we detect 1.3
mm continuum emission out to 290+/-10 au,$^{13}$CO to 390+/-10 au and C$^{18}$O
to 300+/-10au. We measure a radially increasing millimetre spectral index
between wavelengths of 867$\mu$m and 1.3 mm, which shows that grain sizes
increase towards the star, with solid particles growing to cm scales in the
inner disc.
