Melin Sguthan or Union Mill, Gaerwen is a rubblestone tower 9.1 metres high and 5.8 metres internal diameter, with two segmental headed doors opposite one another, and some segmental headed and other square windows. Holes in the internal walls held pairs of beams (fragments of which survive) supporting floors at 3.05, 6.05 and 8.1 metres above ground. Extra beams below the middle pairsupported the main shaft and great spur wheel, driving two pairs of stones on the second floor. An iron bearing journal in a wooden frame denotes the position of the horizontal shaft which drove the sack hoist, and recesses in the internal walls probably show the positions of grain cleaning and flour dressing machinery. The main frame and other parts of the base of the cap are still in position, as is most of the cast iron toothed ring which topped the stone tower. The cap would bave been turned by pulling on an endless chain round a wheel which turned a pinion meshing with this ring. The iron brake band which once encircled the brake wheel still hangs from the cap frame.
In 1974 fragments of french and Anglesey millstones were seen. In 2006 the interior was inaccessible due to the growth of vegetation.
In 2009 an application for Listed Building Consent for conversion and extension to form a dwelling was submitted to Ynys Mon Council.
W J Crompton, RCAHMW, 10 June 2010.

In 2012, it was noted that following Listed Building Consent, a conical 'Chinese hat' roof was in process of erection on top of the tower.
RCAHMW, 30 January 2012.