Built on the site of Lagavulin distillery in the structure of the old Ardmore distillery. Closed in 1960 and got together with Lagavulin distillery in 1962.
From the site islayinfo.com/lostdistilleries:
When Sir Peter Mackie lost his bitter legal dispute to retain the sales agency for Laphroaig whisky in 1907 he reacted in characteristic style by deciding to make his own "Laphroaig" type whisky, and in 1908 built a tradition small pot-still distillery within the Lagavulin complex. Despite hiring staff from Laphroaig and attempting to copy the Laphroaig recipe, it did not succeed, perhaps because it used a different water source. Malt Mill tried to replicate a traditional style of Islay Whisky, using only peat-dried malt, and it is reputed to have had heather added to the mash. It was always a small scale operation producing 25,000 gallons of proof spirit (113,500 litres) in its first year, compared with 128,000 gallons (581,120 litres) at Lagavulin. What is perhaps surprising is that it survived until 1962 when it was merged with Lagavulin and its coal-fired stills moved to the latter's still house for another seven years use. The Malt Mill distillery building is now the reception centre within the Lagavulin Distillery site.